CN114276134A

CN114276134A - Lead-free piezoelectric ceramic material with high-temperature stable electrostriction and preparation method thereof

Info

Publication number: CN114276134A
Application number: CN202011043061.8A
Authority: CN
Inventors: 刘志甫; 宋观华; 张发强; 李永祥; 刘峰
Original assignee: Suzhou Research Institute Shanghai Institute Of Ceramics Chinese Academy Of Sciences; Shanghai Institute of Ceramics of CAS
Current assignee: Suzhou Research Institute Shanghai Institute Of Ceramics Chinese Academy Of Sciences; Shanghai Institute of Ceramics of CAS
Priority date: 2020-09-28
Filing date: 2020-09-28
Publication date: 2022-04-05
Anticipated expiration: 2040-09-28
Also published as: CN114276134B

Abstract

The invention discloses a lead-free piezoelectric ceramic material with high-temperature stable electrostriction and a preparation method thereof. The chemical general formula of the leadless piezoelectric ceramic material is as follows: (0.93-x)(Bi_0.5Na_0.5)TiO₃‑0.06BaTiO₃‑0.01(K_0.5Na_0.5)NbO₃‑xSrTiO₃WhereinxAnd = 0.02-0.1. The temperature change rate of the maximum electrostriction and the normalized strain of the leadless piezoelectric ceramic material at the temperature of 25-120 ℃ is within 15 percent. The excellent temperature stability is good for SrTiO₃After solid solution, the ferroelectric-relaxation transition temperature of the material can be lowered below room temperature, so that the adverse effect of the phase transition on the temperature stability of the electrical strain of the material is significantly suppressed.

Description

Lead-free piezoelectric ceramic material with high-temperature stable electrostriction and preparation method thereof

Technical Field

The invention relates to a lead-free piezoelectric ceramic material with high-temperature stable electrostriction and a preparation method thereof, belonging to the technical field of lead-free piezoelectric ceramic materials.

Background

The piezoelectric material can realize the mutual conversion between electric energy and mechanical energy based on the electromechanical coupling effect, and is widely applied to the fields of precision control, piezoelectric drivers and the like by virtue of the characteristics of ultrahigh precision, ultrafast response and the like. Lead-based piezoelectric ceramics such as lead zirconate titanate (Pb (Zr, Ti) O₃PZT), etc., have long occupied the piezoelectric application market due to excellent piezoelectric and strain performance, less strain hysteresis, and good temperature stability. However, lead oxide (PbO) is highly toxic, and PbO content as high as 70% poses a great threat to human society and natural environment in the production, use and waste processes of lead-based piezoelectric ceramics. Therefore, the development of high-performance lead-free piezoelectric ceramic materials has become a focus of attention in the industry.

At present, the perovskite type lead-free piezoelectric material of major interest in the field of piezoelectric ceramics includes sodium bismuth titanate-based [ (Bi)_0.5Na_0.5)TiO₃，BNT]Potassium sodium niobate [ (K, Na) NbO₃，KNN]Radical and barium titanate (BaTiO)₃BT) based systems, etc., are considered to be very promising lead-free piezoelectric material systems. Among them, the BNT-BT-KNN ternary system has excellent ferroelectric piezoelectric performance, rich Morphotropic Phase Boundary (MPB) and higher Curie temperature (T)_c) The method arouses the interest of a great number of researchers, and the researchers develop a series of work in related systems and discover rich dielectric, ferroelectric and piezoelectric phenomena. In 2007, the field-induced strain output and the strain capacity which are comparable to those of lead-based materials at room temperature are obtained in a BNT-BT-KNN system by Zhang and the like of Nanjing universityUp to 0.45% (ZHANG S T, KOUNGA A B, AULBACH E, et al_0.5Na_0.5TiO₃-BaTiO₃-K_0.5Na_0.5NbO₃ system[J]Applied Physics Letters,2007,91(11):112906), since the study of the large strain BNT-based lead-free piezoelectric ceramics became a big hotspot. However, it should be noted that although the BNT-based lead-free piezoelectric ceramic has the potential to obtain high electrical strain, its coercive field is as high as 6-7 kV/mm, and obtaining large strain performance usually requires applying a large external electric field, which is easy to induce breakdown, heat generation, and other problems in the use process of the material. In addition, the acquisition of high-performance BNT-based lead-free piezoelectric ceramics is usually based on phase boundary regulation, and the performance design is realized by utilizing the characteristic that a ferroelectric domain near the phase boundary is easy to turn over under the action of electricity and force, but like other lead-free piezoelectric systems, the BNT system is difficult to design an MPB which is similar to PZT ceramics and is close to vertical, so that the performance of the material is remarkably changed along with the change of the use temperature, and the temperature stability of the strain performance is far inferior to that of the lead-based system, thereby seriously hindering the practicability of the material.

