阅读说明：本技术 一种高稳定的无铅压电陶瓷及其制备方法 (High-stability lead-free piezoelectric ceramic and preparation method thereof ) 是由 姜知水 文理 董进杰 于 2021-07-13 设计创作，主要内容包括：本发明涉及一种高稳定的无铅压电陶瓷,所述无铅压电陶瓷的化学式如下：(1-x-y)(0.50KNbO-(3)-0.50NaNbO-(3))-xMgTiO-(3)-yBa(Zr-(0.5)Ti-(0.5))O-(3)+zSm-(2)O-(3)；其中,x＝0.03～0.07,y＝0.04～0.08,z＝0.008～0.02。该无铅压电陶瓷采用一种工艺简单、高效率、低能耗、成本低廉且很具实用性的无铅压电陶瓷的制备方法,制得的KNN-MT-BZT无铅压电陶瓷烧后的晶粒为菱形,而且晶粒平均晶粒为3微米,取代之前的KNN体系的烧后的四方形晶粒,密度更高,性质稳定、致密、性能良好。(The invention relates to a high-stability lead-free piezoelectric ceramic, which has the following chemical formula: (1-x-y) (0.50KNbO 3 ‑0.50NaNbO 3 )‑xMgTiO 3 ‑yBa(Zr 0.5 Ti 0.5 )O 3 +zSm 2 O 3 (ii) a Wherein x is 0.03-0.07, y is 0.04-0.08, and z is 0.008-0.02. The lead-free pressThe electric ceramic adopts a preparation method of the leadless piezoelectric ceramic with simple process, high efficiency, low energy consumption, low cost and high practicability, the sintered crystal grains of the prepared KNN-MT-BZT leadless piezoelectric ceramic are rhombic, the average crystal grain size of the crystal grains is 3 micrometers, and the sintered tetragonal crystal grains of the previous KNN system are replaced, so that the density is higher, the property is stable and compact, and the performance is good.)

1. A high-stability lead-free piezoelectric ceramic is characterized in that crystal grains of the lead-free piezoelectric ceramic after being fired are rhombic, and the chemical formula of the lead-free piezoelectric ceramic is as follows:

(1-x-y)(0.50KNbO₃-0.50NaNbO₃)-xMgTiO₃-yBa(Zr_0.5Ti_0.5)O₃+zSm₂O₃(ii) a Wherein x is 0.03-0.07, y is 0.04-0.08, and z is 0.008-0.02.

2. The highly stable lead-free piezoelectric ceramic according to claim 1, wherein the chemical formula of the lead-free piezoelectric ceramic is as follows:

(1-x-y)(0.50KNbO₃-0.50NaNbO₃)-xMgTiO₃-yBa(Zr_0.5Ti_0.5)O₃+zSm₂O₃(ii) a Wherein x is 0.05, y is 0.06 and z is 0.015.

3. A method for producing a highly stable lead-free piezoelectric ceramic as claimed in claim 1 or 2, comprising the steps of:

s01, batching: first, the raw material Na is calculated and weighed in accordance with the composition of the highly stable lead-free piezoelectric ceramic as claimed in claim 1 or 2₂CO₃、K₂CO₃、Nb₂O₅、TiO₂，MgO，Ba CO，ZrO₂And Sm₂O₃Then, the raw materials are mixed in a ball mill tank to obtain mixed powder;

s02 Synthesis: drying the mixed powder obtained in the step S01, and performing synthetic reaction for 2.5 hours at 800-950 ℃ in an alumina crucible under a sealed condition to obtain a synthetic material;

s03 molding and plastic removal: firstly, ball-milling and mixing the synthesized material obtained in the step S02, drying the mixture, casting the mixture into a film, punching the film into a blank, heating the blank to 400 ℃ in two sections, preserving the temperature for 60min, heating the blank to 650 ℃ at the speed of 5 ℃/min, preserving the temperature for 120min, and discharging organic matters;

s04 sintering: burying and burning the green body obtained in the step S03 after the organic matters are discharged by using the partial material obtained in the step S02: heating to 1230 ℃ at the speed of 3 ℃/min, preserving heat for 2 hours, and cooling along with the furnace to obtain a sintered green body;

