KR20220083605A - Piezoelectric single crystal-matrix grains composites, manufacturing method thereof and use for piezoelectric and dielectric articles using the same - Google Patents

Abstract

The present invention relates to a piezoelectric single-crystal-polycrystalline ceramic composite, a method for manufacturing the same, and piezoelectric and dielectric application parts using the piezoelectric single-crystal-polycrystalline ceramic composite.
The piezoelectric single crystal-polycrystalline ceramic composite of the present invention is composited by optimizing the particle size distribution between the piezoelectric single crystal and the polycrystalline ceramic particles and the volume ratio of the piezoelectric single crystal, thereby reducing the manufacturing cost by realizing the excellent piezoelectric properties of the piezoelectric single crystal and mass production. Therefore, it is applicable to piezoelectric application parts and dielectric application parts including an ultrasonic transducer, a piezoelectric actuator, a piezoelectric sensor, a dielectric capacitor, an electric field radiation transducer, an electric field-vibration radiation transducer using a piezoelectric single crystal-polycrystalline ceramic composite, Piezoelectric properties and price competitiveness can be improved.

Description

Piezoelectric single-crystal-polycrystalline ceramic composite, manufacturing method thereof, and piezoelectric and dielectric application parts using the same

The present invention relates to a piezoelectric single crystal-polycrystalline ceramic composite, a method for manufacturing the same, and piezoelectric and dielectric application parts using the same, and more particularly, to a high piezoelectric charge constant (d ₃₃ ) and low dielectric loss (Dielectric Loss, tan d) is a composite of piezoelectric single crystal and polycrystalline ceramic particles having It relates to a piezoelectric single-crystal-polycrystalline ceramic composite that can be manufactured by improving (brittleness) characteristics and simplifying the production process to enable mass production, a manufacturing method thereof, and piezoelectric and dielectric application parts using the same.

The piezoelectric single crystals of the perovskite crystal structure ([A][B]O ₃ ) have significantly higher dielectric constant (K ₃ ^T ), piezoelectric charge constant (d ₃₃ ) and electromechanical coupling coefficient compared to conventional piezoelectric polycrystalline materials. (k ₃₃ ), it is used in high-performance parts such as piezoelectric actuators, ultrasonic transducers, piezoelectric sensors and dielectric capacitors, and its application is expected as a substrate material for various thin film devices.

The piezoelectric single crystals with perovskite crystal structure developed so far include PMN-PT (Pb(Mg _1/3 Nb _2/3 )O ₃ -PbTiO ₃ ), PZN-PT (Pb(Zn _1/3 Nb _{2/) 3} )O ₃ -PbTiO ₃ ), PInN-PT (Pb(In _1/2 Nb _1/2 )O ₃ -PbTiO ₃ ), PYbN-PT (Pb(Yb _1/2 Nb _1/2 )O ₃ -PbTiO ₃ ), PSN-PT (Pb(Sc _1/2 Nb _1/2 )O ₃ -PbTiO ₃ ), BiScO ₃ -PbTiO ₃ (BS-PT), PMN-PInN-PT and PMN-PYbN-PT, etc. . These single crystals undergo a congruent melting behavior during melting, and have been typically manufactured by conventional single crystal growth methods, such as the flux method, the Bridgman method, and the like.

However, the previously developed piezoelectric single crystals of PMN-PT and PZN-PT have the advantage of showing high dielectric and piezoelectric properties (K ₃ ^T >4,000, d ₃₃ >1,400 pC/N, k ₃₃ >0.85) at room temperature, Defects such as low phase transition _temperatures (TC and T _RT ), low coercive field ( _EC ), brittleness and high manufacturing cost significantly limit the utilization of piezoelectric single crystals.

In general, piezoelectric single crystals having a perovskite-type crystal structure are known to have the highest dielectric and piezoelectric properties in the region near the rhombohedral phase and tetragonal phase boundary, that is, near the morphotropic phase boundary (MPB) composition. It is known that a tetragonal piezoelectric single crystal can be used in some specific crystal directions with excellent piezoelectric or electro-optical properties.

However, since piezoelectric single crystals with a perovskite crystal structure generally show the best dielectric and piezoelectric properties when they are rhombohedral, the application of rhombohedral piezoelectric single crystals is most active, but rhombohedral piezoelectric single crystals are rhombohedral and tetrahedral. Since it is stable only below the phase transition temperature (T _RT ) _of Therefore, when the T _RT phase transition temperature is low, the operating temperature of the rhombohedral piezoelectric single crystal is lowered, and the manufacturing temperature and operating temperature of the piezoelectric single crystal application part are also limited to T _RT or less.

In addition, when the phase transition _temperatures (TC and T _RT ) and the coercive field (EC ) are low, the piezoelectric single crystals are easily _depolated under machining, stress, heat generation and driving voltage and exhibit excellent dielectric and piezoelectric properties. will lose Therefore, piezoelectric single crystals with low phase transition _temperatures (TC and T _RT ) and coercive field ( _EC ) are limited in single crystal application part manufacturing conditions, operating temperature conditions, and driving voltage conditions. For PMN-PT single crystals, T _C <150 °C, T _RT <80 °C and E _C <2.5 kV/cm are generally; for PZN-PT single crystals, T _C <170 °C, T _RT <100 °C and E _C <3.5 kV/cm. In addition, dielectric and piezoelectric application parts made of these piezoelectric single crystals have limited manufacturing conditions, operating temperature range, and operating voltage conditions, which has been an obstacle to the development and practical use of piezoelectric single crystal application parts.

In order to overcome the shortcomings of the piezoelectric single crystal, single crystals of new compositions such as PInN-PT, PSN-PT and BS-PT have been developed, and single crystal compositions mixed with each other such as PMN-PInN-PT and PMN-BS-PT have also been developed. is being studied

However, in the case of these single crystals, dielectric constant, piezoelectric charge constant, phase transition temperatures, coercive field and mechanical properties were not improved at the same time. Due to this, there is a problem that is an obstacle to the practical use of single crystals.

The reason why piezoelectric single crystals of perovskite-type crystal structure including PMN-PT developed so far show low phase transition temperature can be divided into three main reasons. First, relaxor, which is a main component together with PT; The point is that the phase transition temperature of PMN or PZN) is low.

In Non-Patent Document 1, the phase transition _temperatures (TC ) of the tetragonal and cubic phases of the perovskite-type structured piezoelectric ceramic polycrystals are presented in Table 1. Since the Curie temperature of the piezoelectric single crystal is similar to the Curie temperature of the polycrystal having the same composition, the Curie temperature of the piezoelectric single crystal can be estimated from the Curie temperature of the polycrystal.

Second, since the MPB, which forms the boundary between the tetrahedral phase and the rhombohedral phase, is not perpendicular to the temperature axis and is inclined gently, the Curie _temperature ( _TC ) Since the decrease is inevitable, it is difficult to simultaneously increase the Curie temperature (TC ) and the phase transition _temperature (T _RT ) of the rhombohedral and tetragonal phases.

Third, even when a relaxer (PYbN, PInN, BiScO ₃ , etc.) having a relatively high phase transition temperature is mixed with PMN-PT, etc., the phase transition temperature simply does not increase in proportion to the composition, or the dielectric and piezoelectric properties are lowered. Because.

Furthermore, the Relaxor-PT-based single crystals presented in Non-Patent Document 1 are mainly manufactured by the flux method and Bridgman method, which are conventional single crystal growth methods using a melting process. However, commercialization has not yet been successful due to the high cost and difficulty in mass production.

In addition, in general, piezoelectric ceramic single crystals have lower mechanical strength and fracture toughness than piezoelectric ceramic polycrystalline ceramics, so they are easily broken even by a small mechanical impact. The brittleness of the piezoelectric single crystal easily causes the destruction of the piezoelectric single crystal during the manufacture of application parts using the piezoelectric single crystal and the use of the applied parts, which has been a big limitation on the use of the piezoelectric single crystal. Therefore, in order to commercialize the piezoelectric single crystal, it is necessary to improve the dielectric and piezoelectric properties of the piezoelectric single crystal and simultaneously improve the mechanical properties of the piezoelectric single crystal.

On the other hand, Patent Document 1 is an invention related to a solid-state single crystal growth (SSCG) method, and unlike the conventional liquid-phase single crystal growth method, it does not use a melting process, and through a general heat treatment process without a special device. , by controlling the abnormal grain growth that occurs in polycrystals, allowing single crystals of various compositions to be manufactured by the solid-phase single crystal growth method, thereby lowering the cost of single crystal production, and single crystal growth capable of mass production of single crystals with high reproducibility and economical method presenting a way

In addition, Patent Document 2 discloses a high dielectric constant (K ₃ ^T ), a high piezoelectric constant (d ₃₃ and k ₃₃ ), a high phase transition temperature (Curie temperature, Tc) and a high coercive field using a solid-phase single crystal growth method. Disclosed is a piezoelectric single crystal having (coercive electric field, Ec) and improved mechanical properties at the same time. The piezoelectric single crystal manufactured through the solid-phase single crystal growth method suitable for mass production of single crystals is a piezoelectric single crystal by developing a single crystal composition that does not contain expensive raw materials. enable commercialization.