Disclosure of Invention

In view of the above problems, an object of the present invention is to provide a lead-free piezoelectric ceramic material with stable electrostrictive strain at high temperature, which has high compactness and stable electrostrictive strain at high temperature, and is thus expected to be used in the field of actuators with high requirements on temperature stability, and a method for preparing the same.

In a first aspect, the present invention provides a lead-free piezoceramic material having a high temperature stable electrostriction. The chemical general formula of the leadless piezoelectric ceramic material is as follows: (0.93-x) (Bi)_0.5Na_0.5)TiO₃-0.06BaTiO₃-0.01(K_0.5Na_0.5)NbO₃-xSrTiO₃. Wherein x is 0.02-0.1. x is SrTiO₃In percentage by mole. When x is less than 0.02, the coercive field of the lead-free piezoelectric ceramic material is large, and the temperature stability of the electrostriction is poor; when x is greater than 0.1, the amount of electrostriction of the lead-free piezoelectric ceramic material is limited due to its weak ferroelectricity. Preferably, x is 0.04 to 0.08.At the moment, the ferroelectric-relaxation ferroelectric phase transition temperature of the lead-free piezoelectric ceramic material is reduced to be lower than room temperature, and the adverse effect of phase transition on the stability of the electrostriction temperature is weakened, so that the material has excellent strain temperature stability. Also, SrTiO due to paraelectric phase₃The long program of the ferroelectric crystal lattice can be interrupted by the solid solution, so that the ferroelectric domain of the material is converted into a micro domain from a macro domain, and the micro domain is easier to turn over under an electric field, so that the driving electric field of the lead-free piezoelectric ceramic is lower than 5 kV/mm.

Preferably, the phase structure of the lead-free piezoceramic material is a trigonal-tetragonal phase coexisting structure. The structural characteristic enables the matrix to realize strain through electric domain inversion under an external electric field, and can also enhance the electric strain performance through electric field induced three-square phase transformation.

The lead-free piezoelectric ceramic material has smaller strain hysteresis. Strain hysteresis is the phenomenon of misalignment of the amount of strain in a piezoelectric material during the application and removal of a field, and is generally described in terms of the magnitude of strain hysteresis, which is defined as the ratio of the amount of strain lagging at half the maximum electric field to the amount of strain at the maximum electric field. Preferably, the strain hysteresis of the lead-free piezoceramic material is 11% -42%.

Preferably, the lead-free piezoceramic material is in a relaxed phase. High content of SrTiO₃The doping can obviously enhance the relaxation property of the system.

Preferably, the lead-free piezoelectric ceramic material exhibits a strain response characteristic approaching that of a linear dielectric between 25-120 ℃.

Preferably, the lead-free piezoelectric ceramic material has a temperature change rate of 15% or less of the maximum electrostriction and normalized strain at 25-120 ℃. Better temperature stability is beneficial to SrTiO₃After solid solution, the ferroelectric-relaxation transition temperature of the material can be lowered below room temperature, so that the adverse effect of the phase transition on the temperature stability of the electrical strain of the material is significantly suppressed.

In a second aspect, the present invention provides a method for preparing the lead-free piezoelectric ceramic material with high temperature stable electrostriction, which comprises the following steps:

1) according to (0.93-x) (Bi)_0.5Na_0.5)TiO₃-0.06BaTiO₃-0.01(K_0.5Na_0.5)NbO₃-xSrTiO₃In the stoichiometric ratio of Bi, Na, Ba, K, Nb, Sr and Ti elements, each raw material Bi is weighed₂O₃、Na₂CO₃、BaCO₃、K₂CO₃、Nb₂O₅、SrCO₃And TiO₂Uniformly mixing the raw materials to form mixed slurry; drying, grinding and sieving the mixed slurry to obtain mixed powder;

2) presintering the mixed powder at 750-950 ℃, preserving heat for 1-4 h, cooling to room temperature along with a furnace, performing secondary ball milling, drying, grinding and sieving to obtain (BNT-BT-KNN) -xST powder;

3) pressing and forming the (BNT-BT-KNN) -xST powder prepared in the step 2) to form a blank;

4) sintering the blank prepared in the step 3) at 1150-1200 ℃ for 2-5 h, and then cooling to room temperature along with a furnace to prepare the lead-free piezoelectric ceramic material with high-temperature stable electrostriction.

