KR102663619B1 - Piezoelectric single crystal including internal bias electric field, manufacturing method thereof and use for piezoelectric and dielectric articles using the same - Google Patents

Abstract

The present invention includes an internal electric field It relates to a piezoelectric single crystal, a manufacturing method thereof, and piezoelectric and dielectric application components using the piezoelectric single crystal.
The piezoelectric single crystal of the present invention has a perovskite-type crystal structure ([A][B]O ₃ ) by controlling the composition of the [A] site ion and the [B] site ion and the oxygen partial pressure during heat treatment during the manufacturing process. Piezoelectric application components and dielectrics using piezoelectric single crystals with excellent properties are maintained while maintaining the inherent high dielectric constant and piezoelectric constant, while simultaneously meeting the high Internal Bias Electric Field (E _I ) characteristics essential for the electrical stability of piezoelectric single crystals. Application parts can be manufactured and used in a wide temperature range and operating voltage conditions.

Description

Piezoelectric single crystal containing internal electric field, manufacturing method thereof, and piezoelectric and dielectric application components using the same

The present invention includes an internal electric field This relates to a piezoelectric single crystal, its manufacturing method, and piezoelectric and dielectric application components using the same. In more detail, it relates to a high internal electric field (Internal Bias Electric Field) essential for the electrical stability of the piezoelectric single crystal while maintaining a high dielectric constant, a high piezoelectric constant, and a high coercive field. , E _I ≥0.5∼3.0 kV/cm) It relates to a piezoelectric single crystal with a novel perovskite-type crystal structure that simultaneously satisfies the same characteristics, its manufacturing method, and piezoelectric and dielectric application components using the same.

Piezoelectric single crystals with a perovskite-type crystal structure ([A][B]O ₃ ) exhibit significantly higher dielectric constants (K ₃ ^T ) and piezoelectric constants (d ₃₃ and k ₃₃ ) compared to existing piezoelectric polycrystalline materials. It is used in high-performance components such as piezoelectric actuators, ultrasonic transducers, piezoelectric sensors, and dielectric capacitors, and is also expected to be applied as a substrate material for various thin film devices.

Piezoelectric single crystals with a perovskite-type crystal structure developed to date 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 ), PMN-PInN-PT, PMN-PYbN-PT and BiScO ₃ -PbTiO ₃ (BS-PT). . These single crystals exhibit congruent melting behavior when melted, and have typically been manufactured using existing single crystal growth methods such as the flux method and Bridgman method.

However, 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. Shortcomings such as low phase transition temperatures (T _C and T _RT ), low coercive field (E _C ), and brittleness significantly limit the utility of piezoelectric single crystals.

In general, piezoelectric single crystals with a perovskite-type crystal structure are known to have the highest dielectric and piezoelectric properties in the region near the MPB (morphotropic phase boundary) composition, which is the phase boundary between the rhombohedral phase and the tetragonal phase.

However, piezoelectric single crystals with a perovskite-type crystal structure generally show the best dielectric and piezoelectric properties when in the rhombohedral phase, so the applications of rhombohedral piezoelectric single crystals are most active. Since it is stable only below the phase transition temperature (T _RT ), it can be used only below T _RT , which is the maximum temperature at which the rhombohedral phase can be stable. Therefore, when the T _RT phase transition temperature is low, the use temperature of the rhombohedral piezoelectric single crystal is lowered, and the manufacturing and use temperatures of piezoelectric single crystal application parts are also limited to T _RT or lower.

In addition, when the phase transition temperatures (T _C and T _RT ) and coercive field (E _C ) are low, piezoelectric single crystals are easily depoled and have excellent dielectric and piezoelectric properties under machining, stress, heat generation, and driving voltage. will be lost Therefore, piezoelectric single crystals with low phase transition temperatures (T _C and T _RT ) and low coercive fields (E _C ) have limited single crystal application component manufacturing conditions, use temperature conditions, and driving voltage conditions. For PMN-PT single crystals, typically T _C <150℃, T _RT <80℃ and E _C <2.5 kV/cm, and for PZN-PT single crystals, typically T _C <170℃, T _RT <100℃ and E _C <3.5 kV/cm. In addition, dielectric and piezoelectric application parts made from these piezoelectric single crystals are also limited in manufacturing conditions, use temperature range, use voltage conditions, etc., which has been an obstacle to the development and commercialization of piezoelectric single crystal application parts.

To overcome the shortcomings of piezoelectric single crystals, single crystals of new compositions such as PInN-PT, PSN-PT and BS-PT have been developed, and also mixed single crystal compositions such as PMN-PInN-PT and PMN-BS-PT have been developed. It is being studied.

However, in the case of these single crystals, the dielectric constant, piezoelectric constant, phase transition temperature, coercive field, and mechanical properties could not be improved at the same time, and piezoelectric single crystals with compositions containing expensive elements such as Sc and In as main components due to the high single crystal manufacturing cost. There are problems that hinder the practical use of single crystals.

The reasons why piezoelectric single crystals with a perovskite-type crystal structure, including PMN-PT, developed to date show a low phase transition temperature can be broadly divided into three. First, the relaxor, which is the main component along with PT; The phase transition temperature of PMN, PZN, etc.) is low.

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

Second, because the MPB that forms the boundary between the tetragonal phase and the rhombohedral phase is not perpendicular to the temperature axis but is gently inclined, the Curie temperature (T _C ) is required to raise the phase transition temperature (T _RT ) between the rhombohedral phase and the tetragonal phase. Because reduction is inevitable, it is difficult to simultaneously increase the Curie temperature (T _C ) and the phase transition temperature (T _RT ) between the rhombohedral phase and the tetragonal phase.

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

Furthermore, the Relaxor-PT series single crystals presented in Non-Patent Document 1 are mainly manufactured by existing single crystal growth methods such as the flux method and Bridgman method using a melting process. However, due to the single crystal manufacturing process, it is difficult to manufacture large single crystals with uniform composition and the manufacturing cost is high. Due to the high cost and difficulty in mass production, commercialization has not yet been successful.

In addition, compared to piezoelectric polycrystalline ceramics, piezoelectric single crystals generally exhibit a high piezoelectric constant (d ₃₃ ≥2,000∼4,000 pC/N), but have a low coercive field (E _C ≤2 kV/cm) and are easily depoled, making them electrically Due to low stability, practical use is limited. Accordingly, a method of increasing the coercive electric field of a piezoelectric single crystal has been proposed, but its effectiveness has been pointed out as still being low due to the problem that increasing the coercive field is accompanied by a decrease in piezoelectric properties.

Accordingly, as a result of efforts to improve the conventional problems, the present inventors designed a method to maintain high piezoelectric properties while maintaining the electrical stability of the piezoelectric single crystal by appropriately increasing the coercive field and internal electric field, In the perovskite-type crystal structure ([A][B]O ₃ ), by controlling the composition of the [A] site ions and [B] site ions and the oxygen partial pressure during heat treatment during the manufacturing process, the high dielectric constant and intrinsic piezoelectric single crystal The present invention was completed by confirming the physical properties that simultaneously satisfy the high internal electric field (E _I ) characteristics essential for the electrical stability of piezoelectric single crystals while maintaining the piezoelectric constant.

