JP4491537B2 - Perovskite solid solution composition and piezoelectric ceramics obtained therefrom - Google Patents

Description

The present invention is in the form of potassium sodium niobate perovskite compound (NaNbO ₃₎ niobate (KNbO ₃₎ is the principal, this single pure oxides Paix composition added several mol% perovskite solid solution composition and the The present invention relates to a piezoelectric ceramic obtained by sintering a product.

  Piezoelectric ceramics cause elongation deformation when a voltage is applied. As actuators such as ultrasonic vibrators, ultrasonic motors, precision positioning elements, and piezoelectric transformers, piezoelectric ceramics generate voltage when they are deformed. Widely used as a sensor for piezoelectric gyroscopes, sonars, ultrasonic diagnostic elements, etc. Recently, there is an increasing tendency to make various machines and systems intelligent, and in particular, the importance of actuators is increasing. At present, the mainstream of piezoelectric ceramics that are widely used is mainly composed of lead zirconate titanate (PZT).

The piezoelectricity of this PZT ceramic is brought about by the combination of antiferroelectric lead zirconate (PbZrO ₃ ) with rhombohedral structure and ferroelectric lead titanate (PbTiO ₃ ) with tetragonal structure. The composition is highest in the vicinity of the phase boundary between the rhombohedral phase and the tetragonal phase (Morphotropic phase boundary, MPB, PbZrO ₃ / PbTiO ₃ = 52/48). Therefore, many PZT-based piezoelectric ceramics are used with a composition near the MPB. This is because instability is introduced into the perovskite structure and electrical sensitivity is increased, resulting in high electrical displacement.

In recent years, the momentum to use piezoelectric ceramics as an actuator for vibration control of aircraft, automobiles, railway vehicles, ships, etc. and vibration isolation of civil engineering buildings has increased. (ΔL / L) is at most 2 × 10 ⁻³ (0.2%) and the piezoelectric constant d ₃₃ of the longitudinal effect is about 300 to 600 pC / N, which is insufficient to meet such demands. Furthermore, development of a piezoelectric ceramic material exhibiting high displacement and high output characteristics is desired.

  On the other hand, recently, there has been a movement to reduce the amount of lead from various materials due to the problem of global environmental pollution, and piezoelectric ceramics are no exception. In fact, most of the currently used piezoelectric ceramics represented by PZT ceramics contain a large amount of lead. Europe is particularly serious about the lead problem, and it may soon be impossible to export lead-containing products from Japan to Europe. In view of such circumstances, currently, research and development of low lead-based or non-lead-based piezoelectric ceramic materials has been actively conducted in various fields. Lead-free piezoelectric ceramic materials have not been born.

To solve these problems, the present inventors have previously as a low lead-based piezoelectric _ceramics, and proposed NaNbO ₃ -KNbO ₃ -PbTiO ₃ based piezoelectric ceramic material (Patent Document 1).
This piezoelectric ceramic material exhibits excellent properties such as extremely high electrical displacement, despite the fact that the lead content is significantly reduced compared to conventional materials, but it still has a composition containing lead. Met.
Therefore, if an actuator material that is not low-lead but completely lead-free and exhibits the same or better characteristics as PZT ceramics can be obtained, environmental pollution problems can be improved, and an immeasurable economic ripple effect can be obtained. I can expect.

Japanese Patent Application No. 2003-040125

  The present invention is a further development of the proposal related to the above-mentioned Japanese Patent Application No. 2003-040125, which is completely lead-free, and is a leap forward compared to a piezoelectric material that has been put to practical use and is mainly made of PZT ceramics. An object of the present invention is to provide a novel environmentally friendly solid solution composition exhibiting high displacement characteristics and a piezoelectric ceramic obtained therefrom.