Preferably, in the step 2), the pre-sintering temperature is 800-.

Preferably, in the step 2), the particle size of the (BNT-BT-KNN) -xST powder is 0.05-2.0 μm.

Preferably, in the step 3), a binder is added into the (BNT-BT-KNN) -xST powder before compression molding, and the mixture is granulated and sieved; preferably, the binder is polyvinyl alcohol with the mass fraction of 4-8%, and the addition amount of the binder is 5% -10% of the mass of the (BNT-BT-KNN) -xST powder.

Preferably, in the step 4), the blank is subjected to heat preservation at 450-650 ℃ for 0.5-3 h before sintering so as to perform plastic removal on the blank.

Preferably, in the step 4), the sintering temperature is 1150-1180 ℃, and the sintering heat preservation time is 3-4 h.

Compared with the prior art, the invention has the following beneficial effects:

1. by small amounts of SrTiO₃Solid solution doping, can electrically strain the material at room temperature under the drive electric field of 5kV/mmThe amount is increased from-0.13% to-0.20%; the strain change rate of the material is below 15% at 25-120 ℃; the optimal strain hysteresis of the material is realized by 11 percent;

2. the chemical composition disclosed by the invention is (0.93-x) (Bi)_0.5Na_0.5)TiO₃-0.06BaTiO₃-0.01(K_0.5Na_0.5)NbO₃-xSrTiO₃The lead-free piezoelectric ceramic (x is 0.02-0.10) has stable electrostrictive strain performance at high temperature and high compactness;

3. the ceramic material system can be prepared and synthesized by adopting a traditional solid-phase reaction method, and has the advantages of relatively simple process, easy operation and high repeatability.

Drawings

FIG. 1 is an XRD spectrum of a ST6 sample prepared in example 1, a ST0 sample prepared in comparative example 1, and a ST2 sample prepared in comparative example 2;

FIG. 2 is a plot of hysteresis loop and current for application of an electric field of 5kV/mm at room temperature for the ST6 sample prepared in example 1 of example 1, the ST0 sample prepared in comparative example 1, and the ST2 sample prepared in comparative example 2;

FIG. 3 is a graph showing uniaxial strain curves between 25 ℃ and 120 ℃ for the ST6 sample prepared in example 1, the ST0 sample prepared in comparative example 1, and the ST2 sample prepared in comparative example 2;

FIG. 4 shows the maximum electrostrictive (S) as a function of the test temperature for the ST6 sample obtained in example 1, the ST0 sample obtained in comparative example 1 and the ST2 sample obtained in comparative example 2;

FIG. 5 shows normalized strains (S) of ST6 sample prepared in example 1, ST0 sample prepared in comparative example 1, and ST2 sample prepared in comparative example 2_max/E_max) As a function of temperature.

Detailed Description

The present invention is further illustrated by the following examples, which are to be understood as merely illustrative and not restrictive. In the case where the present invention is not specifically described, "room temperature" means "about 25 ℃.

In order to solve the problem of poor strain temperature stability of the conventional lead-free piezoelectric ceramic material, the invention provides a lead-free piezoelectric ceramic materialThe lead-free piezoelectric ceramic material with high-temperature stable electrostriction has the chemical composition formula: (0.93-x) (Bi)_0.5Na_0.5)TiO₃-0.06BaTiO₃-0.01(K_0.5Na_0.5)NbO₃-xSrTiO₃Wherein x is 0.02-0.1. When x is less than 0.02, the strain-to-temperature change rate of the material from room temperature to 120 ℃ is 48-57%.

Preferably, x is 0.04 to 0.08. With the increase of x, the relative content of the relaxation phase in the material is gradually increased, so that the electric strain hysteresis degree of the material is gradually reduced, and the temperature stability is obviously enhanced. In some embodiments, the lead-free piezoceramic material has a strain change rate of less than 15% from room temperature to 120 ℃. Particularly, when x is 0.06, the obtained lead-free piezoelectric ceramic material can combine good electrostrictive property and relatively excellent temperature stability, the room temperature strain of the lead-free piezoelectric ceramic material reaches 0.20% under an electric field of 5kV/mm, the equivalent piezoelectric constant is about 400pm/V, and the strain-change temperature change rate is less than 15% between 25 ℃ and 120 ℃.