However, in general, compared to piezoelectric polycrystalline ceramics, piezoelectric single crystals show a higher piezoelectric charge constant, but are easily depolated due to a low coercive field, so electrical stability is low, so practical use is limited. Accordingly, a method of increasing the coercive field of the piezoelectric single crystal has been proposed, but the increase in the coercive field is a problem that is accompanied by a decrease in the piezoelectric properties, and still has low effectiveness.

Recently, research results and patents for dramatically increasing the piezoelectric charge constant by changing the composition of the piezoelectric polycrystalline ceramic (addition of Sm, etc.) have been published [Non-Patent Document 2].

In this case, it succeeded in raising the piezoelectric charge constant (d ₃₃ ) of the piezoelectric polycrystalline ceramic to 1,000 [pC/N] or more, but the phase transition temperature or Curie _temperature (TC ) is greatly reduced, and the dielectric loss (tan d) is greatly increased, which still greatly limits its application to general piezoelectric applications. Therefore, it is essential to develop a piezoelectric ceramic having a high piezoelectric charge constant and a high phase transition temperature and low dielectric loss (tan d) in order to be practically applied.

However, in general piezoelectric polycrystalline ceramics, matrix particles are arranged in disordered directions, and thus do not exhibit high piezoelectric properties like piezoelectric single crystals.

In order to solve this problem, a templated grain growth process in which the direction of particles is arranged in a characteristic direction in polycrystalline ceramics has been proposed, and in the existing templated grain growth process, a specific shape (e.g., ; thin plate-shaped) seed single crystals are arranged in a specific direction inside the polycrystal, and crystal oriented ceramics are manufactured through a heat treatment process of growing the seed single crystals in a specific direction. In this case, single seed crystals remain inside the grown crystal-oriented particles or disappear through reaction.

It was confirmed that the crystal-oriented ceramic manufactured through the crystal alignment growth process exhibits relatively high piezoelectric properties compared to general polycrystalline ceramics. However, the process cost of producing a seed single crystal of a specific shape suitable for the crystal orientation growth process is very high, and as a result, it is difficult to commercialize the crystal orientation ceramic due to the high manufacturing cost and difficulty in mass production.

Therefore, without using a seed single crystal of a specific shape and a seed single crystal arrangement process, the manufacturing process is simplified, so that the manufacturing cost is lowered and a process capable of mass production is required.

Accordingly, as a result of the present inventors' efforts to improve the conventional problems, the piezoelectric single crystal, which is limited to various applications due to the difficulty of mass production and the high manufacturing process price, in spite of excellent piezoelectric properties, is composited with polycrystalline ceramic particles, but the piezoelectric single crystal and the polycrystalline ceramic A piezoelectric single crystal that can be manufactured by simplifying the production process to enable mass production while maintaining high piezoelectric properties of the piezoelectric single crystal by optimizing the particle size distribution between particles and the volume ratio of the piezoelectric single crystal, and improving the mechanical properties of suppressing brittleness The present invention was completed by providing a polycrystalline ceramic composite and confirming the physical properties of the piezoelectric single-crystal-polycrystalline ceramic composite.

Korean Patent No. 0564092 (published on March 27, 2006) Korean Patent No. 0743614 (published on July 30, 2007)

IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, vol. 44, no. 5, 1997, pp. 1140-1147. Appl. Mater. Interfaces　2019, 11, 46, 43359-43367 High-Performance Sm-Doped Pb(Mg1/3Nb2/3)O3-PbZrO3-PbTiO3-Based Piezoceramics.

It is an object of the present invention to provide a piezoelectric single crystal-polycrystalline ceramic composite.

Another object of the present invention is to provide a method for manufacturing a piezoelectric single crystal-polycrystalline ceramic composite.

Another object of the present invention is to apply the piezoelectric single crystal-polycrystalline ceramic composite to piezoelectric application parts and dielectric application parts.

In order to achieve the above object, the present invention is a composite in which a piezoelectric single crystal of a perovskite structure ([A][B]O ₃ ) and polycrystalline ceramic particles are complexed, and the average particle size distribution of the piezoelectric single crystal ( a) is 100 to 1,000 μm, an average particle size distribution (b) of the polycrystalline particles is 2 to 20 μm, and a piezoelectric single crystal-polycrystalline ceramic composite having a particle size distribution a/b of 20 to 100 is provided.

In the piezoelectric single crystal-polycrystalline ceramic composite, it is preferable that the piezoelectric single crystal is contained in an amount of 30 to 80 vol%, and the piezoelectric single crystals are oriented in a specific crystal direction in the composite. Preferably, the specific crystal direction of the piezoelectric single crystal is a <001> or <011> direction.

The piezoelectric single-crystal-polycrystalline ceramic composite composited by optimizing the particle size distribution between the piezoelectric single crystal and the polycrystalline ceramic particles and the volume ratio of the piezoelectric single crystal is obtained at room temperature (1) dielectric constant (K ₃ ^T ) is 3,000 or more, (2) The piezoelectric charge constant (d ₃₃ ) is 1,200 pC/N or more and (3) the first phase transition temperature is 80° C. or more, maintaining the high piezoelectric properties of the piezoelectric single crystal and brittleness ) to improve the mechanical properties of the inhibition.

In the piezoelectric single crystal-polycrystalline ceramic composite of the present invention, there is a phase transition between ferrofluid phases (rhombohedral phase and tetragonal phase, etc.) below the Curie _temperature (TC ), and the dielectric constant (K ₃ ^T of the piezoelectric single crystal-polycrystalline ceramic composite) ) has the characteristic that the phase transition temperature between the ferrofluid phases is three times higher than the room temperature.

In addition, the ratio [d ₃₃ /tand] of the piezoelectric charge constant (d ₃₃ , pC/N) to the dielectric loss (tand (%)) at room temperature is 1,000 or more, and the piezoelectric charge constant ( d ₃₃ , pC/N), piezoelectric voltage constant (g ₃₃ , 10 ^-3 Vm/N)) and dielectric loss (tand%) ratio [(d ₃₃ ⅹg ₃₃ )/tand] is 25,000 or more to implement

In the piezoelectric single crystal-polycrystalline ceramic composite of the present invention, the piezoelectric single crystal is a piezoelectric single crystal having a perovskite-type structure ([A][B]O ₃ ), preferably a piezoelectric single crystal having the composition formula of the following Chemical Formula 1.

Formula 1

[A _1-(a+1.5b) B _a C _b ][(MN) _1-xy (L) _y Ti _x ]O _3-z

wherein A is Pb or Ba,

B is at least one selected from the group consisting of Ba, Ca, Co, Fe, Ni, Sn and Sr, and C is Co, Fe, Bi, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, At least one selected from the group consisting of Tb, Dy, Ho, Er, Tm, Yb and Lu, L is a single or mixed form selected from Zr or Hf, M is Ce, Co, Fe, In, Mg, Mn, Ni, Sc, Yb, and at least one selected from the group consisting of Zn, N is at least one selected from the group consisting of Nb, Sb, Ta and W, 0<a≤0.10, 0<b≤0.05, 0.05≤x≤0.58 and 0.05≤y≤0.62 and 0≤z≤0.02.

In the piezoelectric single crystal having the composition formula of Formula 1, it is preferable that the porosity in the single crystal is 0.5 vol% or more.

In the piezoelectric single crystal having the composition formula of Formula 1 of the present invention, the composition satisfies 0.01≤a≤0.10 and 0.01≤b≤0.05, and more preferably satisfies a/b≥2 in the above formula.

In the piezoelectric single crystal having the composition formula of Formula 1 of the present invention, it is more preferable that 0.10≤x≤0.58 and 0.10≤y≤0.62 are satisfied.

When L is a mixed form in the piezoelectric single crystal, it has a compositional formula of the following Chemical Formula 2 or Chemical Formula 3.

Formula 2

[A _1-(a+1.5b) B _a C _b ][(MN) _1-xy (Zr _1-w , Hf _w ) _y Ti _x ]O ₃

Formula 3

[A _1-(a+1.5b) B _a C _b ][(MN) _1-xy (Zr _1-w , Hf _w ) _y Ti _x ]O _3-z

In the above, A, B, C, M, N, a, b, x, y and z are the same as in Formula 1 or 2, but represent 0.01≤w≤0.20.

At this time, the piezoelectric single crystal has a Curie temperature (Tc) of 180 °C or higher, and at the same time a phase transition temperature between rhombohedral phase and tetragonal phase (T _RT ) is 100 °C or higher. A coupling coefficient (longitudinal electromechanical coupling coefficient, k ₃₃ ) is 0.85 or more, and a coercive electric field (Ec) satisfies 4 to 12 kV/cm.

In particular, the piezoelectric single crystal satisfies a dielectric constant (K ₃ ^T ) of 4,000 or more, preferably 4,000 to 15,000, and a piezoelectric charge constant (d ₃₃ ) of 1,400 or more, preferably 1,400 to 6,000 pC/N.