Republic of Korea Patent No. 0564092 (announced on March 27, 2006) Republic of Korea Patent No. 0743614 (announced on July 30, 2007)

IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, vol. 44, no. 5, 1997, pp. 1140-1147.

The object of the present invention is to include an internal electric field To provide a piezoelectric single crystal.

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

Another object of the present invention is to apply it to piezoelectric components or dielectric components using the piezoelectric single crystal.

In order to achieve the above-described object, the present invention provides a piezoelectric single crystal of a perovskite-type structure ([A][B]O ₃ ) including an internal electric field that satisfies the physical properties (1) to (4) below. do.

(1) Dielectric Constant (K ₃ ^T ) is 4,000 or more

(2) Piezoelectric Charge Constant (d ₃₃ ) is 1,400 pC/N or more

(3) Coercive Electric Field (E _C ) is 3.0 kV/cm or more and

(4) Internal Bias Electric Field (E _I ) is more than 0.5 kV/cm.

The piezoelectric single crystal of the perovskite-type structure ([A][B]O ₃ ) of the present invention increases the coercive field and internal electric field by controlling the composition of the [A] site ions and [B] site ions, thereby increasing the electric field of the piezoelectric single crystal. Maintains stability and high piezoelectric properties.

Accordingly, the first embodiment of the piezoelectric single crystal of the perovskite-type structure ([A][B]O ₃ ) of the present invention provides a piezoelectric single crystal having the composition formula (1) below.

Formula 1

[A _1-(a+1.5b) B _a C _b ][(MN) _1-xy (L) _y Ti _x ]O ₃

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 one or more 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 selected from Zr or Hf, alone or in mixed form,

M is at least one member 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, 0.05≤y≤0.62.

When L is in a mixed form, a piezoelectric single crystal having the composition formula (2) below 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

In the above, A, B, C, M and N are the same as in Formula 1, and a, b, x and y are also the same. However, it indicates 0.01≤w≤0.20.

In the piezoelectric single crystal having the composition formula (1) or (2) of the present invention, 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 or Formula 2 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 or Formula 2 of the present invention, it is more preferable to satisfy 0.10≤x≤0.58 and 0.10≤y≤0.62.

In addition, the piezoelectric single crystal having the composition formula of Formula 1 or Formula 2 of the present invention has a composition gradient inside the single crystal of 0.2 to 0.5 mol%, giving it the characteristic of uniformity.

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

The piezoelectric single crystal above has 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. .

In addition, the piezoelectric single crystal has a longitudinal electromechanical coupling coefficient (k ₃₃ ) of 0.85 or more and a coercive electric field (Ec) of 3.0 to 12 kV/cm.

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

The present invention is a method of manufacturing the above piezoelectric single crystal,

(a) reducing the number density of abnormal grains (number of abnormal grains/unit area) by adjusting the average size of matrix grains of the polycrystalline body having the above composition, and

(b) heat treating the polycrystal with a reduced number density of abnormal particles obtained through step (a) to grow abnormal particles.

As another manufacturing method, a method for manufacturing a piezoelectric single crystal is provided, in which the polycrystal is heat treated under conditions that reduce the number density of abnormal particles by controlling the average size of the matrix particles of the polycrystal having the above composition.

In the above, a single crystal can be obtained by continuing to grow only a small number of abnormal particles generated while the number density of abnormal particles in the polycrystal is reduced.

A method of manufacturing a piezoelectric single crystal can be provided by bonding a seed single crystal to the polycrystal before heat treatment of the polycrystal and continuing to grow the seed single crystal into the polycrystal during heat treatment. At this time, the average size (R) of the matrix particles of the polycrystalline body is 0.5 to 2 of the critical size at which abnormal particles are generated (the average size of matrix particles at which the number density of abnormal particles is “0 (zero),” R _c ). It is controlled within the ship size range (0.5R _c ≤R≤2R _c ).

The method for manufacturing the piezoelectric single crystal is to control the composition of the [A] site ions and the [B] site ions in a piezoelectric single crystal with a perovskite-type crystal structure ([A][B]O ₃ ), and to control the oxygen partial pressure during heat treatment during the manufacturing process. By controlling the piezoelectric single crystal, it is possible to sufficiently induce an internal electric field (Internal Bias Electric Field, E _I ) that is not present in a typical PMN-PT single crystal while maintaining the high dielectric constant, piezoelectric constant, and coercive field inherent in the piezoelectric single crystal, making it resistant to the external environment. Large new piezoelectric single crystals can be provided.

Furthermore, the present invention provides piezoelectric application components and dielectric application components using a piezoelectric material made of the piezoelectric single crystal with excellent properties or a piezoelectric material composed of a composite of the piezoelectric single crystal and a polymer.

Examples of the above piezoelectric and dielectric application components include ultrasonic transducers, piezoelectric actuators, piezoelectric sensors, dielectric capacitors, and electric field generating transducers. It can be applied to any one selected from the group consisting of Transducers and Electric Field and Vibration Generating Transducers.

The piezoelectric single crystal and piezoelectric single crystal application parts according to the present invention not only have excellent physical properties such as a dielectric constant (K ₃ ^T ) of 4,000 or more, a piezoelectric constant (d ₃₃ ) of 1,400 pC/N or more, and a coercive electric field (E _C ) of 3 kV/cm or more. It has the advantage of having a high internal electric field (E _I ≥0.5∼3.0 kV/cm), which is “essential for the electrical stability of piezoelectric single crystals,” allowing it to be used in a wide temperature range and operating voltage conditions.

In addition, it is possible to manufacture piezoelectric single crystals using a solid-phase single crystal growth method suitable for mass production of single crystals and to develop a single crystal composition that does not contain expensive raw materials, making it possible to commercialize piezoelectric single crystals.

Furthermore, the piezoelectric single crystal and piezoelectric single crystal application components according to the present invention make it possible to manufacture and use piezoelectric application components and dielectric application components using piezoelectric single crystals with excellent characteristics in a wide temperature range.

_Figure 1 _{shows [ Pb 0.98-1.5x Sr 0.02 La ​ ​ ​ ​} x=0.1;y=0) is a piezoelectric single crystal,
Figure _{2 shows [ Pb 0.98-1.5x Sr 0.02 La ​ ​ ​ ​} x=0.01; y=0.05) Piezoelectric single crystal [Single crystal growth atmosphere - Air; black due to Mn addition],
_Figure 3 _{shows [ Pb 0.98-1.5x Sr 0.02 La ​ ​ ​ ​} x=0.01; y=0.05) Piezoelectric single crystal [single crystal growth atmosphere - N ₂ -H ₂ ; black due to Mn addition],
Figure _{4 shows [ Pb 0.98-1.5x Sr 0.02 La ​ ​ ​ ​} x=0.01; y=0.05) Polarization-Electric Field graph for piezoelectric single crystal [single crystal growth atmosphere - Air],
Figure 5 is a polarization-electric field graph for a typical PMN-30PT piezoelectric single crystal (single crystal growth atmosphere - Air) manufactured by the solid-phase single crystal growth method;
Figure _{6 shows [ Pb 0.98-1.5x Sr 0.02 La ​ ​ ​ ​} x=0.01; y=0.1) This is a polarization-electric field graph for a piezoelectric single crystal [single crystal growth atmosphere - N ₂ -H ₂ ].