The invention is based on SrTiO₃Solid solution doping regulates the strain temperature stability of BNT-BT-KNN by utilizing a paraelectric SrTiO₃After entering into crystal lattice, the crystal lattice can break the action of ferroelectric long program of matrix, induce local relaxation structure in matrix and lower the ferroelectric-relaxation transition temperature of material to below room temperature, so as to lower the electric strain hysteresis degree of material and raise the strain temperature stability of material. It should be emphasized that although SrTiO₃Can also be used for the performance control of other perovskite materials, such as grain-refining, high insulation resistance xBNT-yBT-zST materials, but the invention focuses more on SrTiO₃The influence on the electrostriction and the temperature stability of the material is shown in the fact that the SrTiO obviously improves the temperature stability₃After lowering the ferroelectric-relaxed ferroelectric transition temperature of the material below room temperature.

The regulation mechanism has universality, and can also be applied to the design of other BNT-based ferroelectric materials such as BNT-BT-BKT and the like so as to realize the high-temperature stable electrostrictive property of the BNT-based ferroelectric materials.

The lead-free piezoelectric ceramic material with stable electrostriction at high temperature can be prepared and synthesized at lower temperature by adopting a traditional solid phase method. As an example, the present invention can be implemented by the following technical solutions:

with Bi₂O₃、Na₂CO₃、BaCO₃、K₂CO₃、Nb₂O₅、SrCO₃And TiO₂As a starting material, according to (0.93-x) (Bi)_0.5Na_0.5)TiO₃-0.06BaTiO₃-0.01(K_0.5Na_0.5)NbO₃-xSrTiO₃And weighing the raw materials according to the stoichiometric ratio of Bi, Na, Ba, K, Nb, Sr and Ti elements. And ball-milling and mixing the weighed raw materials to form mixed slurry. The solid content of the mixed slurry is 30-50%.

And drying and grinding the mixed slurry, and sieving to obtain mixed powder. Preferably, the mixed slurry is dried, ground and sieved by a 80-mesh sieve.

And preserving the heat of the mixed powder at 750-950 ℃ for 1-4 h for pre-sintering treatment. Preferably, the pre-sintering temperature is 800-900 ℃, and the pre-sintering heat preservation time is 2-3 h.

And performing secondary ball milling on the pre-sintered powder, drying and sieving to obtain (BNT-BT-KNN) -xST powder. And drying the powder subjected to secondary ball milling and then sieving the powder with a 200-mesh sieve.

And adding a binder into the synthesized (BNT-BT-KNN) -xST powder, granulating, sieving, and then performing compression molding to obtain a blank. In some embodiments, the binder is polyvinyl alcohol (PVA) with a concentration of 6%, and the amount of binder added is 10% of the mass of the (BNT-BT-KNN) -xST powder. The pressing molding can be performed under the pressure of 50-200 MPa.

And (3) preserving the heat of the blank at 450-650 ℃ for 0.5-3 h to perform plastic removal on the blank. Preferably, the plastic discharge temperature is 500-600 ℃; the plastic removal and heat preservation time is 1-2 h. For example, the plastic removal process parameters are as follows: heating to 500 ℃ from room temperature at the heating rate of 3 ℃/min, preserving heat for 2h, and then naturally cooling along with the furnace.

And heating the blank subjected to plastic removal to 1150-1200 ℃ at the speed of 2-5 ℃/min, preserving the heat for 2-5 h, and sintering to obtain the (BNT-BT-KNN) -xST lead-free piezoelectric ceramic material. The sintering temperature is preferably 1150-1180 ℃. The sintering heat preservation time is preferably 3-4 h. The sintering temperature rise rate is preferably 3-4 ℃/min.

In addition, before the piezoelectric performance test, silver and polarization treatment is also carried out on the lead-free piezoelectric ceramic material.

Is coated with silver. Grinding and polishing the lead-free piezoelectric ceramic material, coating silver paste on two surfaces, and sintering the silver electrode at the temperature of 550-650 ℃ for 20-40 min.

And (6) polarization. And (3) polarizing the silvered lead-free piezoelectric ceramic in a silicon oil bath. The polarization time is 30-60min, and the polarization electric field is 4-8 kV/mm.

The lead-free piezoelectric ceramic material prepared by the preparation method has high density and wide temperature stability. The invention has simple components and process steps, easy operation and good repeatability, can be applied to a driver with high requirement on temperature stability, and has great economic value.