The present invention provides a method for producing the piezoelectric single-crystal-polycrystalline ceramic composite,

Prepare single crystal particles (a) by pulverizing a piezoelectric single crystal of a perovskite structure ([A][B]O ₃ ) to 50 μm or more,

Prepare polycrystalline powder particles (b) with an average particle size distribution of 0.1 to 5 μm, mix with a particle size distribution a/b of 20 or more, and heat-treat,

Growing the piezoelectric single crystal to a particle size of 100 μm or more by the heat treatment,

Provided is a method for manufacturing a piezoelectric single-crystal-polycrystal ceramic composite in which a particle size distribution a/b after heat treatment becomes 20 to 100.

Before the heat treatment, in the mixing step, the piezoelectric single crystal contains 80% by volume or less, and the piezoelectric single crystal after the heat treatment contains the single crystal in the range of 30 to 80% by volume.

In addition, the average particle size distribution (a) of the piezoelectric single crystal grown after the heat treatment is 100 μm or more, more preferably 100 to 1,000 μm, and the average particle size distribution (b) of the grown polycrystalline particles is 2 to 20 μm, , a piezoelectric single-crystal-polycrystalline ceramic composite satisfying the requirement of the particle size distribution a/b of 20 to 100 was prepared.

At this time, the heat treatment is performed at 900 to 1,300° C. for 1 to 100 hours, and is preferably performed at a temperature increase rate of 1 to 20° C./min.

Furthermore, the present invention provides a piezoelectric application component and a dielectric application component including the piezoelectric single crystal-polycrystalline ceramic composite.

Specifically, piezoelectric single-crystal-polycrystalline ceramic composites including ultrasonic transducers, piezoelectric actuators, piezoelectric sensors, dielectric capacitors, and electric field generating transducers (Electric Field Generating Transducers) ) and an electric field-can be applied to any one selected from the group consisting of vibration radiation transducers (Electric Field and Vibration Generating Transducers).

The piezoelectric single-crystal-polycrystalline ceramic composite according to the present invention is The dielectric properties of a piezoelectric single crystal having a dielectric constant (K ₃ ^T ≥ 4,000) and a piezoelectric charge constant (d ₃₃ ≥ 1,400 pC/N) are preserved without being suppressed inside the composite, so that the dielectric and The piezoelectric charge constant (d ₃₃ ≥ 1,200 pC/N) is also highly conserved, and mass production is possible with low process costs.

Since the piezoelectric single-crystal-polycrystalline ceramic composite of the present invention can be mass-produced at a low price with excellent piezoelectric properties, it is possible to satisfy the performance and price competitiveness of piezoelectric application parts and dielectric application parts using the same.

1 is a piezoelectric single crystal of Example 1 of the present invention - [Pb _0.965 Sr _0.02 La _0.01 ] [(Mg _1/3 Nb _2/3 ) _0.4 Zr _0.25 Ti _0.35 ]O ₃ piezoelectric single crystal contained in the polycrystalline ceramic composite,
2 is a piezoelectric single-crystal-polycrystalline ceramic composite prepared according to the change in size and volume fraction in Example 1 of the present invention;
3 is [Pb _0.965 Sr _0.02 Sm _0.01 ][(Mg _1/3 Nb _2/3 ) _0.25 (Ni _1/3 Nb _2/3 ) _0.10 included in the piezoelectric single crystal-polycrystalline ceramic composite of Example 2 of the present invention; FIG. Zr _0.30 Ti _0.35 ]O ₃ piezoelectric single crystal,
4 is a piezoelectric single-crystal-polycrystalline ceramic composite prepared according to the change in size and volume fraction in Example 2 of the present invention;
5 is a result of a change in dielectric properties and a phase transition phenomenon according to temperature of a PMN-PT piezoelectric single crystal manufactured by a solid-phase single crystal growth method;
6 is a result of the change in dielectric properties and the phase transition phenomenon according to the temperature of the [Pb _0.965 Sr _0.02 La _0.01 ][(Mg _1/3 Nb _2/3 ) _0.4 Zr _0.25 Ti _0.35 ]O ₃ piezoelectric single crystal prepared by the solid-phase single crystal growth method. ,
7 is a result of observing the change in dielectric properties and the phase transition according to the temperature of the piezoelectric single-crystal-polycrystalline ceramic composite prepared in Example 1 of the present invention.

Hereinafter, the present invention will be described in detail.

The present invention is a composite in which piezoelectric single crystal and polycrystalline ceramic particles of a perovskite structure ([A][B]O ₃ ) are complexed, (1) the difference between the particle sizes of the piezoelectric single crystal and the polycrystalline ceramic is specified in an optimal ratio. In this case, the excellent piezoelectric properties of the piezoelectric single crystal are preserved, and (2) the piezoelectric and mechanical properties of the composite can be improved by optimizing the difference in composition between the piezoelectric single crystal and the polycrystalline ceramic particles.

More specifically, in the piezoelectric single crystal-polycrystalline ceramic composite of the present invention, the average particle size distribution (a) of the piezoelectric single crystal is 100 to 1,000 μm, and the average particle size distribution (b) of the polycrystalline particles is 2 to 20 μm, The particle size distribution a/b is 20 to 100.

In addition, the volume ratio of the piezoelectric single crystal and the polycrystalline ceramic particle is optimized so that the piezoelectric single crystal is contained in an amount of 30 to 80 vol% in the piezoelectric single crystal-polycrystalline ceramic composite of the present invention.

In general, in the case of a composite in which a piezoelectric single crystal having a high piezoelectric charge constant (d ₃₃ ≥1,400 pC/N) is complexed with polycrystalline ceramic particles, the piezoelectric charge constant (d ₃₃ ≤1,000 pC/N) tends to be significantly lower. However, this level of complex has low practical application value.

On the other hand, the present invention provides high piezoelectric properties (piezoelectric charge constant, d ₃₃ ≥ 1,200 pC/N) of the piezoelectric single crystal by optimizing (1) the particle size distribution between the piezoelectric single crystal and the polycrystalline ceramic particles and (2) the content volume ratio of the piezoelectric single crystal. ), it is possible to provide a piezoelectric single-crystal-polycrystalline ceramic composite that can be manufactured by simplifying the production process to enable mass production while improving the mechanical properties of suppressing brittleness.

The piezoelectric single crystal is not particularly limited in shape, but isotropic shapes such as a sphere and a cube are preferable in order to increase the overall density of the composite by increasing the packing density in the matrix phase.

In addition, the piezoelectric single crystals in the composite may be arranged in a disordered direction, but preferably, when the piezoelectric single crystals are oriented in a specific crystal direction, the piezoelectric properties may be further improved. In this case, the specific crystal direction of the piezoelectric single crystal is the <001> or <011> direction.

Since the piezoelectric single crystal of the present invention does not grow a piezoelectric single crystal by using a specific seed single crystal inside the matrix, unlike the existing Templated Grain Growth process, the piezoelectric single crystal of the present invention is used for single crystal growth. It does not contain a seed single crystal or a seed single crystal that is destroyed after single crystal growth.

Therefore, since the process cost for producing a specific seed single crystal is omitted, the manufacturing process is simplified, the manufacturing cost is lowered, and mass production is possible.

However, although some piezoelectric single crystals are grown during the process of mixing the externally grown piezoelectric single crystal and polycrystalline ceramic powder and sintering the composite, it is not an essential process as in the existing Templated Grain Growth process.

The piezoelectric single crystal-polycrystalline ceramic composite in which (1) the particle size distribution between the piezoelectric single crystal and the polycrystalline ceramic particles and (2) the content volume ratio of the piezoelectric single crystal is optimized

① At room temperature, the dielectric constant (K ₃ ^T ) is 3,000 or more,

② At room temperature, the piezoelectric charge constant (d ₃₃ ) is 1,200 pC/N or more and

③ The phase transition temperature that appears first at room temperature realizes the characteristic of 80℃ or higher.

In the above, the term "room temperature" means that the physical property evaluation is performed under the same temperature condition in the room temperature range, and unless otherwise specified in the specification of the present invention, the room temperature is performed at a temperature of 30°C.

More specifically, the piezoelectric single crystal-polycrystalline ceramic composite of the present invention exhibits a phase transition phenomenon between ferrofluid phases (rhombohedral phase and tetragonal phase, etc.) below the Curie _temperature (TC ). Preferably, the dielectric constant (K ₃ ^T ) of the piezoelectric single crystal is higher than the Curie temperature (T _C ) at the phase transition temperature between the ferrofluid phases.

More preferably, the dielectric constant (K ₃ ^T ) of the piezoelectric single-crystal-polycrystalline ceramic composite is three times higher at the phase transition temperature between ferrofluid phases than at room temperature.

In addition, in general, the piezoelectric single crystal has a high piezoelectric charge constant (d ₃₃ ) and a low dielectric loss (tan d). On the other hand, in the case of a piezoelectric polycrystalline ceramic, the piezoelectric charge constant (d ₃₃ ) and the dielectric loss (tan d) simultaneously increase, so that the polycrystalline piezoelectric ceramic having a high piezoelectric charge constant and a low dielectric loss (tan d) at the same time is difficult to develop.