Hereinafter, the present invention will be described in detail.

The present invention provides a piezoelectric single crystal that maintains high piezoelectric properties while maintaining electrical stability of the piezoelectric single crystal by increasing the coercive field and internal electric field.

Accordingly, (1) the dielectric constant (K ₃ ^T ) is 4,000 or more

(2) Piezoelectric Charge Constant (d ₃₃ ) is 1,400 pC/N or more

(3) Coercive Electric Field (E _C ) is 3.0 kV/cm or more and

(4) Provides a piezoelectric single crystal with a perovskite-type structure ([A][B]O ₃ ) whose internal electric field (E _I ) satisfies 0.5 kV/cm or more.

More preferably, (1) the dielectric constant is maintained at 4,000 or more and (2) the piezoelectric charge constant [d ₃₃ ] is maintained at 1,400 pC/N or more, and (3) the coercive electric field [E _C ]) is 4.0 kV/cm or more and (4) Internal Electric Field (Internal Bias Electric Field [E _I ]) is to provide a piezoelectric single crystal that satisfies 1.0 kV/cm or more.

The dielectric constant and piezoelectric constant values are evaluated under the same temperature conditions at room temperature, and unless otherwise specified in the specification of the present invention, they mean the dielectric constant and piezoelectric constant values evaluated at 30°C.

In addition, the piezoelectric single crystal is characterized in that physical properties (1) to (4) are maintained at a temperature of 20 to 80 ° C.

The piezoelectric single crystal of the perovskite-type structure ([A][B]O ₃ ) increases the coercive field and internal electric field by controlling the composition of the [A] site ion and the [B] site ion, thereby improving the electrical stability of the piezoelectric single crystal. Maintains high piezoelectric properties.

Accordingly, the piezoelectric single crystal of the perovskite-type structure ([A][B]O ₃ ) of the present invention provides a piezoelectric single crystal having the composition formula (1) below.

Formula 1

[A _1-(a+1.5b) B _a C _b ][(MN) _1-xy (L) _y Ti _x ]O ₃

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 one or more 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 selected from Zr or Hf alone or in mixed form,

M is at least one member 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, 0.05≤y≤0.62.

In the piezoelectric single crystal having the above formula (1), it is preferable that the porosity in the single crystal is 0.5 vol% or more.

The piezoelectric single crystal having the composition formula of Formula 1 of the present invention has a perovskite-type crystal structure ([A][B]O ₃ ), [A] based on the tendency for piezoelectric properties to further increase as the chemical composition becomes more complex. Site ions are composed of complex compositions.

At this time, if we look specifically at the complex composition of the [A] site ion in the piezoelectric single crystal with the composition formula of Formula 1, it may be composed of [A _1-(a+1.5b) B _a C _b ], and the A composition is flexible or It contains a lead-free element, and in the embodiments of the present invention, the description is limited to a leaded piezoelectric single crystal where A is Pb, but it will not be limited thereto.

In the [A] site ion, 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, and more preferably In other words, lanthanide elements are used alone or in 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 composition or a mixture of one or more types including La and Sm, but will not be limited thereto.

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

Preferably, in the composite composition of the [A] site ion corresponding to the donor in the piezoelectric single crystal composition of Formula 1, 0.01≤a≤0.10 and 0.01≤b≤0.05 must be satisfied, and more preferably, a/ It satisfies b≥2. At this time, if a is less than 0.01, there is a problem that the perovskite phase is unstable, and if it exceeds 0.10, the phase transition temperature becomes too low, making actual use difficult, which is not desirable.

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

At this time, in the composite composition of the [A] site ion in the piezoelectric single crystal having the composition formula of Chemical Formula 1, an excellent dielectric constant can be realized when the composite composition is composed of only trivalent metal elements or divalent metal elements.

According to the generally known [A][MN]O ₃ -PbTiO ₃ -PbZrO ₃ phase diagram, a composition region showing excellent dielectric and piezoelectric properties is shown around the phase boundary (MPB) of the rhombohedral phase and the tetragonal phase. In the [A][MN]O ₃ -PbTiO ₃ -PbZrO ₃ phase diagram, the dielectric and piezoelectric properties are maximized at the phase boundary composition of the rhombohedral phase and the tetragonal phase, and as the composition moves away from the MPB composition, the dielectric and piezoelectric properties gradually decrease. In addition, when the MPB composition is within 5 mol% of the rhombohedral region, there is little decrease in dielectric and piezoelectric properties, maintaining very high dielectric and piezoelectric property values, and when the MPB composition is within 10 mol% of the rhombohedral region. Although the dielectric and piezoelectric properties decreased continuously, the dielectric and piezoelectric properties values were sufficiently high to be applied to dielectric and piezoelectric application components. When the composition changes from the MPB composition to the tetragonal region, the decrease in dielectric and piezoelectric properties occurs more rapidly than in the rhombohedral region. However, even when the composition is within 5 mol% or within 10 mol% in the tetragonal normal region, the dielectric and piezoelectric properties continuously decrease, but the dielectric and piezoelectric properties are sufficiently high to be applied to dielectric and piezoelectric application components.

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 MPB composition changes by 5 mol% from the rhombohedral phase to the tetragonal phase, the maximum values of x and y are 0.53 and 0.57, respectively (in other words, when x is the maximum, x: y = 0.53: 0.47, When y is the maximum, x: y = 0.43: 0.57). And when the composition changes by 10 mol% from the MPB composition to the rhombohedral and tetragonal regions, the maximum values of x and y are 0.58 and 0.62, respectively (in other words, when x is the maximum, x: y = 0.58: 0.42 and , when y is the maximum, x: y = 0.38: 0.62). High dielectric and piezoelectric properties were maintained within the range of 5 mol% in the rhombohedral and tetragonal regions of the MPB composition, and within the range of 10 mol% in the rhombohedral and tetragonal regions of the MPB composition. It exhibits sufficiently high dielectric and piezoelectric property values to be applied to dielectric and piezoelectric application components.

In addition, if the contents of PbTiO ₃ and PbZrO ₃ , that is, the x and y values are less than 0.05, the phase boundary between the rhombohedral phase and the tetragonal phase cannot be created, or the phase transition temperatures and coercive fields are too low, making it not suitable for the present invention.