The present invention is further described in the detailed description which follows in conjunction with the detailed description which is intended to be illustrative, but not limiting, of the invention, the scope of which is defined by the appended claims and their equivalents.

Example 1

A lead-free piezoelectric ceramic material having a high temperature stable electrostrictive, the ceramic material having a chemical composition of: 0.87 (Bi)_0.5Na_0.5)TiO₃-0.06BaTiO₃-0.01(K_0.5Na_0.5)NbO₃-0.06SrTiO₃ Abbreviated ST 6.

The preparation method of the ST6 ceramic comprises the following steps:

1) according to chemical formula 0.87 (Bi)_0.5Na_0.5)TiO₃-0.06BaTiO₃-0.01(K_0.5Na_0.5)NbO₃-0.06SrTiO₃In the weight ratio of Bi, Na, Ba, K, Nb, Sr and Ti, weighing Bi₂O₃、Na₂CO₃、BaCO₃、K₂CO₃、Nb₂O₅、SrCO₃And TiO₂Raw materials. Putting the weighed raw materials into a nylon ball milling tank with zirconia balls, and adding absolute ethyl alcoholSealing a ball milling tank, putting the ball milling tank into a ball mill for ball milling, filtering the mixed slurry, putting the filtered mixed slurry into an oven, drying the mixed slurry at 100 ℃, grinding the dried mixed slurry in a mortar, and sieving the ground mixed slurry with a 80-mesh sieve; then presintering the sieved powder in a high temperature furnace at 850 ℃, and preserving heat for 2 hours; then, secondary ball milling is carried out, and the slurry after ball milling is dried to obtain 0.87 (Bi)_0.5Na_0.5)TiO₃-0.06BaTiO₃-0.01(K_0.5Na_0.5)NbO₃-0.06SrTiO₃And (3) powder lot.

2) Grinding the powder dried in the step 1) in a mortar, sieving by a 200-mesh sieve, adding a polyvinyl alcohol (PVA) solution containing 6% for granulation, wherein the adding amount is about 10% of the mass of the powder, uniformly mixing, and sieving by a 40-mesh sieve to obtain a granule with good fluidity.

3) Putting a proper amount of the powder in the step 2) into a stainless steel mold, and pressing into a cylindrical blank under the pressure of 200 MPa.

4) Putting the blank in the step 3) into a high-temperature furnace, heating to 500 ℃ at the heating rate of 3 ℃/min, preserving heat for 2h for plastic removal, and then naturally cooling along with the furnace.

5) And (3) embedding the blank subjected to plastic removal in the step 4) into the same raw material powder, adding a crucible cover, putting the blank into a high-temperature furnace, heating to 1160 ℃ at the speed of 4 ℃/min, preserving heat for 3 hours, sintering, and naturally cooling along with the furnace to prepare the ceramic chip with good sintering.

6) Grinding and polishing the ceramic wafer sintered in the step 5), and then placing the ceramic wafer in absolute ethyl alcohol for ultrasonic cleaning and drying; and uniformly printing silver paste on the upper surface and the lower surface of the material by screen printing, then placing the material in a high-temperature furnace, heating to 600 ℃ at the speed of 3 ℃/min, preserving heat for 0.5h for silver burning, and then naturally cooling to room temperature to test the strain performance and the temperature stability of the material.

7) The electrical properties (hysteresis loop, current curve and strain curve) of the ST6 sample were tested under the following conditions: unpolarized samples were tested at a frequency of 1Hz with an applied electric field of 5kV/mm, and the test instrument was a ferroelectric test system equipped with a laser micrometer (TF2000E, aix-ACCT, Aachen, Germany). The XRD pattern test condition is that the sample is not polarized, and the surface of the sample is slightly polished.

Referring to fig. 1, the XRD pattern is that of the ST6 sample prepared in example 1. It can be seen that both characteristic peaks (111) and (200) are cleaved states, indicating the trigonal-tetragonal coexisting structure of ST6 sample site.