The present inventors have, as a goal to complete non-lead of NaNbO ₃ -KNbO ₃ -PbTiO ₃ based low lead piezoelectric ceramic filed earlier, closely studying about the effect of adding various oxides for NaNbO ₃ -KNbO ₃ results, even with the addition of non-lead perovskite such as BaTiO _3, SrTiO _3, CaTiO ₃ in place of PbTiO _3, further, if even using a simple oxide without a perovskite oxide using PbTiO ₃ As a result, the inventors have obtained the knowledge that an electrical displacement amount equal to or higher than that of the present invention can be obtained, and have completed the invention of this lead-free high-performance piezoelectric ceramic.
That is, according to the present invention, the following inventions are provided.
(1) Perovskite solid solution composition (1-z) (K _1-x Na _x ) NbO containing potassium perovskite sodium niobate (K _1-x Na _x ) NbO ₃ and trivalent metal oxide M3 ₂ O _{3 3} -zM3 ₂ O ₃ .
(Wherein, M3 represents a trivalent metal ions that enter the selective perovskite A or B-site, Bi, La, Y, Ce , Pr, Nd or et .x and z are chosen, 0.4 ≦ x ≦ respectively (Represents numerical values in the range of 0.6 and 0 <z ≦ 0.1.)
(2) The perovskite solid solution composition (1-z) (K _1-x Na _x ) NbO ₃ —zM3 ₂ O ₃ according to the above (1), wherein M3 is selected from Bi, La, and Y.
(3) A perovskite solid solution piezoelectric ceramic obtained by sintering the perovskite solid solution composition described in (1) or (2) above.
(4) The perovskite solid solution piezoelectric ceramic according to (3) above, which is densely sintered to a relative density of 95% or more.

  Piezoelectric ceramics according to the present invention not only dramatically improve electrical displacement over conventional materials typified by PZT, but also contain new lead as an environment-friendly high-performance piezoelectric ceramic material that does not contain lead. Open the way. The ceramics of the present invention, like PZT ceramics, are used as actuators such as ultrasonic transducers, ultrasonic motors, precision positioning elements, piezoelectric transformers, and sensors such as acceleration sensors, piezoelectric gyroscopes for car navigation systems, sonars, and ultrasonic diagnostic elements. In addition, new applications can be expected as actuators for vibration control of aircraft, automobiles, railway vehicles, ships, etc. and for vibration isolation of civil engineering buildings.

The present inventors, as described above, in Japanese Patent Application No. 2003-040125 Patent _invention has been proposed NaNbO ₃ -KNbO ₃ -PbTiO ₃ based low lead piezoelectric ceramic, the subsequent examination, the low lead-based piezoelectric ceramics It has been found that the excellent electrical displacement characteristics are given for the following reasons.

When PbTiO ₃ is added to a NaNbO ₃ -KNbO ₃ perovskite, a part of the A site ion (Na ⁺ , K ⁺ ), such as (Na ⁺ , K ⁺ , Pb ²⁺ ) (Nb ⁵⁺ , Ti ⁴⁺ ) O ₃ There in ^{Pb 2+,} part of B site ions ^{(Nb 5+)} is perovskite replaced by ^{Ti 4+.} At this time, Pb ²⁺ and Ti ⁴⁺ have different ion sizes and valences compared to the original ions, so that instability is introduced into the crystal lattice and the size of the formed ferroelectric domain is reduced. When the size of the ferroelectric domain is reduced, the ferroelectric domain is easily rotated by the applied electric field, so that the electric field induced strain is also increased. The reason why the NaNbO ₃ —KNbO ₃ —PbTiO ₃ high-density sintered body exhibits high piezoelectricity is thought to be due to such a change in the properties of the domain structure.

That is, the electric field induced strain characteristics of the ferroelectric ceramics are affected by the ease of rotation of the ferroelectric domain, and the electric field induced strain increases as the ease of rotation increases. Therefore, the oxide added to NaNbO ₃ -KNbO ₃ is not particularly limited to PbTiO _{3. If} the ion size or valence is different from that of Na ⁺ , K ⁺ , and Nb ⁵⁺ , NaNbO ₃ may be used. _The effect of improving the electric field induced strain characteristics of _3- KNbO ₃ is expected. Therefore, as a result of accumulating experimental examples in which non-lead perovskites such as BaTiO ₃ , SrTiO ₃ and CaTiO ₃ are added instead of PbTiO ₃ , the present inventors have concluded that the above hypothesis is correct. is there.
Even if not a perovskite oxide but a trivalent simple metal oxide is added, a difference in ion size and valence can be produced. When this simple oxide is added to the perovskite, the metal ion selectively enters either the A or B site of the perovskite lattice, but one of them becomes a lattice defect in terms of the balance of the valence. In any case, it was also confirmed that the addition of a simple oxide to NaNbO ₃ —KNbO ₃ has the same effect as the addition of a different perovskite.