Therefore, in the complex composition of the [B] site ion corresponding to the acceptor in the piezoelectric single crystal composition of Formula 1, x is preferably in the range of 0.05≤x≤0.58, and more preferably 0.10≤x. ≤0.58. At this time, if x is less than 0.05, the phase transition temperature (Tc and T _RT ), piezoelectric constant (d ₃₃ , k ₃₃ ), or coercive electric field (Ec) is low, and if x is more than 0.58, the dielectric constant (K ₃ ^T ) , This is because the piezoelectric constants (d ₃₃ , k ₃₃ ) or phase transition temperature (T _RT ) are low. Meanwhile, y preferably falls within the range of 0.05≤y≤0.62, and more preferably satisfies 0.10≤y≤0.62. The reason is that when y is less than 0.05, the phase transition temperature (Tc and T _RT ), piezoelectric constant (d ₃₃ , k ₃₃ ) or coercive field (Ec) is low, and when y exceeds 0.62, the dielectric constant (K ₃ ^T ) or This is because the piezoelectric constants (d ₃₃ , k ₃₃ ) are low.

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

In the above mixed form, a piezoelectric single crystal having the composition formula (2) below 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

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

At this time, if w is less than 0.01, there is a problem that the dielectric and piezoelectric properties are not maximized, and if w is more than 0.20, the dielectric and piezoelectric properties are drastically reduced, which is not desirable.

Regarding the piezoelectric single crystal having the composition formula of Formula 1 above, as a preferred example, the piezoelectric single crystal with a perovskite-type structure based on the embodiment is characterized by having the composition formula of Formula 3 below.

Formula 3

[Pb _1-(a+1.5b) Sr _a C _b ][(MN) _1-xy (Zr) _y Ti _x ]O ₃

In the above equation,

C is one or more 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,

M is at least one member 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,

0.02≤a≤0.10, 0.005≤b≤0.05, 0.35≤x≤0.58 and 0.05≤y≤0.62.

In addition, in the embodiment, in the composition of the piezoelectric single crystal having the composition of Formula 3, the composition ratio of the donor and the acceptor is limited, while maintaining the high dielectric constant, piezoelectric constant, and coercive field inherent in the piezoelectric single crystal, Although the result of effectively increasing the coercive field and internal electric field is explained, the composition and composition ratio are not limited thereto, and various variations and modifications may be made within the composition range of Formula 1.

In the composition of the piezoelectric single crystal, the corecive electric field and internal electric field are effectively increased by optimizing and controlling the donor content and the acceptor, preferably, the Mn content. This increases the stability of the piezoelectric single crystal when driven by an electric field and under mechanical load conditions. Therefore, piezoelectric properties can be maximized and stability can be increased at the same time.

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. If the electromechanical coupling coefficient is less than 0.85, the characteristics are similar to those of piezoelectric polycrystalline ceramics and the energy conversion efficiency is lowered. Not desirable.

The piezoelectric single crystal according to the present invention preferably has a coercive electric field (E _C ) of 3.0 kV/cm or more, more preferably 3.5 kV/cm or more, and most preferably 4 to 12 kV/cm, and the coercive electric field is 3.0 kV. If it is less than /cm, there is a problem that poling is easily removed when processing piezoelectric single crystals or when manufacturing or using piezoelectric single crystal application parts.

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

In addition, the piezoelectric single crystal having the composition formula of Formula 1 or Formula 2 of the present invention can provide a uniform single crystal with a composition gradient inside the single crystal of 0.2 to 0.5 mol%.

Lead zirconate (PbZrO ₃ ) not only has a high phase transition temperature of 230℃, but also has the effect of making MPB more perpendicular to the temperature axis, maintaining a high Curie temperature and maintaining a high rhombohedral phase and tetragonal phase transition temperature (T _RT ), it is possible to develop compositions with high Tc and T _RT at the same time.

This is because even when lead zirconate is mixed with a conventional piezoelectric single crystal composition, the phase transition temperature increases in proportion to the content of lead zirconate. Therefore, a piezoelectric single crystal with a perovskite-type crystal structure containing zirconium (Zr) or lead zirconate can overcome the problems of existing piezoelectric single crystals. In addition, zirconia (ZrO ₂ ) or lead zirconate is used as a main component in existing piezoelectric polycrystalline materials and is an inexpensive raw material, so the purpose of the present invention can be achieved without increasing the raw material price of single crystals.

On the other hand, perovskite-type piezoelectric single crystals containing lead zirconate do not show congruent melting behavior when melted, unlike PMN-PT and PZN-PT, but show incongruent melting behavior. Therefore, if it shows non-eutectic behavior, it is separated into liquid phase and solid phase zirconia (solid phase ZrO ₂ ) when the solid phase is melted, and the solid phase zirconia particles in the liquid phase interfere with single crystal growth, so general single crystal growth methods using the melting process, such as the flux method and Bridgman method, are used. It cannot be manufactured with

In addition, it is difficult to manufacture a single crystal containing a strengthened secondary phase using a general single crystal growth method using a melting process, and this has not yet been reported. This is because, above the melting temperature, the reinforced secondary phase is chemically unstable and reacts with the liquid phase, so it cannot maintain its independent secondary phase form and disappears. In addition, separation of the secondary phase and liquid phase occurs due to the difference in density between the secondary phase and the liquid phase within the liquid phase, making it difficult to manufacture a single crystal containing the secondary phase. Furthermore, the volume fraction, size, and The shape, arrangement, and distribution cannot be controlled.

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

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

Therefore, it is impossible to produce a piezoelectric single crystal with a composite composition in a perovskite-type crystal structure ([A][B]O ₃ ) using the conventional single crystal growth methods, such as the flux method and Bridgman method. 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 manufactured at 1 to 5 mol% or more during the manufacturing process, whereas in the solid-phase single crystal growth method of the present invention, the composition gradient inside the single crystal is 1 to 5 mol% or more. It can be manufactured with a uniform composition of 0.2 to 0.5 mol%.

Therefore, by the solid-phase single crystal growth method of the present invention, in the perovskite-type crystal structure ([A][B]O ₃ ) containing lead zirconate, the complex composition of the [A] site ion and the [B] site ion By growing piezoelectric single crystals uniformly even with complex compositions, the dielectric constant (K ₃ ^T ≥4,000∼15,000) and piezoelectric constant (d ₃₃ ≥1,400∼6,000 pC/N) and high coercive field are achieved compared to conventional piezoelectric single crystals. It is possible to provide a new piezoelectric single crystal with a significantly higher (E _C ≥ 4∼12 kV/cm).

In addition, it has a high internal electric field (E _I ) of 0.5 kV/cm or more, more preferably 0.5 to 3.0 kV/cm, which is essential for the electrical stability of the piezoelectric single crystal, allowing it to be used in a wide temperature range and operating voltage conditions. It has the advantage of enabling use in .

The method for manufacturing 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 Bridgman method.