Accordingly, in the present invention, the piezoelectric single crystal having a high piezoelectric charge constant (d ₃₃ ) and a low dielectric loss (tan d) is maximized, and the piezoelectric charge constant (d ₃₃ ) of the composite is maximized and the dielectric loss (tan d) is As a result, the ratio of piezoelectric charge constant (d ₃₃ , pC/N) and dielectric loss (Dielectric Loss, tand (%)) [= d ₃₃ /tand] is maximized to 1,000 or more.

In addition, the piezoelectric single crystal-polycrystalline ceramic composite of the present invention has a small increase in the dielectric constant, so the piezoelectric charge constant (d ₃₃ , pC/N), the piezoelectric voltage constant (g ₃₃ , 10 ^-3 Vm/N) at room temperature ) and dielectric loss (tand%) ratio [(d ₃₃ ⅹg ₃₃ )/tand] is maximized to 25,000 or more at the same time.

In addition, in the piezoelectric single-crystal-polycrystalline ceramic composite of the present invention, a part or all of the empty space inside the composite may be filled with a polymer. In this case, a flexible matrix material such as a polymer and an epoxy inside the composite enables low-temperature molding of the composite and imparts flexibility.

The piezoelectric single crystal used in the piezoelectric single crystal-polycrystalline ceramic composite of the present invention has a high dielectric constant (K ₃ ^T ≥ 4,000), a piezoelectric charge constant (d ₃₃ ≥ 1,400 _pC /N), and a coercive field (EC ≥ 4 to 12 kV/ cm).

More specifically, the piezoelectric single crystal used in the present invention is a piezoelectric single crystal having a perovskite structure ([A][B]O ₃ ), and is preferably a piezoelectric single crystal having the composition formula of the following Chemical Formula 1.

Formula 1

[A _1-(a+1.5b) B _a C _b ][(MN) _1-xy (L) _y Ti _x ]O _3-z

wherein A is Pb or Ba,

B is at least one selected from the group consisting of Ba, Ca, Co, Fe, Ni, Sn and Sr,

C is at least one selected from the group consisting of Co, Fe, Bi, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu,

L is a single or mixed form selected from Zr or Hf,

M is at least one selected from the group consisting of Ce, Co, Fe, In, Mg, Mn, Ni, Sc, Yb and Zn,

N is at least one selected from the group consisting of Nb, Sb, Ta and W,

0<a≤0.10, 0<b≤0.05, 0.05≤x≤0.58 and 0.05≤y≤0.62 and 0≤z≤0.02.

In the piezoelectric single crystal having the composition formula of Chemical Formula 1, it is preferable that the porosity in the single crystal is 0.5% by volume or more.

The piezoelectric single crystal having the composition formula of Formula 1 of the present invention is based on the tendency of the piezoelectric properties to further increase as the chemical composition is compounded, and in the perovskite crystal structure ([A][B]O ₃ ), [A] The site ions are made up of complex compositions.

At this time, if the complex composition of the [A] site ion in the piezoelectric single crystal having the composition formula of Formula 1 is specifically examined, it may be composed of [A _1-(a+1.5b) B _a C _b ], and the A composition is flexible or In the embodiment of the present invention containing lead-free element and A is Pb, but will be described limited to the flexible-based piezoelectric single crystal, but will not be limited thereto.

In the site ion [A], the B composition is a metal divalent element, preferably at least one selected from the group consisting of Ba, Ca, Co, Fe, Ni, Sn and Sr, and the C composition is a metal trivalent element. If it is an element, use it.

Preferably, it is at least one selected from the group consisting of Co, Fe, Bi, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, more preferably Preferably, the lanthanide element is used as one type or a mixture of two types.

In the embodiments of the present invention, in the [A] site ion, the C composition is described as a single or a mixed composition including Sm, but the present invention will not be limited thereto.

In the complex composition of the site ion [A] in the piezoelectric single crystal having the composition formula of Formula 1 above, the [A _1-(a+1.5b) B _a C _b ] composition corresponding to the site ion [A] has the desired physical properties. As a requirement for implementation, when A is a lead-based or lead-free piezoelectric single crystal, it is characterized in that it is composed of a combination of a metal divalent element and a metal trivalent element.

That is, 0.01≤a≤0.10 and 0.01≤b≤0.05 must be satisfied, and more preferably a/b≥2 is satisfied. At this time, if a is less than 0.01 in the above, there is a problem that the perovskite phase is unstable, and if it exceeds 0.10, the phase transition temperature is too low, which makes practical use difficult, which is not preferable.

In addition, if the a/b≥2 requirement is not satisfied, it is undesirable because dielectric and piezoelectric properties are not maximized or single crystal growth is limited.

In this case, in the composite composition of the [A] site ion in the piezoelectric single crystal having the composition formula of Formula 1, it is possible to implement an excellent dielectric constant in the case of the composite composition compared to the case where the metal trivalent element or the metal divalent element is alone.

According to the generally known [A][MN]O ₃ -PbTiO ₃ -PbZrO ₃ phase diagram, it shows a compositional region exhibiting excellent dielectric and piezoelectric properties around the rhombohedral phase and the tetragonal phase boundary (MPB). In the [A][MN]O ₃ -PbTiO ₃ -PbZrO ₃ phase diagram, dielectric and piezoelectric properties are maximized at the rhombohedral and tetragonal phase boundary compositions, and the dielectric and piezoelectric properties gradually decrease as the composition moves away from the MPB composition. And in the case of within 5 mol% of the composition in the rhombohedral region in the MPB composition, the dielectric and piezoelectric properties were small, and very high dielectric and piezoelectric properties were maintained. In this case, the dielectric and piezoelectric properties decreased continuously, but showed high enough dielectric and piezoelectric properties to be applied to dielectric and piezoelectric applications. When the composition is changed from the MPB composition to the tetragonal region, the dielectric and piezoelectric properties decrease more rapidly than in the rhombohedral region. However, in the tetragonal region, dielectric and piezoelectric properties continuously decreased even within 5 mol% or within 10 mol% of the composition, but high enough dielectric and piezoelectric properties to be applied to dielectric and piezoelectric applications.

The phase boundary (MPB) of PbTiO ₃ and PbZrO ₃ is known as PbTiO ₃ : PbZrO ₃ = x: y = 0.48: 0.52 (molar ratio).

When the composition changes by 5 mol% in the MPB composition to the rhombohedral and tetragonal regions, respectively, the maximum values of x and y are 0.53 and 0.57, respectively (that is, when x is the maximum, x: y = 0.53: 0.47, x: y = 0.43: 0.57) when y is the maximum. And when the composition changes by 10 mol% from the MPB composition to the rhombohedral and tetragonal regions, respectively, the maximum values of x and y are 0.58 and 0.62, respectively (that is, when x is the maximum, x: y = 0.58: 0.42, and , x: y = 0.38: 0.62) when y is the maximum. In the MPB composition, high dielectric and piezoelectric properties are maintained within the range of 5 mol% composition in the rhombohedral and tetragonal regions, respectively, and within the range of 10 mol% in the rhombohedral and tetragonal regions in the MPB composition, respectively. It exhibits sufficiently high dielectric and piezoelectric properties for applications in dielectric and piezoelectric applications.

In addition, when the contents of PbTiO ₃ and PbZrO ₃ , ie, x and y values, are less than 0.05, the phase boundary between the rhombohedral phase and the tetragonal phase cannot be formed, or the phase transition temperatures and the coercive field are too low, which is not suitable for the present invention.

In Formula 1, x preferably falls within the range of 0.05≤x≤0.58, and more preferably 0.10≤x≤0.58. At this time, when x is less than 0.05, the phase transition temperatures (Tc and T _RT ), piezoelectric charge constants (d ₃₃ , k ₃₃ ) or coercive field (Ec) are low, and when x exceeds 0.58, the dielectric constant (K ₃ ^T ) ), the piezoelectric charge constants (d ₃₃ , k ₃₃ ) or the phase transition temperature (T _RT ) are low. On the other hand, y preferably falls within the range of 0.050 ≤ y ≤ 0.62, and more preferably satisfies 0.10 ≤ y ≤ 0.62. The reason is that the phase transition temperatures (Tc and T _RT ), piezoelectric charge constants (d ₃₃ , k ₃₃ ) or coercive field (Ec) are low when y is less than 0.05 and the dielectric constant (K ₃ ^T ) when y is greater than 0.62. Alternatively, it is because the piezoelectric charge constants (d ₃₃ , k ₃₃ ) are low.

The piezoelectric single crystal having the composition formula of Formula 1 of the present invention includes a metal tetravalent element in the [B] site ion in the perovskite crystal structure ([A][B]O ₃ ), in particular for the L composition, It is limited to a single or mixed form selected from Zr or Hf.

In the case of the mixed form, a piezoelectric single crystal having a composition formula of the following Chemical Formula 2 or Chemical Formula 3 is provided.

Formula 2

[A _1-(a+1.5b) B _a C _b ][(MN) _1-xy (Zr _1-w , Hf _w ) _y Ti _x ]O ₃

Formula 3

[A _1-(a+1.5b) B _a C _b ][(MN) _1-xy (Zr _1-w , Hf _w ) _y Ti _x ]O _3-z

In the above, A, B, C, M, N, a, b, x, y and z are the same as in Formula 1 above, but represent 0.01≤w≤0.20.