Referring to FIG. 2, the hysteresis loop and current curve at room temperature at 5kV/mm for the ST6 sample prepared in example 1. The hysteresis loop of the ST6 sample exhibited a lumbar contraction phenomenon, P_rAbout 5.5. mu.C/cm²,E_cAbout 0.60 kV/mm. The disappearance of the macro domain inversion current peak P1 in the current curve indicates that the ferroelectric phase corresponding to the macro domain has completely disappeared at room temperature. Meanwhile, a dispersed current peak P2 appears in the curve, which is a typical characteristic of the relaxed ferroelectric and corresponds to a polarity-reversal current peak of the polar nano-micro region, and since the polar nano-micro region is in a thermally activated state, a recovery current peak P2R corresponding to P2 can be observed when the applied electric field is removed. The complete disappearance of the P1 peak and the appearance of the P2 peak indicate that the ST6 sample at room temperature is a relaxed ferroelectric, and the ferroelectric-relaxation transition temperature thereof has been regulated to below room temperature, which is beneficial to the temperature stability of the electro-dependent strain performance of the material.

See the uniaxial strain curve between 25 ℃ and 120 ℃ for the ST6 sample in fig. 3. It can be seen that the strain hysteresis of the electrostrictive curve of this sample is between 11% and 42%, and the amount of electrostrictive strain (S) at 7 temperature test points_max) And the performance characteristics are more consistent.

See the S between 25 ℃ and 120 ℃ of the ST6 sample in FIG. 4_maxAs a function of the test temperature, it can be seen that the minimum strain of the sample is about 0.20% (25 ℃), the maximum strain is about 0.17% (120 ℃), and the rate of change is about 15%.

See the normalized strain (S) between 25 ℃ and 120 ℃ for the ST6 sample in FIG. 5_max/E_max) As a function of temperature. It can be seen that the normalized strain has a minimum value of 400pm/V and a maximum value of 320pm/V, with a rate of change of about 15%.

Example 2

Essentially the same as example 1, except that: the chemical composition of the ceramic material is 0.89 (Bi)_0.5Na_0.5)TiO₃-0.06BaTiO₃-0.01(K_0.5Na_0.5)NbO₃-0.04SrTiO₃。

Example 3

Essentially the same as example 1, except that: the chemical composition of the ceramic material is 0.85 (Bi)_0.5Na_0.5)TiO₃-0.06BaTiO₃-0.01(K_0.5Na_0.5)NbO₃-0.08SrTiO₃。

Comparative example 1

A lead-free piezoelectric ceramic material having a high temperature stable electrostrictive, the ceramic material having a chemical composition of: 0.93 (Bi)_0.5Na_0.5)TiO₃-0.06BaTiO₃-0.01(K_0.5Na_0.5)NbO₃ Abbreviated ST 0.

The preparation method of the ST0 ceramic comprises the following steps:

1) according to chemical formula 0.93 (Bi)_0.5Na_0.5)TiO₃-0.06BaTiO₃-0.01(K_0.5Na_0.5)NbO₃In the weight ratio of Bi, Na, Ba, K, Nb, Sr and Ti, weighing Bi₂O₃、Na₂CO₃、BaCO₃、K₂CO₃、Nb₂O₅、SrCO₃And TiO₂Raw materials. Putting the weighed raw materials into a nylon ball milling tank with zirconia balls, adding absolute ethyl alcohol as a ball milling medium, sealing the ball milling tank, putting the ball milling tank into a ball mill for ball milling, filtering the mixed slurry, putting the mixed slurry into an oven, drying the mixed slurry at 100 ℃, grinding the mixed slurry in a mortar, and sieving the ground slurry with a 80-mesh sieve; then presintering the sieved powder in a high temperature furnace at 850 ℃, and preserving heat for 2 hours; then, secondary ball milling is carried out, and the slurry after ball milling is dried to obtain 0.93 (Bi)_0.5Na_0.5)TiO₃-0.06BaTiO₃-0.01(K_0.5Na_0.5)NbO₃And (3) powder lot.

7) The electrical properties (hysteresis loop, current curve and strain curve) of the ST0 sample were tested under the following conditions: unpolarized samples were tested at a frequency of 1Hz with an applied electric field of 5kV/mm, and the test instrument was a ferroelectric test system equipped with a laser micrometer (TF2000E, aix-ACCT, Aachen, Germany). The XRD pattern test condition is that the sample is not polarized, and the surface of the sample is slightly polished.

Referring to fig. 1, the XRD pattern is that of the ST0 sample prepared in comparative example 1. It can be seen that both characteristic peaks (111) and (200) are cleaved states, indicating the trigonal-tetragonal coexisting structure of ST0 sample site.

Referring to FIG. 2, the hysteresis loop and current curve at room temperature at 5kV/mm for the ST0 sample prepared in comparative example 1. The hysteresis loop of the ST0 sample is a square hysteresis loop of a typical ferroelectric, and has a larger P_rAnd E_cOnly the ferroelectric macro domain switching current peak P1 appears in the current curve.