s05 coating silver electrode, firing silver: ultrasonically washing and drying the sintered blank obtained in the step S04, then coating silver on the sintered blank, putting the silver into a heating furnace, heating to 800 ℃, preserving the temperature for 10min, and naturally cooling to room temperature to obtain a silver-fired product;

s06 polarization: and (4) applying a direct current electric field of 1500V/mm to the silver-fired product obtained in the step (S05) in air at 100 ℃, and polarizing for 10min to obtain the high-stability lead-free piezoelectric ceramic.

4. The method of claim 3, wherein the conditions for ball milling and mixing in steps S01 and S03 are: the ball milling medium is deionized water and ZrO₂The rotating speed of the ball milling tank is 750r/min, and the ball milling time is 2.5 h.

5. The method of claim 4, wherein the ratio of raw materials/materials: ZrO (ZrO)₂Ball: the weight ratio of the deionized water is 1: 2.5: 1.

6. the method of claim 3, wherein the drying in steps S02, S03 and S05 is drying in a drying oven at 60-100 ℃.

7. The method according to claim 3, wherein in step S03: the weight ratio of the casting water agent is 100: 1.

8. The method according to claim 3, wherein the billet in step S03 has a diameter of 17.20mm and a thickness of 12.5 ± 0.5 um.

9. The method according to claim 3, wherein the two-stage temperature increase in step S03 is: the blank is first heated to 200 deg.c at a rate of 3 deg.c/min and then heated from 200 deg.c to 400 deg.c at a rate of 2 deg.c/min.

10. The method for preparing the silver paste of claim 3, wherein the silver paste of step S05 is prepared by a screen printing process.

Technical Field

The invention relates to the technical field of lead-free piezoelectric ceramics with perovskite structures, in particular to high-stability lead-free piezoelectric ceramics and a preparation method thereof.

Background

Piezoelectric ceramics and piezoelectric ceramic devices have been widely used in industries, particularly in the information industry field. With lead zirconate titanate (Pb (Ti, Zr) O₃) Lead-based binary system represented by the following and lead zirconate titanate (Pb (Ti, Zr) O)₃) Based on the addition of a third component, e.g. lead magnesium niobate (Pb (Mg1/3 Nb)_2/3)O₃) Antimony manganese acid lead Pb (Mn)_1/3Sb_2/3)O₃The lead-based ternary piezoelectric ceramic has excellent piezoelectric ferroelectric property and high Curie temperature. The majority of piezoelectric ceramics applied in industrial production are perovskite lead-based piezoelectric ceramics.

However, in the lead-based piezoelectric ceramics, PbO or Pb₃O₄The content of (A) is about 65% of the total mass of the raw materials. Lead pollution has become one of the human public hazards. Lead-based piezoelectric ceramics cause serious harm to human and ecological environment in the processes of production, use and waste post-treatment, and are not beneficial to sustainable development of human society. In recent years, the development of lead-free piezoelectric ceramic systems with excellent performance has been receiving increasing attention from countries of the world, particularly europe, america, japan, korea, and china.

There are four types of lead-free piezoelectric ceramic systems that are widely studied at present: bismuth-layered lead-free piezoelectric ceramic and BaTiO₃Base lead-free piezoelectric ceramic, Bi_0.5Na_0.5TiO₃Base lead-free piezoelectric ceramic and K_0.5Na_0.5NbO₃Alkali metal niobate is a lead-free piezoelectric ceramic. Among them, the KNN-based lead-free piezoelectric ceramic is one of the most possible systems for replacing lead-based piezoelectric ceramic at present due to its characteristics of small dielectric constant, high piezoelectric performance, large frequency constant, small density, high curie temperature, etc. However, the conventional process for obtaining KNN piezoelectric ceramics has the following disadvantages: (1) above 1140 ℃, a liquid phase of KNN occurs, so the temperature stability of KNN is limited to below 1140 ℃. (2) As Na and K will be oxidized into Na at 900 deg.C₂O and K₂The formation of O begins to volatilize, causingThe atmosphere of firing and sintering is difficult to control; (3) KNN is very easy to deliquesce in a humid environment, so that stoichiometry deviates, a heterogeneous phase is generated, and the ceramic is difficult to sinter and compact. The practical application of the KNN system material is limited by the reasons.