At this time, when w is less than 0.01, there is a problem that the dielectric and piezoelectric properties are not maximized, and when it exceeds 0.20, it is not preferable because the dielectric and piezoelectric properties are rapidly reduced.

The piezoelectric single crystal having the composition formulas of Chemical Formulas 1 to 3 above has a perovskite-type crystal structure ([A][B]O ₃ ) By combining the complex composition of the [A] site ion and the composition of the [B] site ion, It is a piezoelectric single crystal with a Curie temperature (Tc) of 180 °C or higher and a phase transition temperature between rhombohedral phase and tetragonal phase (T _RT ) of 100 °C or higher at the same time. At this time, if the Curie temperature is less than 180 ℃, there is a problem that it is difficult to raise the coercive field (Ec) to 5 kV/cm or more or the phase transition temperature (T _RT ) to 100 °C or more.

In addition, in the piezoelectric single crystal having the composition formula of Formula 1 of the present invention, in the perovskite crystal structure ([A][B]O ₃ ), 0≤z≤ with respect to the oxygen vacancy at the [O] site. It is characterized in that it is controlled to 0.02. At this time, when the z exceeds 0.02, there is a problem in that dielectric and piezoelectric properties are rapidly lowered, which is not preferable.

When oxygen vacancy is induced in the above range, the coercive electric field and the internal electric field are effectively increased to increase the stability of the piezoelectric single crystal during electric field driving and under mechanical load conditions. Therefore, it is possible to maximize the piezoelectric properties and at the same time increase the stability.

The piezoelectric single crystal having the composition formula of Formula 1 according to the present invention has an electromechanical coupling coefficient (k ₃₃ ) of 0.85 or more, and if the electromechanical coupling coefficient is less than 0.85, the properties are similar to those of the piezoelectric polycrystalline ceramics, and the energy conversion efficiency is low. Not desirable.

The piezoelectric single crystal according to the present invention preferably has a coercive field ( _EC ) of 4 to 12 kV/cm, and if the coercive field is less than 4 kV/cm, easily polling when processing a piezoelectric single crystal or when manufacturing or using a piezoelectric single crystal application part There is a problem that (poling) is eliminated.

In addition, the piezoelectric single crystal according to the present invention simultaneously satisfies a high dielectric constant (K ₃ ^T ≥4,000 to 15,000) and a high piezoelectric charge constant (d ₃₃ ≥1,400 to 6,000 pC/N).

In addition, the piezoelectric single crystal having the composition formula of Chemical Formula 1 of the present invention may provide a uniform single crystal by having a composition gradient within the single crystal of 0.2 to 0.5 mol%.

The piezoelectric single crystal composition may further include a reinforced secondary phase (P) in an amount of 0.1 to 20% by volume, and the reinforced secondary phase P is a metal phase, an oxide phase, or a pore.

More specifically, the reinforced secondary phase P is at least one selected from the group consisting of Au, Ag, Ir, Pt, Pd, Rh, MgO, ZrO ₂ and pores, and the reinforced secondary phase P is a piezoelectric single crystal It is uniformly distributed in the form of particles in the interior or is regularly distributed with a certain pattern.

Further, in the piezoelectric single crystal, x and y are 10 mol% from the composition of the phase boundary (MPB) between the rhombohedral phase and the tetragonal phase, and more preferably, the x and y are from the phase boundary (MPB) composition of the rhombohedral phase and the tetragonal phase. It falls within the range of 5 mol%.

Lead zirconate (PbZrO ₃ ) not only has a high phase transition temperature of 230°C, but also has the effect of making the MPB more perpendicular to the temperature axis, maintaining a high Curie temperature while maintaining high rhombohedral and tetragonal phase transition temperatures (T _RT ), allowing development of compositions with high Tc and T _RT at the same time.

This is because, even when lead zirconate is mixed with the conventional piezoelectric single crystal composition, the phase transition temperature increases in proportion to the content of lead zirconate. Therefore, the piezoelectric single crystal of the perovskite type crystal structure containing zirconium (Zr) or lead zirconate can overcome the problems of the conventional piezoelectric single crystals.

In addition, zirconia (ZrO ₂ ) or lead zirconate is used as a main component in a conventional piezoelectric polycrystalline material, and since it is an inexpensive raw material, the object of the present invention can be achieved without increasing the raw material price of a single crystal.

On the other hand, the perovskite-type piezoelectric single crystal containing lead zirconate does not show a congruent melting behavior and exhibits an incongruent melting behavior, unlike PMN-PT and PZN-PT, when melting. Therefore, when the non-eutectic behavior is shown, the liquid phase and the solid phase ZrO ₂ are separated when the solid phase is melted, and the solid zirconia particles in the liquid phase interfere with the single crystal growth, so that the flux method and the Bridgman method, which are general single crystal growth methods that use the melting process, etc. cannot be manufactured with

In addition, it is difficult to manufacture a single crystal including a reinforced secondary phase by a general single crystal growth method using a melting process, and has not been reported yet. This is because, above the melting temperature, the reinforced secondary phase is chemically unstable and reacts with the liquid phase, so it cannot maintain an independent secondary phase form and disappear. In addition, due to the difference in density between the secondary phase and the liquid phase in the liquid phase, the secondary phase and the liquid phase are separated, making it difficult to manufacture a single crystal including the secondary phase, and furthermore, the volume fraction, size, and volume fraction of the reinforced secondary phase inside the single crystal The shape, arrangement, and distribution cannot be adjusted.

Accordingly, the present invention manufactures piezoelectric single crystals including a reinforced secondary phase by using a solid-phase single crystal growth method that does not use a melting process. In the solid-state single crystal growth method, since single crystal growth occurs below the melting temperature, the chemical reaction between the reinforced secondary phase and the single crystal is suppressed, and the reinforced secondary phase can stably exist in an independent form inside the single crystal.

In addition, single crystal growth occurs in a polycrystal including a reinforced secondary phase, and there is no change in volume fraction, size, shape, arrangement and distribution of the reinforced secondary phase during single crystal growth. Therefore, in the process of making a polycrystal including a reinforced secondary phase, if the volume fraction, size, shape, arrangement and distribution of the reinforced secondary phase inside the polycrystal are adjusted and the single crystal is grown, as a result, a single crystal including a reinforced secondary phase of a desired shape That is, second phase-reinforced single crystals can be manufactured.

Therefore, in the perovskite crystal structure ([A][B]O ₃ ), a piezoelectric single crystal cannot be manufactured with a composite composition by the flux method and the Bridgman method, which are conventional single crystal growth methods. In particular, in the case of the flux method including the melting process and the Bridgman method, the composition gradient inside the single crystal is produced in an amount of 1 to 5 mol% or more in the manufacturing process, whereas in the solid-phase single crystal growth method of the present invention, the composition gradient inside the single crystal is It can be prepared in a uniform composition of 0.2 to 0.5 mol%.

Therefore, in the present invention, in a perovskite-type crystal structure containing lead zirconate ([A][B]O ₃ ) by a solid-phase single crystal growth method, the complex composition of [A] site ions and [B] site ions By allowing the piezoelectric single crystal to grow uniformly even with a complex composition, the dielectric constant (K ₃ ^T ≥4,000 or more, preferably 4,000 to 15,000) and the piezoelectric charge constant (d ₃₃ ≥ 1,400 or more, preferably compared to conventional piezoelectric single crystals) For example, it is possible to provide a novel piezoelectric single crystal having significantly increased 1,400 to 6,000 pC/N) and high coercive field ( _EC ≥4 to 12 kV/cm).

In addition, the present invention prepares single crystal particles (a) by grinding a piezoelectric single crystal of a perovskite type structure ([A][B]O ₃ ) to 50 μm or more,

Prepare polycrystalline powder particles (b) with an average particle size distribution of 0.1 to 5 μm, mix with a particle size distribution a/b of 20 or more, and heat-treat,

It provides a method for producing a piezoelectric single crystal-polycrystalline ceramic composite in which the grain size of the piezoelectric single crystal is grown to 100 μm or more by the heat treatment, and the grain size distribution a/b after the heat treatment is 20 to 100.

The method for producing a piezoelectric single crystal of the present invention is performed according to a solid-phase single crystal growth method [see Patent Documents 1 and 2], and mass production is possible at a lower process cost compared to the flux method and the Bridgman method.

In addition, through the sintering process, the grain size is increased to a size of several tens to several hundred μm or more by maximizing grain growth in the polycrystalline ceramic (especially when using Abnormal Grain Growth), and the sintered By crushing the polycrystal, it is possible to obtain a piezoelectric single crystal or a piezoelectric single crystal aggregate having a size of several tens to several hundred μm.

When the piezoelectric single crystal is manufactured and selected in this way, the manufacturing cost of the piezoelectric single crystal can be lowered, so that the mass production of the composite is possible at a lower process price.