Specifically, the method for manufacturing a piezoelectric single crystal according to the solid-phase single crystal growth method of the present invention is

(a) reducing the number density of abnormal grains (number of abnormal grains/unit area) by adjusting the average size of matrix grains of the polycrystalline body having the above composition, and

(b) heat-treating the polycrystalline body with a reduced number density of abnormal particles obtained through step (a) to grow abnormal particles.

As another manufacturing method, a method for manufacturing a piezoelectric single crystal is provided, in which the polycrystal is heat treated under conditions that reduce the number density of abnormal particles by controlling the average size of the matrix particles of the polycrystal having the above composition.

In the above, a single crystal can be obtained by continuing to grow only a small number of abnormal particles generated while the number density of abnormal particles in the polycrystal is reduced.

A method of manufacturing a piezoelectric single crystal can be provided by bonding a seed single crystal to the polycrystal before heat treatment of the polycrystal and continuing to grow the seed single crystal into the polycrystal during heat treatment.

The average size (R) of the matrix particles of the polycrystalline body is 0.5 to 2 times the critical size at which abnormal particles are generated (the average size of matrix particles at which the number density of abnormal particles is "0 (zero), R _c ). It is controlled within the range (0.5R _c ≤R≤2R _c ). At this time, when the average size of the matrix particles of the polycrystal is smaller than 0.5Rc (0.5Rc > R), the number density of abnormal particles is too high for single crystals to grow, and the average size of the matrix particles of the polycrystal is less than 2Rc. In the large case (2Rc <R), the number density of abnormal particles is "0", but the growth rate of the single crystal is too slow to produce a large single crystal.

In the method for manufacturing a piezoelectric single crystal of the present invention, the heat treatment can be performed by controlling the oxygen partial pressure. At this time, oxygen partial pressure control can be performed in air conditions, N ₂ atmosphere, or H ₂ -N ₂ atmosphere, and as the size of oxygen partial pressure in the atmosphere decreases, the dielectric constant and piezoelectric constant decrease continuously, but The physical properties of the electric field (E _C ) and internal electric field (E _I ) tend to increase.

Therefore, by controlling the atmosphere [size of oxygen partial pressure] during the single crystal growth heat treatment process, it is possible to induce a sufficiently large internal electric field (E _I ), which is not present in a typical PMN-PT single crystal, to manufacture a new piezoelectric single crystal with high resistance to the external environment. can do.

Furthermore, the present invention provides a piezoelectric body composed of the above piezoelectric single crystal alone or a composite of the above piezoelectric single crystal and a polymer.

The polymer is not particularly limited, but when epoxy resin is used as a representative example, it can be provided in a form that has high resistance to mechanical shock and is easy to machine.

Furthermore, the present invention can provide piezoelectric application components and dielectric application components using the piezoelectric material, and the piezoelectric application components include ultrasonic transducers (medical ultrasonic diagnostic devices, sonar transducers, non-destructive testing transducers, ultrasonic cleaners, ultrasonic motors, etc.), piezoelectric actuators (d ₃₃ type actuator, d ₃₁ type actuator, d ₁₅ type actuator, piezoelectric actuator for fine position control, piezoelectric pump, piezoelectric valve and piezoelectric speaker, etc.), piezoelectric sensors (piezoelectric accelerometer, etc.), electric field radiation transformer There are Electric Field Generating Transducers and Electric Field and Vibration Generating Transducers.

Additionally, dielectric application components include high-efficiency capacitors, infrared sensors, and dielectric filters.

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

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

<Example 1> Fabrication of piezoelectric single crystal with internal electric field 1

_By solid _{- phase single crystal growth method , [} Pb _0.98-1.5x Sr _{0.02 La} A piezoelectric single crystal with a composition of ≤x≤0.02 [Donor content]; 0.0≤y≤0.1 [Acceptor content] was manufactured.

In the powder synthesis process, an excessive amount of MgO and PbO were added so that the produced single crystal contained 2 vol% of the MgO secondary phase and pore-enhancing phase. First, as shown in Table 1 below, [Pb _0.98-1.5x Sr _0.02 La _x ][(Mg _1/3 Nb _2/3 ) _0.4-y (Mn _1/3 Nb _2/3 ) _y Zr _0.25 Ti _0.35 ] Ceramic powder with a composition of O ₃ (0.0≤x≤0.02, 0.0≤y≤0.1) was manufactured using the Columbite method. First, MgO and Nb ₂ O ₅ powder were mixed by ball milling and then calcined to prepare the MgNb ₂ O ₆ phase. Additionally, the raw material powders were mixed again in a fixed ratio and calcined to prepare perovskite phase powder. Mixed powders were prepared by adding an excess amount of PbO and MgO to the prepared powder. After the mixed powders were molded, they were pressed and molded at a hydrostatic pressure of 200 MPa, and the powder molded bodies were each heat-treated for up to 100 hours at 25°C intervals under various temperature conditions between 900°C and 1300°C.

As a condition under which the average size (R) of the matrix particles of a polycrystalline body can be adjusted to a size range (0.5R _c ≤R≤2R _c ) that is 0.5 to 2 times the critical size at which abnormal particles are generated, the excess PbO added is The amount was determined to be in the range of 10 to 20 mol%, and the heat treatment temperature was determined to be in the range of 1000 to 1200°C (primary sintering). A Ba(Ti _0.7 Zr _0.3 )O ₃ seed single crystal was placed on the polycrystal prepared in this way and heat treated (single crystal growth heat treatment), and the polycrystal composition was determined using the continuous growth of the seed single crystal into the polycrystal. A single crystal was prepared.

The average size (R) of the matrix particles of the polycrystalline body is at least 0.5 times the critical size at which abnormal particles are generated (the average size of matrix particles at which the number density of abnormal particles becomes "0 (zero), R _c )" 2 When adjusted to a smaller size range (0.5R _c ≤R ≤2R _c ), the seed single crystals continued to grow inside the polycrystal. In this example, when the amount of excess PbO and the heat treatment temperature were adjusted, the average size (R) of the polycrystalline matrix particles was adjusted to a size range of 0.5 to 2 times the critical size at which abnormal particles are generated. When the average size (R) of the matrix particles of the polycrystalline was adjusted to the range of 0.5R _c ≤R≤2R _c , during heat treatment, Ba(Ti _0.7 Zr _0.3 )O ₃ seed single crystal [Pb _0.98-1.5x Sr _0.02 La _x ][(Mg _1/3 Nb _2/3 ) _0.4-y (Mn _1/3 Nb _2/3 ) _y Zr _0.25 Ti _0.35 ]O ₃ (0.0≤x≤0.02; 0.0≤y≤0.1) inside polycrystalline By continuously growing, a single crystal with the same composition as a polycrystal was manufactured. At this time, the size of the grown single crystal was more than 20×20㎟.