In order to optimize the structure of the KNN-based lead-free piezoelectric ceramic and improve the piezoelectric performance of the KNN-based piezoelectric ceramic, various scholars perform a great deal of research on the KNN-based lead-free piezoelectric ceramic from the aspects of adding sintering aids, doping substitution of A site and B site, adding new components and the like; meanwhile, the process methods such as hot pressing, discharge plasma, hot isostatic pressing sintering and the like are combined to obtain compact KNN ceramics; however, the above-mentioned preparation method has high requirements for equipment, harsh production process, high production cost, limited material size, and unsatisfactory stability of the prepared ceramic, and thus it is difficult to achieve industrial application.

Disclosure of Invention

In order to overcome the above technical problems of the prior art, a first object of the present invention is to provide a highly stable lead-free piezoelectric ceramic having the following chemical formula: (1-x-y) (0.50KNbO₃-0.50NaNbO₃)-xMgTiO₃-yBa(Zr_0.5Ti_0.5)O₃+zSm₂O₃(ii) a Wherein x is 0.03-0.07, y is 0.04-0.08, and z is 0.008-0.02.

Preferably, the chemical formula of the lead-free piezoelectric ceramic is as follows: (1-x-y) (0.50KNbO₃-0.50NaNbO₃)-xMgTiO₃-yBa(Zr_0.5Ti_0.5)O₃+zSm₂O₃(ii) a Wherein x is 0.05, y is 0.06 and z is 0.015. The lead-free piezoelectric ceramic prepared at the synthesis reaction temperature of 850 ℃ and the firing temperature of 1230 ℃ has the best comprehensive piezoelectric performance, wherein epsilon_r2300, tan delta 0.013, k_p46.8% of d₃₃392pC/N, a higher Curie temperature Tc of 315 ℃ and a density p of 4.339g/cm³。

The second object of the present invention is to provide a method for preparing the above highly stable lead-free piezoelectric ceramic, which comprises the following steps:

s01, batching: first, the raw material Na is calculated and weighed according to the composition of the highly stable lead-free piezoelectric ceramic₂CO₃、K₂CO₃、Nb₂O₅、TiO₂，MgO，BaCO，ZrO₂And Sm₂O₃Then, the raw materials are mixed in a ball mill tank to obtain mixed powder;

s02 Synthesis: drying the mixed powder obtained in the step S01, and performing synthetic reaction for 2.5 hours at 800-950 ℃ in an alumina crucible under a sealed condition to obtain a synthetic material;

s03 molding and plastic removal: firstly, ball-milling and mixing the synthesized material obtained in the step S02, drying the mixture, casting the mixture into a film, punching the film into a blank, heating the blank to 400 ℃ in two sections, preserving the temperature for 60min, heating the blank to 650 ℃ at the speed of 5 ℃/min, preserving the temperature for 120min, and discharging organic matters; wherein, the material: the weight ratio of the casting water agent is 100: 1. The diameter of the blank is 17.20mm, and the thickness is 12.5 +/-0.5 um. The two-stage heating comprises the following steps: the blank is first heated to 200 deg.c at a rate of 3 deg.c/min and then heated from 200 deg.c to 400 deg.c at a rate of 2 deg.c/min.

S04 sintering: burying and burning the green body obtained in the step S03 after the organic matters are discharged by using the partial material obtained in the step S02: heating to 1230 ℃ at the speed of 3 ℃/min, preserving heat for 2 hours, and cooling along with the furnace to obtain a sintered green body;

s05 coating silver electrode, firing silver: ultrasonically washing and drying the sintered blank obtained in the step S04, then coating silver on the sintered blank, putting the silver into a heating furnace, heating to 800 ℃, preserving the temperature for 10min, and naturally cooling to room temperature to obtain a silver-fired product; wherein, the silver adopts a screen printing process.