In the method for manufacturing a piezoelectric single crystal-polycrystalline ceramic composite according to the present invention, the excellent properties of the composite are due to the piezoelectric single crystal, but polycrystalline ceramic particles also occupy 20 to 70% by volume, so the selection of polycrystalline ceramic particles will be important.

In this case, the composition of the polycrystalline ceramic particles compounded with the piezoelectric single crystal represented by Formula 1 is the same as the composition represented by Formula 1, but may be distinguished from the piezoelectric single crystal according to a difference in each composition formula. In addition, when the compositions of the piezoelectric single crystal and the polycrystalline ceramic particles are different, a synergistic effect can be expected according to the combination of the two compositions.

The above polycrystalline ceramic is not limited thereto, and may include a known polycrystalline composition.

In this case, polycrystalline ceramic particles are required to have (1) high piezoelectric properties, (2) excellent sintering properties due to an increase in density during heat treatment, and (3) high mechanical properties of fracture toughness.

In the method for producing a piezoelectric single crystal-polycrystalline ceramic composite of the present invention, during the heat treatment process, the size of the polycrystalline ceramic particles as well as the piezoelectric single crystal of the perovskite structure ([A][B]O ₃ ) increases at the same time, so the heat treatment The grain size of the single-crystal for all tacks is preferably 50 µm or more. At this time, if the particle size of the single tack single crystal is less than 50 μm, the effect due to the complexing is insignificant because it is pulverized too small.

In addition, in the case of polycrystalline ceramic particles, the smaller the initial particle size, the more advantageous for densification.

In general, compared to before heat treatment, the particle size distribution ratio (a/b) decreases after heat treatment, so the particle size distribution ratio (a/b) before heat treatment should be mixed to 20 or more after heat treatment (a/b) b) may meet the requirements of 20 to 100.

Heat treatment so that the grain size of the piezoelectric single crystal grains grown during the heat treatment is 100 μm or more, and the particle size distribution ratio (a/b) between the piezoelectric single crystal grains (a) and the polycrystalline powder grains (b) after the heat treatment is 20 to 100 will be.

In addition, the single crystal grain growth during the heat treatment consumes the polycrystalline ceramic particles, that is, as the single crystal grows while the polycrystalline ceramic particles are included in the single crystal grains, the single crystal volume ratio also increases according to the growth of the single crystal grains during the heat treatment.

Therefore, it is preferable to optimize the initial input ratio of the piezoelectric single crystal before the heat treatment to be set to 80 vol% or less, and to be 30 to 80 vol% after the heat treatment.

When the piezoelectric single crystal and polycrystalline ceramic particles are mixed and heat treated, both single crystal and polycrystalline ceramic particles grow and increase in size during the heat treatment, and the degree of growth may vary depending on the heat treatment conditions, thereby controlling the physical properties after heat treatment.

In this case, the heat treatment temperature and time are the most important variables in the heat treatment conditions, and additional variables such as heat treatment atmosphere (eg, oxygen partial pressure), temperature increase rate and pressure are applied.

Therefore, depending on the heat treatment conditions, the grain growth rate and density will change, so the piezoelectric and mechanical properties will be different.

However, the optimum heat treatment conditions may vary depending on the composition of the piezoelectric single crystal and the ceramic. Preferably, the heat treatment temperature and time is performed at 900 to 1,300° C. for 1 to 100 hours for the heat treatment time.

In addition, the heat treatment is preferably performed at a temperature increase rate of 1 to 20 °C / min, the pressure during the heat treatment is performed at 1 to 50 MPa, but will not be limited thereto.

Furthermore, according to the present invention, a piezoelectric single crystal-polycrystalline ceramic composite can be obtained by mixing and heat-treating the perovskite-type piezoelectric single crystal having the composition formula of Formula 1 at a specific particle size distribution ratio between the polycrystalline ceramic particles.

The obtained piezoelectric single crystal-polycrystalline ceramic composite maintains the high piezoelectric charge constant and low dielectric loss of the piezoelectric single crystal, so that the piezoelectric charge constant [d ₃₃ (pC/N)] and the dielectric loss [tand] are maintained at room temperature. (%)]) satisfies the ratio [= d ₃₃ /tand] of 1,000 or more.

In addition, the piezoelectric single crystal-polycrystalline ceramic composite obtained by the present invention maintains the high piezoelectric charge constant and low dielectric loss of the piezoelectric single crystal, and the dielectric constant does not increase significantly, so that the piezoelectric charge constant (Piezoelectric Charge Constant, d ₃₃ , pC/N )]), the ratio of Piezoelectric Voltage Constant (g ₃₃ , ⅹ10 ^-3 Vm/N)]) to Dielectric Loss [tand (%)]) [= (d ₃₃ xg ₃₃ )/tand] meets 25,000 or more.

In addition, the piezoelectric single crystal-polycrystalline ceramic composite obtained by the present invention is

(1) The dielectric constant at 30℃ is 3,000 or more,

(2) Piezoelectric Charge Constant [d ₃₃ ] at 30°C of 1,200 pC/N or more and

(3) The first phase transition temperature at 30℃ or higher meets 80℃ or higher.

Furthermore, the present invention provides a high dielectric constant (K ₃ ^T ≥ 3,000), a piezoelectric charge constant (d ₃₃ ≥ 1,200 _pC /N), and a coercive field (EC ≥ 3 to 4) by including piezoelectric single crystals having a perovskite-type crystal structure. kV/cm) and a high internal electric field (E _I ≥0.5 to 1.0 kV/cm).

Specifically, the piezoelectric application parts include an ultrasonic transducer (a medical ultrasonic diagnostic device, a sonar transducer, a transducer for non-destructive testing, an ultrasonic cleaner, an ultrasonic motor, etc.), a piezoelectric actuator (d ₃₃ actuator, d ₃₁ actuator, d ₁₅ -type actuators, piezoelectric actuators for micro-position control, piezoelectric pumps, piezoelectric valves, piezoelectric speakers, bimorph-type actuators and stacked actuators, etc.), piezoelectric sensors (piezoelectric accelerometers, etc.) and piezoelectric polymer composites (piezoelectric single-crystal-polycrystalline ceramic composites and polymers, etc.) complex of ) and the like.

In addition, the dielectric application components include high-efficiency capacitors, infrared sensors, dielectric filters, electric field radiation transducers and electric field-vibration radiation transducers. etc.

Hereinafter, the present invention will be described in more detail through examples.

These examples are for explaining the present invention in more detail, and the scope of the present invention is not limited to these examples.

<Example 1> Piezoelectric single crystal-polycrystalline ceramic composite fabrication and characteristic evaluation 1

A piezoelectric single crystal having a composition of [Pb _0.965 Sr _0.02 La _0.01 ][(Mg _1/3 Nb _2/3 ) _0.4 Zr _0.25 Ti _0.35 ]O ₃ was prepared by the solid-state single crystal growth method. In addition, an excess of MgO was added in the powder synthesis process so that 2 vol% of the MgO secondary phase and the pore-enhanced phase were included in the prepared single crystal. At this time, as a result of evaluating the piezoelectric charge constant, dielectric constant and dielectric loss characteristics of the prepared (001) piezoelectric single crystal, the piezoelectric charge constant (d ₃₃ ) is 2,650 [pC/N], the dielectric constant is 8,773, and the dielectric loss (tan d) was 0.5%.

The prepared [Pb _0.965 Sr _0.02 La _0.01 ][(Mg _1/3 Nb _2/3 ) _0.4 Zr _0.25 Ti _0.35 ]O ₃ composition piezoelectric single crystal was cut into small sizes and then continuously through a ball milling process. was crushed with The final pulverized piezoelectric single crystal particles were sorted by size through a sieving process. By controlling the ball milling process conditions, time, and sieving conditions, piezoelectric single crystal particles having a size of several tens of μm to several mm were prepared.

The prepared piezoelectric single crystal particles and calcined ceramic powder having a particle size of ∼1 μm were mixed, molded and sintered to finally prepare a piezoelectric single crystal-polycrystalline ceramic composite. By controlling the volume of the piezoelectric single crystal in the mixing step of the piezoelectric single crystal particles and the calcined ceramic powder, a single crystal-polycrystalline ceramic composite having various volume fractions as shown in FIG. 2 was prepared.

<Example 2> Piezoelectric single crystal-polycrystalline ceramic composite fabrication and characteristic evaluation 1

A piezoelectric single crystal having a composition of [Pb _0.965 Sr _0.02 Sm _0.01 ][(Mg _1/3 Nb _2/3 ) _0.25 (Ni _1/3 Nb _2/3 ) _0.10 Zr _0.30 Ti _0.35 ]O ₃ was prepared by the solid-state single crystal growth method. . In addition, during the single crystal growth, pores on the polycrystal matrix were trapped inside the single crystal, and the prepared single crystal contained about 1.5% by volume of the pore-enhanced phase. The piezoelectric charge constant (d ₃₃ ) of the prepared piezoelectric single crystal was 4,457 [pC/N], the dielectric constant was 14,678, and the dielectric loss (tan d) was 1.0%.