See the uniaxial strain curve between 25 ℃ and 120 ℃ for the ST0 sample in fig. 3. It can be seen that the hysteresis of the electrostrictive strain curve of this sample reaches 65% and at 7 temperaturesAmount of electrostrictive strain (S) of degree test point_max) It shows a first-increasing and then-decreasing characteristic because the ferroelectric-relaxation transition temperature of the ST0 sample is around 65 ℃, and domain inversion is relatively easy at the phase transition temperature, so that large electric strain is obtained, but the temperature stability of the electric strain performance of the STO sample is adversely affected.

See the S between 25 ℃ and 120 ℃ of the ST0 sample in FIG. 4_maxAs a function of the test temperature, it can be seen that the minimum strain of the sample is about 0.14% (25 ℃), the maximum strain is about 0.32% (65 ℃) and the rate of change is about 57%.

See the normalized strain (S) between 25 ℃ and 120 ℃ for the ST0 sample in FIG. 5_max/E_max) As a function of temperature. It can be seen that the normalized strain has a minimum value of 280pm/V and a maximum value of 640pm/V, with a rate of change of about 57%.

Comparative example 2

A lead-free piezoelectric ceramic material having a high temperature stable electrostrictive, the ceramic material having a chemical composition of: 0.91 (Bi)_0.5Na_0.5)TiO₃-0.06BaTiO₃-0.01(K_0.5Na_0.5)NbO₃-0.02SrTiO₃ Abbreviated ST 2.

The preparation method of the ST2 ceramic comprises the following steps:

1) according to chemical formula 0.91 (Bi)_0.5Na_0.5)TiO₃-0.06BaTiO₃-0.01(K_0.5Na_0.5)NbO₃-0.02SrTiO₃In the weight ratio of Bi, Na, Ba, K, Nb, Sr and Ti, weighing Bi₂O₃、Na₂CO₃、BaCO₃、K₂CO₃、Nb₂O₅、SrCO₃And TiO₂Raw materials. Putting the weighed raw materials into a nylon ball milling tank with zirconia balls, adding absolute ethyl alcohol as a ball milling medium, sealing the ball milling tank, putting the ball milling tank into a ball mill for ball milling, filtering the mixed slurry, putting the mixed slurry into an oven, drying the mixed slurry at 100 ℃, grinding the mixed slurry in a mortar, and sieving the ground slurry with a 80-mesh sieve; then presintering the sieved powder in a high temperature furnace at 850 ℃, and preserving heat for 2 hours; then carrying out a second timeBall milling, and drying the ball milled slurry to obtain 0.91 (Bi)_0.5Na_0.5)TiO₃-0.06BaTiO₃-0.01(K_0.5Na_0.5)NbO₃-0.02SrTiO₃And (3) powder lot.

7) The electrical properties (hysteresis loop, current curve and strain curve) of the ST2 sample were tested under the following conditions: unpolarized samples were tested at a frequency of 1Hz with an applied electric field of 5kV/mm, and the test instrument was a ferroelectric test system equipped with a laser micrometer (TF2000E, aix-ACCT, Aachen, Germany). The XRD pattern test condition is that the sample is not polarized, and the surface of the sample is slightly polished.

Referring to fig. 1, the XRD pattern is that of the ST2 sample prepared for the comparative example 2. It can be seen that both characteristic peaks (111) and (200) are cleaved states, indicating the trigonal-tetragonal coexisting structure of ST2 sample site.

Referring to FIG. 2, areThe ST2 sample prepared in comparative example 2 has a hysteresis loop and a current curve at room temperature and 5 kV/mm. Similar to the ST6 sample of example I, the hysteresis loop of the ST2 sample also exhibited lumbar contraction, P_rAbout 7.8. mu.C/cm²,E_cAbout 0.95 kV/mm. However, the macro domain inversion current peak P1 in the current curve of the ST2 sample did not disappear, and the simultaneous appearance of the P1 peak and the P2 peak indicates that the ST2 sample is in a ferroelectric-relaxor ferroelectric coexisting state at room temperature. It should be noted that the macro-domain inversion current peak P2 of the ST2 sample was shifted toward the high electric field direction and had a tendency to be weakened, compared to the ST0 sample prepared in comparative example 1, indicating that macro-domain inversion became difficult with the introduction of ST and its contribution to performance was also weakened.