S06 polarization: and (4) applying a direct current electric field of 1500V/mm to the silver-fired product obtained in the step (S05) in air at 100 ℃, and polarizing for 10min to obtain the high-stability lead-free piezoelectric ceramic.

Further, the conditions of the ball milling mixing in steps S01 and S03 are: the ball milling medium is deionized water and ZrO₂The rotating speed of the ball milling tank is 750r/min, and the ball milling time is 2.5 h. And raw materials/materials: ZrO (ZrO)₂Ball: deionizationThe weight ratio of water is 1: 2.5: 1.

further, the drying in steps S02, S03 and S05 is drying in a drying oven at 60-100 ℃.

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

(1) at 1140 degrees, the conventional KNN system volatilizes much Na2O and K2O, so that the density and the performance of the product are low, and the product cannot be commercially applied in a large scale. The invention adds xMgTiO₃-yBa(Zr_0.5Ti_0.5)O₃+zSm₂O₃These substances prevent volatilization of Na2O and K2O sintered at 1230 deg.C, form a dense ceramic body, and improve the density and electrical properties of the product.

(2) The prior art can use hot pressing, spark plasma, hot isostatic pressing sintering and other technological methods to obtain high-density KNN ceramics, but sintering equipment is expensive, a protective atmosphere and a high-precision die are required to be added, the cost is higher than 1230 degrees of the common air sintering of the method, and the cost is many times (at least 5 times) higher than that of the method without pressurization.

(3) Compared with pure KNN lead-free piezoelectric ceramics, the lead-free piezoelectric ceramics of the invention has the advantages of obvious piezoelectric and ferroelectric properties, higher Curie temperature, optimal piezoelectric thermal stability and the like, the piezoelectric properties of the lead-free piezoelectric ceramics are obviously improved, the lead-free piezoelectric ceramics can be used for electronic devices such as piezoelectric surface-mounted buzzers, piezoelectric ceramic drivers and the like, the higher requirements of the electronic devices on the piezoelectric properties of the lead-free piezoelectric ceramics can be met, and the lead-free piezoelectric ceramics have bright market prospects and development potentials.

(4) The preparation method of the lead-free piezoelectric ceramic is simple in process, high in efficiency, low in energy consumption, low in cost and very practical, and the sintered crystal grains of the prepared KNN-MT-BZT lead-free piezoelectric ceramic are rhombic, the average crystal grain size of the crystal grains is 3 microns, the sintered tetragonal crystal grains of the previous KNN system are replaced, the density is higher, moisture absorption is difficult, the property is stable and compact, and the performance is good.

Drawings

FIG. 1 shows the dielectric constant ε^T ₃₃/ε₀In whichThe X axis is (1-X-y) (0.50KNbO₃-0.50NaNbO₃)-xMgTiO₃-yBa(Zr_0.5Ti_0.5)O₃+zSm₂O₃The substitution quantity X and Y axis of the medium MgTiO3 are dielectric constants epsilon^T ₃₃/ε₀The value is obtained.

FIG. 2 shows the piezoelectric coefficient d₃₃Wherein the X-axis is (1-X-y) (0.50 KNbO)₃-0.50NaNbO₃)-xMgTiO₃-yBa(Zr_0.5Ti_0.5)O₃+zSm₂O₃Substitution Y of meso-yBa (Zr0.5Ti0.5) O3, Y-axis being piezoelectric coefficient d₃₃The unit is pC/N.

FIG. 3 is a graph showing a variation of the electromechanical coupling coefficient KP, wherein the X-axis is (1-X-y) (0.50 KNbO)₃-0.50NaNbO₃)-xMgTiO₃-yBa(Zr_0.5Ti_0.5)O₃+zSm₂O₃The substitution quantity Z and Y axis of the Sm2O3 are electromechanical coupling coefficients K_PIn percent.

FIG. 4 shows (1-x-y) (0.50KNbO₃-0.50NaNbO₃)-xMgTiO₃-yBa(Zr_0.5Ti_0.5)O₃+zSm₂O₃The product of (2) is a fired grain.