As an example of the piezoelectric single crystal manufactured above, Figure 1 shows [Pb _0.98-1.5x Sr _0.02 La _x ][(Mg _1/3 Nb _2/3 ) _0.4-y (Mn _1/3 Nb _2/3 ) _y Zr _0.25 Ti _0.35 ]O ₃ (x=0.1; y=0) is a piezoelectric single crystal, and Figure 2 shows [Pb _0.98-1.5x Sr _0.02 La _x ][(Mg _1/3 Nb _2/3 ) _0.4-y (Mn _{1 /3} Nb _2/3 ) _y Zr _0.25 Ti _0.35 ]O ₃ (x=0.01; y=0.05) It is a piezoelectric single crystal. At this time, Figure 2 appears black due to the addition of Mn in the air phase of the single crystal growth atmosphere.

In addition, a piezoelectric single crystal can be manufactured by changing the oxygen partial pressure in the atmosphere during the primary sintering and single crystal growth heat treatment of the ceramic powder molded body. As an example, [Pb _0.98-1.5x Sr _0.02 La _x ][(Mg) in FIG. 3 _1/3 Nb _2/3 ) _0.4-y (Mn _1/3 Nb _2/3 ) _y Zr _0.25 Ti _0.35 ]O ₃ (x=0.01; y=0.05) A piezoelectric single crystal can be manufactured. At this time, black color was confirmed due to the addition of Mn in the single crystal growth atmosphere N ₂ -H ₂ .

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

_{[ Pb 0.98-1.5x Sr 0.02 La ​ ​ ​ ​ ​ ​} (0.0≤x≤0.02 [Donor content]; 0.0≤y≤0.1 [Acceptor content]) For piezoelectric single crystals of composition, the composition (change in x and y) of the piezoelectric single crystals shown in Table 1 and the ceramic shown in Table 2 The dielectric and piezoelectric properties of the manufactured piezoelectric single crystal were evaluated by controlling the oxygen partial pressure in the atmosphere during the primary sintering of the powder compact and single crystal growth heat treatment.

_{Specifically , the prepared [ Pb 0.98-1.5x Sr 0.02 La ​ ​} 0.0≤x≤0.02; 0.0≤y≤0.1) Dielectric constant, phase transition temperatures (T _C and T _RT ), piezoelectric constant, and coercive field (E) according to changes in x[Donor content] and y[Mn content] in a single crystal. Changes in the characteristics of _C ) and internal electric field (E _I ) were measured by the IEEE method using an impedance analyzer, etc., and are listed in Table 1 below.

As seen in Table 1, in the case of a piezoelectric single crystal (x=0.0, y=0.05) (Comparative Example 1), the piezoelectric charge constant, dielectric constant and dielectric loss characteristics were evaluated, and the piezoelectric charge constant (d ₃₃ ) is 1,600 [pC/N], the dielectric constant is 5,640, and the dielectric loss (tan d) is 0.4%, showing excellent dielectric and piezoelectric properties. At this time, the internal electric field (E _I ) was 0.4.

In addition, in the case of a (001) piezoelectric single crystal (x = 0.01, y = 0.0) single crystal (Comparative Example 2), 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%. At this time, the internal electric field (E _I ) was 0.

On the other hand, in the case of piezoelectric single crystals manufactured according to changes in x[Donor content] and y[Mn content], the dielectric constant and piezoelectric constant increase with an increase in x[Donor content], while the With the increase, the dielectric constant and piezoelectric constant decreased continuously, but the coercive electric field (E _C ) and internal electric field (E _I ) increased.

In addition, as shown in Table 1, in the piezoelectric single crystal of the present invention, when the values of x [Donor content] and y [Mn content] are above a certain value (x≠0.0 and y≠0.0), the dielectric constant and piezoelectric constant are general It was possible to significantly increase the coercive electric field (E _C ) and internal electric field (E _I ) while maintaining the same properties as PMN-PT single crystals. In particular, a new piezoelectric single crystal with high resistance to the external environment was developed by being able to induce a sufficiently large internal electric field (E _I ), which is not present in typical PMN-PT single crystals.

In addition, the physical properties shown in Table 2 are similar to those of the prepared [Pb _0.98-1.5x Sr _0.02 La _x ][(Mg _1/3 Nb _2/3 ) _0.4-y (Mn _1/3 Nb _2/3 ) _y Zr _0.25 Ti _0.35 ]O ₃ (x≤0.02; 0.0≤y≤0.1) This is the result of observing the change in physical properties of the piezoelectric single crystal according to the change in atmosphere [size of oxygen partial pressure] during the primary sintering and single crystal growth heat treatment process. .

As shown in Table 2, the dielectric constant and piezoelectric constant decreased continuously as the size of the oxygen partial pressure in the atmosphere decreased during the primary sintering and single crystal growth heat treatment process, but the coercive electric field (E _C ) and internal electric field (E _I ) increased.

This effect tended to increase as the values of x[Donor content] and y[Mn content] increased. Therefore, when a piezoelectric single crystal with a composition containing x [Donor content] and y [Mn content] is manufactured under conditions of low oxygen partial pressure, the dielectric constant and piezoelectric constant are maintained similar to those of a typical PMN-PT single crystal, while at the same time the coercive electric field ( E _C ) and internal electric field (E _I ) could be significantly increased.

From the above, the present invention can induce a sufficiently large internal electric field (E _I ), which is not present in a typical PMN-PT single crystal, through controlling the atmosphere [size of oxygen partial pressure] during the primary sintering and single crystal growth heat treatment process, thereby protecting the external environment from A new piezoelectric single crystal with high resistance was developed.

_{From the above results , [ Pb 0.98-1.5x Sr 0.02 La ​} x≤0.02; 0.0≤y≤0.1) Adjusts “x[Donor content], y[Mn content] and x/y ratio” in single crystal and at the same time atmosphere [size of oxygen partial pressure] during primary sintering and single crystal growth heat treatment process. When adjusting, it was possible to optimize the piezoelectric constant, coercive electric field (E _C ), and internal electric field (E _I ) of the manufactured piezoelectric single crystal. Therefore, unlike conventional PMN-PT or PIN-PMN-PT single crystals, piezoelectric single crystals containing an internal electric field (E _I ) of a certain ideal size (E _I > 0.5 or 1.0 kV/cm) have high piezoelectric properties that can be used in external environments. It showed characteristics of remaining stable despite changes in .

<Example 2> Fabrication of piezoelectric single crystal with internal electric field 2

Carry out the same process as Example 1, but [Pb _0.98-1.5x Sr _0.02 Sm _x ][(Mg _1/3 Nb _2/3 ) _0.25 (Ni _1/3 Nb _2/3 ) _0.10-y (Mn _{1 /3} Nb _2/3 ) _y Zr _0.30 Ti _0.35 ]O ₃ (0.0≤x≤0.02 [Donor content]; 0.0≤y≤0.1 [Acceptor content]) A piezoelectric single crystal was manufactured.