Except for using the above-prepared [Pb _0.965 Sr _0.02 Sm _0.01 ][(Mg _1/3 Nb _2/3 ) _0.25 (Ni _1/3 Nb _2/3 ) _0.10 Zr _0.30 Ti _0.35 ]O ₃ composition piezoelectric single crystal , Piezoelectric single crystal particles and a piezoelectric single crystal-polycrystalline ceramic composite were prepared in the same process as in Example 1.

The Zr content of the prepared piezoelectric single crystal-polycrystalline ceramic composite was adjusted to be lower in the polycrystalline ceramic than in the piezoelectric single crystal. At this time, when the Zr content is low, the sintering temperature of the polycrystalline ceramic can be lowered, and the piezoelectric single crystal is heat treated at a lower temperature to minimize the chemical reaction between the piezoelectric single crystal and the polycrystalline ceramic particles, and thermal shock generated during the heat treatment process can be reduced. The advantage is that it can be minimized.

<Experimental Example 1> Evaluation of dielectric and piezoelectric properties 1

Among the piezoelectric single crystal-polycrystalline ceramic composites prepared in Example 1, piezoelectric single crystals with an average particle size of ~300 μm-polycrystalline particles with an average particle size of ~10 μm were mixed and molded and sintered in the composite, the volume fraction [single crystal volume / ( By measuring the changes in the piezoelectric charge constant [d ₃₃ (pC/N)], the piezoelectric voltage constant [g ₃₃ (mVm/V)] and the dielectric loss [tan d(%)] according to the volume of single crystal + volume of polycrystal)] Table 1 shows.

In the single crystal-polycrystalline ceramic composite of Table 1, the piezoelectric charge constant [d ₃₃ (pC / N)], the piezoelectric voltage constant [g ₃₃ (mVm/V)] and the dielectric loss [tan d (%)] were measured and described in Table 2 below.

From the above results, [Pb _0.965 Sr _0.02 La _0.01 ][(Mg _1/3 Nb _2/3 ) _0.4 Zr _0.25 Ti _0.35 ]O ₃ A piezoelectric single crystal-polycrystalline ceramic composite fabricated using a piezoelectric single crystal composition of the existing piezoelectric polycrystal It showed a higher piezoelectric charge constant (d ₃₃ ) and a higher piezoelectric voltage constant (g ₃₃ ) than ceramics and at the same time a lower dielectric loss (tan d). In particular, the piezoelectric properties of the composite were maximized when the piezoelectric single crystal grain size and volume fraction and the single crystal/polycrystalline size ratio were specific (d ₃₃ > 1,000, d ₃₃ /tan d > 1,000, (d ₃₃ ⅹg ₃₃ )/tan d > 30,000).

In addition, when the volume ratio of the piezoelectric single crystal is less than 30% or exceeds 80%, improved piezoelectric and mechanical properties cannot be obtained compared to the polycrystal.

In particular, when the volume fraction of the single crystal exceeded 80%, the sintered density of the composite was low, and thus it was easily broken during machining, so that a measurement specimen could not be made, or electricity was energized during poling, or the piezoelectric properties tended to be sharply lowered.

<Experimental Example 2> Evaluation of dielectric and piezoelectric properties 2

Ag paste electrodes were applied on both sides of the piezoelectric single-crystal-polycrystalline ceramic composite prepared in Example 2, followed by polling, and then dielectric and piezoelectric properties were evaluated.

In the composite formed and sintered by mixing piezoelectric single crystal with an average particle size of ∼600 μm and polycrystalline particles with an average particle size of ∼8 μm among the prepared piezoelectric single crystal-polycrystalline ceramic composite, the volume fraction [single crystal volume / (single crystal volume + polycrystal volume) The changes in the piezoelectric charge constant [d ₃₃ (pC/N)], the piezoelectric voltage constant [g ₃₃ (mVm/V)] and the dielectric loss [tan d (%)] according to the volume)] were measured and listed in Table 3 below. did

Among the single crystal-polycrystalline ceramic composites of Table 3, the piezoelectric charge constant [d ₃₃ (pC / N)], the piezoelectric voltage constant [g ₃₃ (mVm/V)] and the dielectric loss [tan d (%)] were measured and described in Table 4 below.

From the above results, [Pb _0.965 Sr _0.02 Sm _0.01 ][(Mg _1/3 Nb _2/3 ) _0.25 (Ni _1/3 Nb _2/3 ) _0.10 Zr _0.30 Ti _0.35 ]O ₃ Fabricated using a single piezoelectric crystal composition The piezoelectric single-crystal-polycrystalline ceramic composite exhibited a higher piezoelectric charge constant (d ₃₃ ), a higher piezoelectric voltage constant (g ₃₃ ) and a lower dielectric loss (tan d) than conventional piezoelectric polycrystalline ceramics.

In particular, the piezoelectric properties of the composite were maximized when the size and volume fraction of the piezoelectric single crystal grains and the single crystal/polycrystalline size ratio were specific (d ₃₃ > 1,000, d ₃₃ /tan d > 1,000, (d ₃₃ ⅹg ₃₃ )/tan d > 30,000). When the volume ratio of the piezoelectric single crystal was too small (less than 30%) or too large (more than 80%), improved piezoelectric and mechanical properties could not be obtained compared to polycrystals. In particular, when the volume fraction of the single crystal exceeds 80%, the sintered density of the composite is low, so it is easily broken during machining, so that a measurement specimen cannot be made, or electricity is energized at the time of poling, or the piezoelectric properties are rapidly lowered.

<Experimental Example 3> Observation of dielectric properties change and phase transition according to temperature

Piezoelectric single crystals of PMN-PT and [Pb _0.965 Sr _0.02 La _0.01 ][(Mg _1/3 Nb _2/3 ) _0.4 Zr _0.25 Ti _0.35 ]O ₃ composition were prepared by solid-state single crystal growth method, respectively. In addition, the piezoelectric single crystal-polycrystalline ceramic composite prepared in Example 1 was selected as a sample, and changes in dielectric properties and phase transition according to temperature were observed for the piezoelectric single crystal and the piezoelectric single crystal-polycrystalline ceramic composite.

5 is the result of observing the change in dielectric properties and the phase transition phenomenon according to the temperature of the PMN-PT piezoelectric single crystal manufactured by the solid-phase single crystal growth method, and the dielectric constant of the PMN-PT single crystal is the phase transition between the ferrofluid phases at the Curie _temperature (TC ). higher than at the temperature (T _RT ).

6 is a graph showing the change in dielectric properties and the result of the phase transition phenomenon according to temperature for the [Pb _0.965 Sr _0.02 La _0.01 ][(Mg _1/3 Nb _2/3 ) _0.4 Zr _0.25 Ti _0.35 ]O ₃ piezoelectric single crystal prepared by the solid-phase single crystal growth method; In particular, it was confirmed that the dielectric constant was higher at the phase transition _temperature (T _RT ) between ferrofluid phases than at the Curie temperature (TC ).

7 is a piezoelectric single crystal-polycrystalline ceramic composite prepared in Example 1 using the [Pb _0.965 Sr _0.02 La _0.01 ][(Mg _1/3 Nb _2/3 ) _0.4 Zr _0.25 Ti _0.35 ]O ₃ piezoelectric single crystal; The dielectric constant at the phase transition temperature was significantly higher than the dielectric constant at room temperature [dielectric constant (@ T _RT )> 3 ⅹ dielectric constant (@ 30℃)] It was confirmed that the room temperature characteristics were significantly improved.

From the above results, similar to the piezoelectric single crystal, the piezoelectric single crystal-polycrystalline ceramic composite exhibits a phase transition between ferrofluid phases (rhombohedral phase and tetragonal phase, etc.) below the Curie _temperature (TC ), and the dielectric constant (K ₃ ^T ) is It was confirmed that the phase transition temperature between the ferrofluid phases was three times higher than that of room temperature.

Therefore, more preferably at the phase transition temperature between the ferrofluid phases Using a piezoelectric single crystal having a high dielectric constant is effective in improving the piezoelectric properties of the piezoelectric single crystal-polycrystalline ceramic composite.

<Experimental Example 4> Evaluation of mechanical properties

[Pb _0.965 Sr _0.02 La _0.01 ][(Mg _1/3 Nb _2/3 ) _0.4 Zr _0.25 Ti _0.35 ]O ₃ The piezoelectric single crystal of Example 1 prepared by using the piezoelectric single crystal prepared by the solid-state single crystal growth method - With respect to the sample of the polycrystalline ceramic composite, mechanical properties such as fracture strength and fracture toughness were compared and evaluated. At this time, the breaking strength values were measured by a four-point bending strength measurement method according to the ASTM method.

Among the piezoelectric single crystal-polycrystalline ceramic composites of Example 1 shown in Table 1 above, two composites having a volume fraction of 40% and 60% were selected as specimens, and the (001) piezoelectric single crystal specimen and fracture strength were compared. The results are shown in Table 5 below.

In addition, two composite specimens having single crystal sizes of 200 μm and 500 μm were selected from the piezoelectric single crystal-polycrystalline ceramic composite of Example 1 shown in Table 1 in Table 2, and the (001) piezoelectric single crystal specimen and fracture strength were compared. The results are shown in Table 6 below.