Detailed Description

The present invention will now be described in more detail with reference to the following examples, but it should be understood that the invention is not limited to the details of the examples set forth herein. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Examples and comparative examples

In the examples of the present invention and the comparative examples, the raw materials used were all commercially available products in which Na was contained₂CO₃、K₂CO₃、Nb₂O₅、TiO₂，MgO，BaCO，ZrO₂And Sm₂O₃All are chemically pure. The piezoelectric ceramics provided in the specific examples of the present invention and the comparative examples were prepared in the following manner, except that (Ba)_XMg_YW_Z) The substitution amount and the synthesis reaction temperature.

A preparation method of high-stability lead-free piezoelectric ceramics comprises the following steps:

s01, batching: firstly, according to the chemical formula of the lead-free piezoelectric ceramic with high stability [ 1-x-y ] (0.50 KNbO)₃-0.50NaNbO₃)-xMgTiO₃-yBa(Zr_0.5Ti_0.5)O₃+zSm₂O₃(ii) a Wherein, the components of x is 0.03-0.07, y is 0.04-0.08, and z is 0.008-0.02 are calculated and called as raw material Na₂CO₃、K₂CO₃、Nb₂O₅、TiO₂，MgO，BaCO，ZrO₂And Sm₂O₃Then, the raw materials are mixed in a ball mill tank to obtain mixed powder; wherein, the ball milling medium is deionized water and ZrO₂Ball, raw materials: ZrO (ZrO)₂Ball: the weight ratio of the deionized water is 1: 2.5: 1, the rotating speed of the ball milling tank is 750r/min, and the ball milling time is 2.5 h.

S02 Synthesis: drying the mixed powder obtained in the step S01 in a drying oven at 60-100 ℃, then putting the dried mixed powder into an alumina crucible, covering and sealing the alumina crucible, and carrying out synthetic reaction for 2.5 hours at 800-950 ℃ to obtain synthetic (1-x-y) (0.50 KNbO)₃-0.50NaNbO₃)-xMgTiO₃-yBa(Zr_0.5Ti_0.5)O₃+zSm₂O₃Material preparation;

s03 molding and plastic removal: first, the synthesized (1-x-y) (0.50 KNbO) obtained in step S02 is used₃-0.50NaNbO₃)-xMgTiO₃-yBa(Zr_0.5Ti_0.5)O₃+zSm₂O₃Ball-milling and mixing materials (wherein the ball-milling medium is deionized water and ZrO2 balls, the weight ratio of the materials to the ZrO2 balls to the deionized water is 1: 2.5: 1, the rotation speed of a ball-milling tank is 750r/min, the ball-milling time is 2.5h), drying in a drying box at the temperature of 60-100 ℃, and drying according to (1-x-y) (0.50 KNbO)₃-0.50NaNbO₃)-xMgTiO₃-yBa(Zr_0.5Ti_0.5)O₃+zSm₂O₃Materials: (1-x-y) (0.50 KNbO) dried in the weight ratio of casting water agent of 100:1₃-0.50NaNbO₃)-xMgTiO₃-yBa(Zr_0.5Ti_0.5)O₃+zSm₂O₃Adding the material into the existing casting water agent, uniformly stirring, casting into a membrane with the thickness of 1-50um in an automatic casting machine, and punching into a blank with the diameter of 17.20mm and the thickness of 12.5 +/-0.5 um; and then heating the blank body to 200 ℃ at the speed of 3 ℃/min, heating the blank body to 400 ℃ from 200 ℃ at the speed of 2 ℃/min, preserving the heat at 400 ℃ for 60min, and heating the blank body to 650 ℃ at the speed of 5 ℃/min, preserving the heat for 120min, so as to discharge organic matters.