The perovskite solid solution composition according to the reference example includes (i) perovskite-type potassium sodium niobate (K _1-x Na _x ) NbO ₃ and perovskite-type oxide M1M2O ₃ , and has the general formula (1-y) (K _{1 -x} Na _x) NbO ₃ - as a main component a mixed oxide represented by yM1M2O _3.
Here, M1M2O ₃ is a trivalent that can selectively enter a perovskite oxide or a perovskite oxide A site composed of a divalent M1 metal ion (excluding lead) and a tetravalent M2 metal ion. This represents a perovskite type oxide composed of M1 metal ions and trivalent M2 metal ions that can selectively enter perovskite type oxide B sites. x, y, and z represent numerical values in the range of 0.4 ≦ x ≦ 0.6, 0 <y ≦ 0.1, and 0 <z ≦ 0.1, respectively. However, the y range when M1 = Ba and M2 = Ti is 0 <y <0.05.
Specific examples of M1 include divalent or trivalent metal ions (excluding lead) that can selectively enter the perovskite A site. For example, Mg, Ca, Sr, Ba, Bi, La, Y Metal ions such as Ce, Pr and the like are exemplified, and among these, Ba, Sr, Ca and the like are preferable.
Specific examples of M2 include tetravalent or trivalent metal ions that can selectively enter the perovskite B site, and examples thereof include Ti, Zr, Sc, Ga, In, Zn, and Fe. And Zr are preferred.
The perovskite solid solution composition according to the present invention comprises (ii) a mixed oxide (1-z) comprising perovskite-type potassium sodium niobate (K _1-x Na _x ) NbO ₃ and a trivalent metal oxide M3 ₂ O _3. (K _1-x Na _x ) NbO ₃ -zM3 ₂ O ₃ is the main component.
Here, as the M3, a trivalent metal ions that enter the selective perovskite A or B-site, Bi, La, Y, Ce , Pr, Nd or al chosen, among others Bi, La, Y is preferably . x represents a numerical value in the range of 0.4 ≦ x ≦ 0.6.
In the above (i) and (ii), the perovskite type oxide M1M2O ₃ or the trivalent metal oxide M3 ₂ O ₃ is used in a perovskite type potassium sodium niobate (K _1-x Na _x ) NbO ₃ . It is 10 mol% or less with respect to it, Preferably it is 5 mol% or less.

The perovskite solid solution composition according to the present invention and the reference example is mainly composed of potassium sodium niobate (K, Na) NbO ₃ and 10 mol% or less of the other perovskite oxide (M1M2O ₃ ) or trivalent. It is obtained by adding a simple metal oxide (M3 ₂ O ₃ ).
As raw materials, various forms such as carbonates, oxalates, nitrates, hydroxides, oxides and the like can be used, and these raw materials are mixed in a predetermined composition to obtain a final composition. Can be prepared.

The perovskite solid solution composition of the present invention or the reference example can be made into a piezoelectric ceramic by densely sintering it preferably to a relative density of 95% or more.
Such a sintering means is not limited, but if it can be sintered under normal pressure, it will not exceed it. However, since the KNbO ₃ —NaNbO ₃ -based material is difficult to sinter, it is desirable to employ a pressure heating sintering method capable of sintering under pressure in order to efficiently obtain a high-density sintered body.

  As such pressure heating sintering method, spark plasma sintering method (Spark plasma sintering method, hereinafter referred to as SPS method), hot press (Hot press method, hereinafter referred to as HP method), anvil method, HIP method (thermal Among them, the methods preferably used in the present invention are the SPS method and the HP method.

  The SPS method is a technology in which a DC pulse current is applied to a specimen in a pressurized state, and high temperature plasma generated instantaneously by spark discharge is used to cause grain boundary diffusion and particle bonding. It is attracting attention as a high-speed sintering method.

In the SPS method, since the sintering is completed in a short time of approximately 15 minutes, including heating and holding _time, NaNbO ₃ -KNbO 3 system comprises large amounts of an easily volatile components (especially Na and K) as It is most preferable as a sintering method for materials in which composition fluctuation due to heating is a concern.