<Experimental Example 2> Dielectric and piezoelectric properties evaluation 2

[Pb _0.98-1.5x Sr _0.02 Sm _x ][(Mg _1/3 Nb _2/3 ) _0.25 (Ni _1/3 Nb _2/3 ) _0.10-y (Mn _1/3 Nb _{2 /3} ) _y Zr _0.30 Ti _0.35 ]O ₃ (0.0≤x≤0.02 [Donor content]; 0.0≤y≤0.1 [Acceptor content]) In the piezoelectric single crystal of the composition, the composition (x) in the piezoelectric single crystals shown in Table 3 and changes in y) and the dielectric and piezoelectric properties of the piezoelectric single crystal manufactured by controlling the oxygen partial pressure in the atmosphere during the primary sintering and single crystal growth heat treatment of the ceramic powder molded body shown in Table 4 were evaluated.

_{The above [ Pb 0.98-1.5x Sr 0.02 Sm ​ ​ ​ ​ ​} Ti _0.35 ]O ₃ (0.0≤x≤0.02; 0.0≤y≤0.1) Dielectric constant, phase transition temperatures (T _C and T _RT ), piezoelectric constant, coercive field (E _C ) and internal electric field (E _I) of piezoelectric single crystal ) The changes in characteristics were measured by the IEEE method using an impedance analyzer, etc., and are listed in Table 3 below.

As a result of evaluating the piezoelectric charge constant, dielectric constant and dielectric loss characteristics of the single crystal in Table 3 above, the solid-phase single crystal growth method yielded [Pb _0.98-1.5x Sr _0.02 Sm _x ][(Mg _1/3 Nb _2/3 ) _0.25 ( In a piezoelectric single crystal of the composition Ni _1/3 Nb _2/3 ) _0.10-y (Mn _1/3 Nb _2/3 ) _y Zr _0.30 Ti _0.35 ]O ₃ (0.0≤x≤0.02; 0.0≤y≤0.1), the composition In the case of (x=0.0, y=0.05) (Comparative Example 3) and in the case of composition (x=0.01, y=0.0) (Comparative Example 4), the piezoelectric charge constant (d ₃₃ ), dielectric constant and dielectric loss (tan d) The characteristics were confirmed to be excellent, but the internal electric field (E _I ) was low or not induced.

Therefore, as shown in Table 3, in the piezoelectric single crystal of the present invention, when the values of x[Donor content] and y[Mn content] are above a certain value (x≠0.0 and y≠0.0), the dielectric constant and piezoelectric constant are general It was confirmed that the coercive electric field (E _C ) and internal electric field (E _I ) can be significantly increased while maintaining the same properties as PMN-PT single crystals.

In particular, a new piezoelectric single crystal with high resistance to the external environment was developed by being able to induce a sufficiently large internal electric field (E _I ), which is not present in typical PMN-PT single crystals.

_The physical properties shown in Table 4 _{below are the} above _{- prepared [} Pb _0.98-1.5x Sr _{0.02 Sm 3} Nb _2/3 ) _y Zr _0.30 Ti _0.35 ]O ₃ (0.0≤x≤0.02; 0.0≤y≤0.1) In piezoelectric single crystals, changes in the atmosphere [magnitude of oxygen partial pressure] during the primary sintering and single crystal growth heat treatment process This is the result of observing changes in the physical properties of a piezoelectric single crystal.

As shown in Table 4, the dielectric constant and piezoelectric constant decreased continuously as the size of the oxygen partial pressure in the atmosphere decreased during the primary sintering and single crystal growth heat treatment process, but the coercive electric field (E _C ) and internal electric field (E _I ) increased.

This effect further increased as the values of x[Donor content] and y[Mn content] increased. When a piezoelectric single crystal with a composition containing x[Donor content] and y[Mn content] was manufactured under conditions of low oxygen partial pressure, It was confirmed that the coercive electric field (E _C ) and internal electric field (E _I ) can be significantly increased while maintaining the dielectric constant and piezoelectric constant similar to those of a typical PMN-PT single crystal.

Therefore, the present invention can induce a sufficiently large internal electric field (E _I ), which is not present in a typical PMN-PT single crystal, by controlling the atmosphere [size of oxygen partial pressure] during the primary sintering and single crystal growth heat treatment process, thereby providing resistance to the external environment. This allowed the development of a new large piezoelectric single crystal.

From the above results, [Pb _0.98-1.5x Sr _0.02 Sm _x ][(Mg _1/3 Nb _2/3 ) _0.25 (Ni _1/3 Nb _2/3 ) _0.10-y (Mn _1/3 Nb _2/3 ) _y Zr _0.30 Ti _0.35 ]O ₃ (0.0≤x≤0.02; 0.0≤y≤0.1) Controls “x[Donor content], y[Mn content] and x/y ratio” in single crystal and simultaneously performs primary sintering and single crystal When adjusting the atmosphere [size of oxygen partial pressure] during the growth heat treatment process, the piezoelectric constant, coercive field (E _C ), and internal electric field (E _I ) of the manufactured piezoelectric single crystal could be optimized. Unlike conventional PMN-PT or PIN-PMN-PT single crystals, piezoelectric single crystals containing an internal electric field (E _I ) of a certain ideal size (E _I > 0.5 or 1.0 kV/cm) have high piezoelectric properties that can be used in external environments. It showed characteristics of remaining stable despite changes in .

<Experimental Example 3> Observation of changes in internal electric field according to temperature changes

[Pb _0.98-1.5x Sr _0.02 La _x ][(Mg _1/3 Nb _2/3 ) _0.4-y (Mn _1/3 Nb _2/3 ) _y Zr _0.25 Ti _0.35 ]O ₃ (x = 0.01; y = 0.05) and a typical PMN-30PT piezoelectric single crystal were manufactured using a solid-phase single crystal growth method. A measurement sample with a size of "(001) 4ⅹ4ⅹ0.5(T)㎜" was produced using the above-prepared piezoelectric single crystals, and changes in coercive field (E _C ) and internal electric field (E _I ) with increase in temperature were observed. .

Figure _{4 shows [ Pb 0.98-1.5x Sr 0.02 La ​ ​ ​ 3} (x=0.01; y=0.05) This is a graph of changes in polarization of the electric field of a piezoelectric single crystal [single crystal growth atmosphere - Air], observing changes in the coercive field and internal electric field as the temperature increases from room temperature. did.

As a result, at 25℃, the coercive electric field (E _C ) and internal electric field (E _I ) were 4.4 and 1.0 kV/cm, respectively, and when the temperature increased to 80℃, the coercive electric field and internal electric field were 2.3 and 0.6kV/cm, respectively. decreased.

Figure 5 is a graph observing the polarization change with respect to the electric field of a typical PMN-30PT piezoelectric single crystal [single crystal growth atmosphere - air] manufactured by the solid-phase single crystal growth method. As the temperature increases at room temperature, the coercive electric field and the internal Changes in the electric field were observed.

As a result, the coercive field at 25°C was 2.5 kV/cm and no internal electric field was observed. And when the temperature increased to 80℃, the coercive field decreased significantly to 1.2 kV/cm.