S04 sintering: the organic matter-discharged green body obtained in step S03 was treated with the fraction (1-x-y) (0.50 KNbO) obtained in step S02 in a closed vessel₃-0.50NaNbO₃)-xMgTiO₃-yBa(Zr_0.5Ti_0.5)O₃+zSm₂O₃Burying and burning materials: so as to avoid the change of the components in the product caused by the volatilization of KNa in the sintering process of the green body. The sintering conditions are as follows: heating to 1230 ℃ at the speed of 3 ℃/min, preserving heat for 2 hours, and cooling along with the furnace to obtain a sintered green body;

s05 coating silver electrode, firing silver: and (4) ultrasonically washing the sintered blank obtained in the step (S04) for 30min at normal temperature and at the frequency of 20-100khz, drying in a drying oven at the temperature of 60-100 ℃, coating silver by adopting a screen printing process, placing in a heating furnace, heating to 800 ℃, preserving heat for 10min, and naturally cooling to room temperature to obtain a silver-fired product.

S06 polarization: and (4) applying a direct current electric field of 1500V/mm to the silver-fired product obtained in the step (S05) in air at 100 ℃ in a polarization box, and polarizing for 10min to obtain the high-stability lead-free piezoelectric ceramic.

TABLE 1 (1-x-y) (0.50 KNbO) in examples and comparative examples₃-0.50NaNbO₃)-xMgTiO₃-yBa(Zr_0.5Ti_0.5)O₃+zSm₂O₃Substitution amount and synthesis reaction temperature of

	Formulation ratio	Calcination temperature C
			Comparative example 1	X＝0.00，Y＝0.00，Z＝0.00	900
Examples 1 to 1	X＝0.03，Y＝0.00，Z＝0.00	800
			Examples 1 to 2	X＝0.05，Y＝0.00，Z＝0.00	850
Examples 1 to 3	X＝0.07，Y＝0.00，Z＝0.00	900
			Comparative example 2	X＝0.05，Y＝0.00，Z＝0.00	850
Example 2-1	X＝0.05，Y＝0.04，Z＝0.00	850
			Examples 2 to 2	X＝0.05，Y＝0.06，Z＝0.00	850
Examples 2 to 3	X＝0.05，Y＝0.08，Z＝0.00	850
			Comparative example 3	X＝0.05，Y＝0.06，Z＝0.00	850
Example 3-1	X＝0.05，Y＝0.06，Z＝0.008	850
			Examples 3 to 2	X＝0.05，Y＝0.06，Z＝0.015	850
Examples 3 to 3	X＝0.05，Y＝0.06，Z＝0.02	850

Test method

After the piezoelectric ceramics provided by the embodiments and the comparative examples of the present invention were left at room temperature for 24 hours, the piezoelectric performance parameters of the piezoelectric ceramics were tested for loss value tan δ and dielectric constant ε^T ₃₃/ε₀Piezoelectric coefficient d₃₃And electromechanical coupling coefficient K_PThe density is measured by the following specific test method:

1. loss value tan delta and dielectric constant epsilon^T ₃₃/ε₀The test method (2): the 4225 LCR automatic measuring instrument produced by six radio factories in Tianjin, China can be used for measuring the loss value tan delta of the piezoelectric ceramic sample at room temperature, and the measuring frequency is 1 Kz; under the same conditions as described above, the capacitance was measured, and the dielectric constant ε was calculated by the following equation^T ₃₃/ε₀：

In the formula (I), the compound is shown in the specification,

c-the capacitance, F,

t-thickness of the piezoelectric ceramic sample, cm,

phi-diameter of the circular silver electrode of the piezoelectric ceramic sample, cm,

ε₀vacuum dielectric constant, F/m.

2. Piezoelectric coefficient d₃₃The test method (2): the piezoelectric coefficient d can be tested by adopting a ZJ-3A type quasi-static tester provided by the acoustics of Chinese academy of sciences according to the method specified in the national standard GB11309-89₃₃The unit is pC/N.

3. Electromechanical coupling coefficient K_PThe test method (2): measuring and calculating by adopting a resonance-anti-resonance method to obtain the electromechanical coupling coefficient K_PThe specific method is to measure the resonant frequency f of the piezoelectric vibrator by an HP4294A precision impedance analyzer_rAnd anti-resonant frequency f_aCalculating the electromechanical coupling coefficient K according to the following formula_P：

In the formula:

f_r-the resonance frequency of the resonant frequency,

f_a-an anti-resonance frequency.