Incidentally, as seen in the previous Japanese Patent Application No. 2003-040125, as a result of applying the SPS method to the NaNbO ₃ —KNbO ₃ —PbTiO ₃ system, most of the composition was converted into a sintered body having a relative density of 96% or more. It has been demonstrated that the SPS method has a remarkable effect on densification, and that the piezoelectric displacement characteristics of the obtained ceramics are dramatically improved.

An example of a method for manufacturing the piezoelectric ceramic of the present invention or the reference example by the SPS method or the HP method will be described.
First, the main raw materials of K ₂ CO ₃ , Na ₂ CO ₃ and Nb ₂ O ₅ and the oxides as additives are blended to achieve the desired perovskite composition, and calcined and pulverized until a perovskite solid solution single phase is obtained. -Repeat the mixing process. Although the calcination conditions vary depending on the type and composition of the raw material, the temperature is usually 850 to 1000 ° C. and the time is 2 to 10 hours. The ceramic powder thus obtained is subjected to the SPS method or the HP method.

  What is necessary is just to perform SPS processing using apparatuses, such as the Sumitomo Coal Mining SPS-1030 type | mold apparatus, for example. Specifically, after a suitable amount of sample is filled in a graphite die, a desired sintered body can be obtained by applying a DC on / off pulse to the upper and lower punches in a vacuum while applying pressure with a graphite punch from above and below. It is done. In this SPS method, the sample reaches a predetermined temperature in about 5 minutes, and is sintered by holding the temperature for about 5 minutes. Although sintering temperature changes with compositions, it is the range of 1020-1100 degreeC. The obtained sintered body has a diameter of 15 mm and a thickness of 3 to 4 mm, and the relative density reaches 96% or more.

Moreover, what is necessary is just to perform HP method using apparatuses, such as the Tokyo Vacuum Co., Ltd. PRES-VAC-2 type apparatus. The HP method is the same as the SPS method in that a sample is placed in a graphite die and pressed with an upper and lower punch, but heating is performed by an external heater attached around the die.
First, an appropriate amount of the calcined ceramic powder is filled in a graphite die, and then evacuated, and heated by energizing an external heater while applying pressure with a graphite punch from above and below. In this hot press method, a predetermined temperature (1100 ° C.) is reached in about 2 hours, and a sintered body having a relative density of 95% or more can be obtained by maintaining the temperature for about 5 to 10 minutes.

  Note that since both the SPS method and the HP method use a graphite die in a vacuum, the sintered body is inevitably reduced to some extent, and is obtained by blackening with the inclusion of a reducing component. Thereafter, in an oxygen atmosphere, for example, 950 It is whitened by annealing at 5 ° C. for about 5 hours.

Both the SPS method and the HP method are effective means for obtaining high-density ceramics that cannot be achieved by the atmospheric pressure method. However, the HP method is somewhat concerned about the compositional variation of the sample because of the long temperature rise / fall time. The Incidentally, as a result of chemical analysis of the NaNbO ₃ —KNbO ₃ —PbTiO ₃ -based ceramics [1] obtained by the SPS method, it has also been confirmed that there is no significant variation between the charged composition and the final product composition.

Hereinafter, the present invention will be described in more detail with reference to Examples and Reference Examples .
The perovskite solid solution compositions of the present invention and reference examples were sintered using the above SPS apparatus and HP apparatus. The obtained ceramic was cut into a 5 mm × 5 mm × 0.5 mm size plate and subjected to mirror polishing on both sides, and then a gold sputtered film was attached to make an electrode to evaluate piezoelectric characteristics. Next, after polarization treatment was performed at room temperature under the condition of 30 kV / cm, the relationship between the applied voltage and the electric displacement was examined using a laser displacement meter.

Table 1 shows the composition, manufacturing method, and sintered density of the perovskite ceramics of the present invention and reference examples , and Table 2 shows the phase transition temperature t _c , relative permittivity, dielectric loss, and electromechanical coupling coefficient kp of the perovskite ceramics of the reference examples. , Shows frequency constant Nr, maximum strain.
The relative density of the ceramics obtained varies slightly depending on the composition and manufacturing method, but 96% or more was obtained in most samples. Both the SPS method and the HP method increase the density of the ceramic of the present invention. It proved to be effective as a means.