From the above results, in Example 1 of the present invention, [Pb _0.98-1.5x Sr _0.02 La _x ][(Mg _1/3 Nb _2/3 ) _0.4-y (Mn _1/3 Nb _2/3 ) _y Zr _0.25 Ti _0.35 ]O ₃ (x=0.01; y=0.05) The piezoelectric single crystal [single crystal growth atmosphere - Air] has a coercive electric field about twice that of the general PMN-30PT piezoelectric single crystal [single crystal growth atmosphere - Air], especially including the internal electric field. It has the characteristic of doing so.

In addition, even when the temperature increases, the coercive field and internal electric field are maintained, showing the characteristic of maintaining the characteristics without depoling in response to temperature changes. _{In particular} , _{at 80 ° C , [ Pb 0.98-1.5x} Sr _{0.02 La} =0.01; y=0.05) The coercive electric field of the piezoelectric single crystal [single crystal growth atmosphere - Air] was similar to that of the PMN-30PT piezoelectric single crystal [single crystal growth atmosphere - Air] at room temperature, and the internal electric field was maintained, making it relatively high. It was confirmed to be stable.

<Experimental Example 4> Observation of changes in internal electric field according to temperature changes

_{In Example 1 , [ Pb 0.98-1.5x Sr 0.02 La ​ ​} =0.01; y=0.1) Piezoelectric single crystals were manufactured using a solid-phase single crystal growth method. During the manufacturing process, a measurement sample with a size of "(001) 4ⅹ4ⅹ0.5(T)㎜" was made using piezoelectric single crystals manufactured by controlling the oxygen partial pressure using N ₂ -H ₂ atmosphere during primary sintering and single crystal growth heat treatment. It was manufactured and changes in the coercive electric field (E _C ) and internal electric field (E _I ) were observed.

Figure _{6 shows [ Pb 0.98-1.5x Sr 0.02 La ​ ​ ​ ​} ; y=0.1) A graph of the polarization-electric field of a piezoelectric single crystal [single crystal growth atmosphere - N ₂ -H ₂ ], which has x[Donor content] and y[Mn content] above a certain size. It was confirmed that when a single crystal is manufactured under conditions of low oxygen partial pressure, the coercive electric field (E _C ) and internal electric field (E _I ) can be significantly increased to 5.6 and 2.8 kV/cm, respectively.

From the above, by controlling x [Donor content] and y [Mn content] in the piezoelectric single crystal composition and simultaneously controlling the atmosphere [size of oxygen partial pressure] during the primary sintering and single crystal growth heat treatment process, It was confirmed that the internal electric field (E _I ) could be induced sufficiently large.

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

Claims (18)

When growing a single crystal by the solid-phase single crystal growth method, the coercive field (E _C ) and internal electric field (E _I ) properties are controlled according to the oxygen partial pressure reduction conditions during heat treatment, and the following physical properties (1) to (4) are simultaneously satisfied,
Including an internal electric field, characterized in that the physical properties are maintained at a temperature of 20 to 80 ° C. Piezoelectric single crystal with perovskite-type structure ([A][B]O ₃ ):
(1) Dielectric Constant (K ₃ ^T ) is 4,000 or more
(2) Piezoelectric Charge Constant (d ₃₃ ) is 1,400 pC/N or more
(3) Coercive Electric Field (E _C ) is 3.0 kV/cm or more and
(4) Internal electric field (E _I ) is more than 0.5 kV/cm. delete The piezoelectric single crystal of claim 1, wherein the piezoelectric single crystal of the perovskite-type structure has the following formula:
Formula 1
[A _1-(a+1.5b) B _a C _b ][(MN) _1-xy (L) _y Ti _x ]O ₃
In the above equation,
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 one or more 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 selected from Zr or Hf, alone or in mixed form,
M is at least one member 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. The piezoelectric single crystal according to claim 3, wherein the single crystal has a porosity of 0.5 vol% or more. The method of claim 3, wherein in the formula
0.01≤a≤0.10,
A piezoelectric single crystal characterized by 0.01≤b≤0.05. The method of claim 3, wherein in the formula
A piezoelectric single crystal characterized by a/b≥2. The method of claim 3, wherein in the formula
A piezoelectric single crystal characterized by 0.10≤x≤0.58 and 0.10≤y≤0.62. The piezoelectric single crystal according to claim 3, wherein the single crystal has a porosity of 0.5 vol% or more. The piezoelectric single crystal according to claim 3, wherein the piezoelectric single crystal has a composition gradient inside the single crystal of 0.2 to 0.5 mol%. The piezoelectric single crystal according to claim 3, wherein x and y fall within a range of 10 mol% from the phase boundary (MPB) composition of the rhombohedral phase and the tetragonal phase. The piezoelectric single crystal according to claim 3, wherein x and y are within a range of 5 mol% from the phase boundary (MPB) composition of the rhombohedral phase and the tetragonal phase. (a) Reduce the number density (number of abnormal grains/unit area) of abnormal grains by adjusting the average size of matrix grains of the polycrystalline body having the composition constituting the piezoelectric single crystal according to clause 3. Steps and
(b) A method of producing a piezoelectric single crystal comprising the step of heat-treating the polycrystal with a reduced number density of abnormal particles obtained through step (a) to grow abnormal particles. The method of claim 12, wherein the average size (R) of the matrix particles of the polycrystal is a critical size at which abnormal particles are generated (the average size of matrix particles at which the number density of abnormal particles becomes "0 (zero)", R _c ) A method of manufacturing a piezoelectric single crystal, characterized in that it is adjusted to a size range of 0.5 to 2 times (0.5R _c ≤R≤2R _c ). The method of claim 12, wherein the coercive field (E _C ) and internal electric field (E _I ) properties are controlled according to oxygen partial pressure conditions during the heat treatment. The method of claim 14, wherein the coercive field (E _C ) and the internal electric field (E _I ) are increased as the oxygen partial pressure decreases. The method of claim 15, wherein the physical properties are
(1) Dielectric constant is 4,000 or more,
(2) Piezoelectric Charge Constant [d ₃₃ ] is maintained above 1,400 pC/N,
(3) Coercive Electric Field [E _C ]) is 4.0 kV/cm or more and
(4) A method of manufacturing a piezoelectric single crystal, characterized in that an internal electric field (Internal Bias Electric Field [E _I ]) of 1.0 kV/cm or more is implemented. Piezoelectric application components and dielectric application components using a piezoelectric material made of a single piezoelectric crystal according to any one of claims 1, 3 to 11 or a composite of the piezoelectric single crystal and a polymer. The method of claim 17, wherein the piezoelectric application components and dielectric application components include ultrasonic transducers, piezoelectric actuators, piezoelectric sensors, dielectric capacitors, and electric field radiation transducers. Piezoelectric application components and dielectric application components, characterized in that one selected from the group consisting of Field Generating Transducers and Electric Field and Vibration Generating Transducers.