See the uniaxial strain curve between 25 ℃ and 120 ℃ for the ST2 sample in fig. 3. It can be seen that the sample has the electrostrictive strain (S) at 7 temperature test points_max) Shows a linear descending trend, which is that the ferroelectric-relaxation transition temperature of the macro domain corresponding to the ferroelectric phase in the material is adjusted to be near the room temperature, and the strain quantity is gradually reduced as the testing temperature deviates from the phase transition point.

See the S between 25 ℃ and 120 ℃ of the ST2 sample in FIG. 4_maxAs a function of the test temperature, it can be seen that the minimum strain of the sample is about 0.29% (25 ℃), the maximum strain is about 0.15% (120 ℃), and the rate of change is about 48%. The larger temperature change rate is because the ferroelectric-relaxation transition temperature of the ferroelectric phase corresponding to the macro domain is closer to the test temperature range, and the influence of the ferroelectric-relaxation transition temperature on the stability of the temperature change is still obvious.

See the normalized strain (S) between 25 ℃ and 120 ℃ for the ST2 sample in FIG. 5_max/E_max) As a function of temperature. It can be seen that the normalized strain has a minimum value of 580pm/V and a maximum value of 300pm/V, with a rate of change of about 48%. Similarly, a greater rate of temperature change is associated with a ferroelectric-to-relaxation transition temperature of the corresponding ferroelectric phase of the macro-domain being closer to the test temperature interval.

Claims

1. A lead-free piezoceramic material with high-temperature stable electrostriction, characterized in that the material is a lead-free piezoceramic materialHas the chemical general formula: (0.93-x)(Bi_0.5Na_0.5)TiO₃-0.06BaTiO₃-0.01(K_0.5Na_0.5)NbO₃-xSrTiO₃Whereinx=0.02~0.1。

2. The lead-free piezoelectric ceramic material according to claim 1,x=0.04~0.08。

3. the lead-free piezoelectric ceramic material of claim 1 or 2, wherein the strain hysteresis of the lead-free piezoelectric ceramic material is from 11% to 42%; the lead-free piezoelectric ceramic material has strain response characteristics close to linear dielectric at 25-120 ℃.

4. The lead-free piezoelectric ceramic material according to any one of claims 1 to 3, wherein the lead-free piezoelectric ceramic material has a temperature rate of change of maximum electrostriction and normalized strain within 15% at 25 to 120 ℃.

5. The method for preparing a lead-free piezoceramic material with high temperature stable electrostriction according to any one of claims 1 to 4, characterized by comprising the steps of:

1) according to (0.93-x)(Bi_0.5Na_0.5)TiO₃-0.06BaTiO₃-0.01(K_0.5Na_0.5)NbO₃-xSrTiO₃In the stoichiometric ratio of Bi, Na, Ba, K, Nb, Sr and Ti elements, each raw material Bi is weighed₂O₃、Na₂CO₃、BaCO₃、K₂CO₃、Nb₂O₅、SrCO₃And TiO₂Uniformly mixing the raw materials to form mixed slurry; drying, grinding and sieving the mixed slurry to obtain mixed powder;

2) pre-sintering the mixed powder at 750-950 ℃ for 1-4 h, cooling to room temperature along with the furnace, performing secondary ball milling, drying, grinding and sieving to obtain (BNT-BT-KNN)xST powder;

3) the (BNT-BT-KNN) prepared in the step 2)xPressing and molding ST powder to form a blank;

6. The preparation method according to claim 5, wherein in the step 2), the pre-sintering temperature is 800-900 ℃, and the pre-sintering heat preservation time is 2-3 h.

7. The method as claimed in claim 5 or 6, wherein in step 2), (BNT-BT-KNN) -xThe particle size of ST powder is 0.05-2.0 μm.

8. The method as claimed in any one of claims 5 to 7, wherein in step 3) (BNT-BT-KNN) before press formingxAdding a binder into the ST powder, granulating and sieving; preferably, the adhesive is polyvinyl alcohol with the mass fraction of 4-8%, and the addition amount of the adhesive is (BNT-BT-KNN) -x5-10% of ST powder mass.

9. The preparation method according to any one of claims 5 to 8, wherein in the step 4), the blank is subjected to heat preservation at 450-650 ℃ for 0.5-3 h before sintering so as to perform plastic removal on the blank.

10. The method as claimed in any one of claims 5 to 9, wherein the sintering temperature in step 4) is 1150-1180 ℃ and the sintering temperature is 3-4 h.