From the above results, [Pb _0.965 Sr _0.02 La _0.01 ][(Mg _1/3 Nb _2/3 ) _0.4 Zr _0.25 Ti _0.35 ]O ₃ Compared to the piezoelectric single crystal, the piezoelectric single crystal-polycrystalline ceramic composite has two times higher breaking strength and fracture strength. Toughness values were shown, and these values were similar to those of general piezoelectric polycrystalline ceramics.

Therefore, it was confirmed that the fracture strength and fracture toughness of the piezoelectric single-crystal-polycrystalline ceramic composite prepared in this Experimental Example increased by about 2 times compared to that of the piezoelectric single crystal.

In addition, in the piezoelectric single crystal-polycrystalline ceramic composite, the polycrystalline matrix phases surrounding the single crystal not only have higher mechanical properties than the single crystal themselves, but also serve to protect the single crystal from external mechanical impact, and consequently, the mechanical performance of the composite is greatly improved.

By compounding the above-mentioned single crystal with excellent piezoelectric properties and polycrystalline ceramic with excellent mechanical properties, a composite excellent in both properties could be manufactured while maintaining the high piezoelectric properties of the piezoelectric single crystal and improving the mechanical brittleness properties.

In the above, the present invention has been described in detail only with respect to the described embodiments, but it is obvious to those skilled in the art that various changes and modifications are possible within the scope of the technical spirit of the present invention, and it is natural that such variations and modifications belong to the appended claims.

Claims (26)

It is a composite in which piezoelectric single crystal and polycrystalline ceramic particles having a perovskite structure ([A][B]O ₃ ) are complexed,
The average particle size distribution (a) of the piezoelectric single crystal is 100 to 1,000 μm,
The average particle size distribution (b) of the polycrystalline ceramic particles is 2 to 20 μm,
The piezoelectric single crystal-polycrystalline ceramic composite having the particle size distribution ratio (a/b) of 20 to 100. The piezoelectric single crystal-polycrystalline ceramic composite according to claim 1, wherein the piezoelectric single crystal is contained in an amount of 30 to 80% by volume. The piezoelectric single crystal-polycrystalline ceramic composite according to claim 1, wherein the piezoelectric single crystals are oriented in a <001> or <011> crystal direction in the composite. The method of claim 1, wherein the piezoelectric single-crystal-polycrystalline ceramic composite is heated at room temperature.
(1) Dielectric Constant (K ₃ ^T ) of 3,000 or more;
(2) Piezoelectric Charge Constant (d ₃₃ ) of 1,200 pC/N or more and
(3) A piezoelectric single-crystal-polycrystalline ceramic composite, characterized in that the first-appearing phase transition temperature is 80° C. or higher. The method of claim 1, wherein the piezoelectric single-crystal-polycrystalline ceramic composite is
There is a phase transition between the ferrofluid phases below the Curie _temperature (TC ),
The piezoelectric single crystal-polycrystalline ceramic composite has a dielectric constant (K ₃ ^T ) of the piezoelectric single crystal-polycrystalline ceramic composite, characterized in that at least three times higher at a phase transition temperature between ferrofluid phases than at room temperature. The method of claim 1, wherein the piezoelectric single-crystal-polycrystalline ceramic composite is
At room temperature, the piezoelectric charge constant (d ₃₃ , pC/N) and
A piezoelectric single crystal-polycrystalline ceramic composite, characterized in that the ratio [d ₃₃ /tand] of the dielectric loss (Dielectric Loss, tand (%)) is 1,000 or more. The method of claim 1, wherein the piezoelectric single-crystal-polycrystalline ceramic composite is
Ratio of piezoelectric voltage constant (d ₃₃ , pC/N), piezoelectric voltage constant, g ₃₃ , 10 ^-3 Vm/N) and dielectric loss (tand%) at room temperature [(d ₃₃ ⅹg ₃₃ )/ tand] is 25,000 or more, a piezoelectric single crystal-polycrystalline ceramic composite. The piezoelectric single-crystal-polycrystalline ceramic composite according to claim 1, wherein a part or all of an empty space inside the piezoelectric single-crystal-polycrystalline ceramic composite is filled with a polymer. The piezoelectric single crystal-polycrystalline ceramic composite according to claim 1, wherein the Zr content is higher than that of the polycrystalline ceramic particles in the piezoelectric single crystal. [Claim 2] The piezoelectric single crystal-polycrystalline ceramic composite according to claim 1, wherein the piezoelectric single crystal has a compositional formula of the following Chemical Formula 1:
Formula 1
[A _1-(a+1.5b) B _a C _b ][(MN) _1-xy (L) _y Ti _x ]O _3-z
In the above formula,
A is Pb or Ba,
B is at least one selected from the group consisting of Ba, Ca, Co, Fe, Ni, Sn and Sr,
C is at least one selected from the group consisting of Co, Fe, Bi, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu,
L is a single or mixed form selected from Zr or Hf,
M is at least one selected from the group consisting of Ce, Co, Fe, In, Mg, Mn, Ni, Sc, Yb and Zn,
N is at least one selected from the group consisting of Nb, Sb, Ta and W,
0<a≤0.10, 0<b≤0.05, 0.05≤x≤0.58 and 0.05≤y≤0.62 and 0≤z≤0.02. 11. The piezoelectric single-crystal-polycrystalline ceramic composite according to claim 10, wherein 0.01≤a≤0.10 and 0.01≤b≤0.05 in the above formula. The piezoelectric single-crystal-polycrystalline ceramic composite according to claim 10, wherein a/b≥2 in the above formula. 11. The piezoelectric single-crystal-polycrystalline ceramic composite according to claim 10, wherein 0.10≤x≤0.58 and 0.10≤y≤0.62 in the above formula. The piezoelectric single crystal-polycrystalline ceramic composite according to claim 10, wherein when L is a mixed form in the piezoelectric single crystal, it has a compositional formula of Formula 2 or Formula 3:
Formula 2
[A _1-(a+1.5b) B _a C _b ][(MN) _1-xy (Zr _1-w , Hf _w ) _y Ti _x ]O ₃
Formula 3
[A _1-(a+1.5b) B _a C _b ][(MN) _1-xy (Zr _1-w , Hf _w ) _y Ti _x ]O _3-z
In the above, A, B, C, M, N, a, b, x, y and z are the same as in Chemical Formula 1, provided that 0.01≤w≤0.20. The piezoelectric single crystal-polycrystalline ceramic composite according to claim 10, further comprising a reinforced secondary phase (P) in an amount of 0.1 to 20% by volume in the piezoelectric single crystal composition. The piezoelectric single crystal-polycrystalline ceramic composite according to claim 15, wherein the reinforced secondary phase P is a metal phase, an oxide phase, or a pore. The piezoelectric single crystal-polycrystal of claim 16, wherein the reinforced secondary phase P is at least one selected from the group consisting of Au, Ag, Ir, Pt, Pd, Rh, MgO, ZrO ₂ and pores. ceramic composite. 18. The piezoelectric single crystal-polycrystalline ceramic composite according to claim 17, wherein the reinforced secondary phase P is uniformly distributed in the form of particles in the piezoelectric single crystal or is regularly distributed while having a constant pattern. A single crystal particle (a) is prepared by pulverizing a piezoelectric single crystal of a perovskite structure ([A][B]O ₃ ) to 50 μm or more,
Prepare polycrystalline powder particles (b) with an average particle size distribution of 0.1 to 5 μm, mix and heat-treat with a particle size distribution a/b of 20 or more,
Growing the piezoelectric single crystal to a particle size of 100 μm or more by the heat treatment,
A method for producing a piezoelectric single-crystal-polycrystal ceramic composite, wherein the particle size distribution a/b after heat treatment is 20 to 100. 20. The method of claim 19, wherein the piezoelectric single crystal contains 80 vol% or less of the piezoelectric single crystal at the time of mixing. 20. The method of claim 19, wherein the piezoelectric single crystal is contained in an amount of 30 to 80 vol% after the heat treatment. The method according to claim 19, wherein the average particle size distribution (a) of the grown piezoelectric single crystal after the heat treatment is 100 to 1,000 μm, and the average particle size distribution (b) of the grown polycrystalline particles is 2 to 20 μm, and the particle size A method for producing a piezoelectric single-crystal-polycrystalline ceramic composite, characterized in that the distribution a/b is 20 to 100. The method of claim 19, wherein the heat treatment is performed at 900 to 1,300° C. for 1 to 100 hours. The method of claim 19, wherein the heat treatment is performed at a temperature increase rate of 1 to 20°C/min. 19. A piezoelectric application component and a dielectric application component comprising the piezoelectric monocrystalline-polycrystalline ceramic composite of any one of claims 1 to 18. 26. The method of claim 25, wherein the piezoelectric and dielectric applications include ultrasonic transducers, piezoelectric actuators, piezoelectric sensors, dielectric capacitors, and electric field radiation transducers. Field Generating Transducers) and electric field-piezoelectric application parts and dielectric application parts, characterized in that any one selected from the group consisting of Electric Field and Vibration Generating Transducers.

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