4. Density of samples three samples were calculated for each component by measuring diameter, thickness and mass and averaging. And acquiring ceramic ray diffraction data by adopting an advanced diffraction measurement system.

The piezoelectric properties of the piezoelectric ceramics provided in the examples and comparative examples of the present invention were measured by the above-described methods, and the loss values tan δ and the dielectric constants ε were obtained^T ₃₃/ε₀Piezoelectric coefficient d₃₃And electromechanical coupling coefficient K_PThe values and densities are shown in Table 2.

	εT 33/ε0	d33(pC/N)	KP(％)	tanδ(％)	ρ
						Comparative example 1	1200	120	19	3.0	4.01
Examples 1 to 1	1300	120	28	1.7	4.0
						Examples 1 to 2	1600	170	30	1.6	4.05
Examples 1 to 3	1400	150	26	1.2	4.08
						Comparative example 2	1900	262	36.8	1.8	4.039
Example 2-1	2000	272	35.8	2.5	4.139
						Examples 2 to 2	2100	332	41.3	1.8	4.19
Examples 2 to 3	2050	312	37.8	2.2	4.16
						Comparative example 3	2050	330	42.3	1.5	4.221
Example 3-1	2100	332	41.8	1.8	4.239
						Examples 3 to 2	2300	392	46.8	1.3	4.339
Examples 3 to 3	2100	360	42.3	1.5	4.221

As can be seen by combining table 1 and table 2: when X is 0.05, Y is 0.06, Z is 0.015, and the synthesis reaction temperature is 850 ℃, the firing temperature is 1230 ℃, the obtained modified piezoelectric ceramic has the best overall piezoelectric performance, wherein epsilon r is 2300, tan delta is 0.013, Kp is 46.8%, d33 is 392pC/N, the density rho is 4.339g/cm3, and the higher curie temperature Tc is 315 ℃.

As can be seen from FIG. 1, the dielectric constant ε of MgTiO3 complex-substituted modified piezoelectric ceramic is shown in comparison with pure KNN piezoelectric ceramic^T ₃₃/ε₀Is improved. (1-x-y) (0.50 KNbO) at different synthesis temperatures₃-0.50NaNbO₃)-xMgTiO₃-yBa(Zr_0.5Ti_0.5)O₃+zSm₂O₃Increase in the amount of substitution X of medium Ba, and dielectric constant ε^T ₃₃/ε₀Shows an increasing tendency, and when the substitution amount X is 0.05, the dielectric constant ε^T ₃₃/ε₀Reaches a maximum value and has a dielectric constant ε at a synthesis temperature of 850 DEG C^T ₃₃/ε₀A maximum value of 1600 is reached.

As can be seen from FIG. 2, yBa (Zr)_0.5Ti_0.5)O₃Piezoelectric coefficient d of composite substituted and modified piezoelectric ceramic₃₃Is improved.

Sm can be seen in FIG. 3₂O₃Electromechanical coupling coefficient K of added modified piezoelectric ceramic_PIs improved. With (1-x-y) (0.50KNbO₃-0.50NaNbO₃)-xMgTiO₃-yBa(Zr_0.5Ti_0.5)O₃+zSm₂O₃Middle Sm₂O₃Increase of the substitution Z, coefficient of electromechanical coupling K_PShows an increasing trend, when the substitution quantity X is 0.015, the electromechanical coupling coefficient K_PReaches a maximum value, K increases with the amount added_PAnd then decreases again.

As can be seen from FIG. 4, (1-x-y) (0.50 KNbO)₃-0.50NaNbO₃)-xMgTiO₃-yBa(Zr_0.5Ti_0.5)O₃+zSm₂O₃The fired crystal grains of the lead-free piezoelectric ceramic were rhombohedral, and the average crystal grain size was 3 μm, replacing the previously fired tetragonal crystal grains of the KNN system.

The foregoing is a more detailed description of the invention in connection with specific preferred embodiments and it is not intended that the invention be limited to these specific details. For those skilled in the art to which the invention pertains, several simple deductions or substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.