Reference examples 1-3
This group of reference examples relates to ceramics obtained by SPS treatment of BaTiO ₃ added at 1, 2 and 4 mol% to the (Na _0.5 K _0.5 ) NbO ₃ composition. Displacement at 80 kV / cm, respectively, 0.9%, 0.6%, a high value of 0.6%, it is knowledge NaNbO ₃ -KNbO ₃ -BaTiO high performance piezoelectric be _three systems are able to form. It is also clear that the smaller the amount of BaTiO ₃ added, the higher the phase transition temperature t _c and the better the electromechanical coupling coefficient kp and the frequency constant Nr.

Reference examples 4-5
In these reference examples , ceramics were obtained by subjecting (Na _0.6 K _0.4 ) NbO ₃ or (Na _0.4 K _0.6 ) NbO ₃ composition to 2 mol% addition of BaTiO ₃ to HP treatment. It can be seen that the electrical displacement of the obtained ceramic shows a high value of 0.3% to 0.5%. Comparing the (Na _0.6 K _0.4 ) NbO ₃ base and the (Na _0.4 K _0.6 ) NbO ₃ base, it seems that the (Na _0.4 K _0.6 ) NbO ₃ base is somewhat higher.

Reference Examples 6-7
These relate to ceramics obtained by subjecting a (Na _0.4 K _0.6 ) NbO ₃ composition to SrTiO ₃ added at 2 and 8 mol% and subjected to HP treatment. The displacement at 80 kV / cm is 0.2%.

Reference examples 8-10
These relate to ceramics obtained by SPS treatment of 1,5,10 mol% of SrTiO ₃ added to the (Na _0.5 K _0.5 ) NbO ₃ composition. Displacement at 80 kV / cm is a value which is substantially comparable to that of PZT-based inferior as compared with the case of NaNbO ₃ -KNbO ₃ -PbTiO ₃ system and NaNbO ₃ -KNbO ₃ -PbTiO ₃ system. In Examples 8 to 10, the same results were obtained when Ca was introduced instead of Sr.

Reference Example 11-14
These relate to ceramics obtained by SPS treatment of (Na _0.5 K _0.5 ) NbO ₃ composition with BaZrO ₃ or SrZrO ₃ added. Maximum strain is in the range of _{0.2-0.4%, NaNbO 3 -KNbO 3 -BaTiO} 3 system or NaNbO ₃ -KNbO ₃ -SrTiO somewhat lower than ₃ system.

As described above, in Reference Examples 1 to 14, the effects of adding various perovskite oxides to the NaNbO ₃ —KNbO ₃ system have been shown. However, other perovskite compounds not shown in these reference examples are also based on the previous theory. Obviously, it shows the same effect as these.

Examples 1 to 4
In these examples, trivalent metal oxides La ₂ O ₃ and Bi ₂ O ₃ capable of selectively substituting the perovskite A-site with respect to the (Na _0.5 K _0.5 ) NbO ₃ composition were added, and by HP Made ceramics. The electric displacement of the obtained ceramics was in the range of 0.15 to 0.25%, which was a value almost comparable to that of the PZT system.

Claims (4)

Perovskite potassium sodium niobate oxide (K _1-x Na _x ) NbO ₃ and trivalent metal oxide M3 ₂ O ₃ perovskite solid solution composition (1-z) (K _1-x Na _x ) NbO ₃ -zM3 ₂ O ₃ .
(Wherein, M3 represents a trivalent metal ions that enter the selective perovskite A or B-site, Bi, La, Y, Ce , Pr, Nd or et .x and z are chosen, 0.4 ≦ x ≦ respectively (Represents numerical values in the range of 0.6 and 0 <z ≦ 0.1.) The perovskite solid solution composition (1-z) (K _1-x Na _x ) NbO ₃ -zM3 ₂ O ₃ according to claim 1, wherein M3 is selected from Bi, La, and Y.   A perovskite solid solution piezoelectric ceramic obtained by sintering the perovskite solid solution composition according to claim 1.   4. The perovskite solid solution piezoelectric ceramic according to claim 3, which is densely sintered to a relative density of 95% or more.