阅读说明：本技术 一种无铅压电陶瓷材料及其制备方法 (Lead-free piezoelectric ceramic material and preparation method thereof ) 是由 方豪杰 贺亦文 张晓云 张斗 袁晰 于 2021-09-16 设计创作，主要内容包括：本发明涉及电子陶瓷材料领域,具体为一种无铅压电陶瓷材料及其制备方法,由以下化学式表示：(1-x)(K-(a)Na-(1-a))-(b)Li-(1-b)Nb-(c)Ta-(1-c)O-(3)+x(Na-(d)K-(1-d))-(e)Bi-(1-e)ZrO-(3)+y Lu-(2)O-(3)+z B-(2)O-(3)；其中,x为0.02-0.04,y为0.005-0.01,z为0.01-0.03；a为0.50-0.60,b为0.96-0.98,c为0.80-0.90,d为0.80-0.86,e为0.50-0.60,所制备的无铅压电陶瓷材料在目前KNN基无铅压电陶瓷性能中处于先进水平,具有广阔的应用前景。(The invention relates to the field of electronic ceramic materials, in particular to a lead-free piezoelectric ceramic material and a preparation method thereof, which are represented by the following chemical formula: (1-x) (K) a Na 1‑a ) b Li 1‑b Nb c Ta 1‑c O 3 +x(Na d K 1‑d ) e Bi 1‑e ZrO 3 +y Lu 2 O 3 +z B 2 O 3 (ii) a Wherein x is 0.02-0.04, y is 0.005-0.01, and z is 0.01-0.03; a is 0.50-0.60, b is 0.96-0.98, c is 0.80-0.90, d is 0.80-0.86, e is 0.50-0.60, the prepared leadless piezoelectric ceramic material is in an advanced level in the performance of the prior KNN-based leadless piezoelectric ceramic material, and has wide applicationAnd 4, application prospect.)

1. A lead-free piezoelectric ceramic material characterized by being represented by the following chemical formula:

(1-x)(K_aNa_1-a)_bLi_1-bNb_cTa_1-cO₃+x(Na_dK_1-d)_eBi_1-eZrO₃+y Lu₂O₃+z B₂O₃；

wherein x, y, z, a, b, c, d and e represent atomic percent, and y and z respectively represent Lu₂O₃And B₂O₃Is the compound (1-x) (K)_aNa_1-a)_bLi_1-bNb_cTa_1-cO₃+x(Na_dK_1-d)_eBi_1-eZrO₃The mass percentage of (A);

x is 0.02-0.04, y is 0.005-0.01, and z is 0.01-0.03;

a is 0.50-0.60, b is 0.96-0.98, c is 0.80-0.90, d is 0.80-0.86, and e is 0.50-0.60.

2. The lead-free piezoelectric ceramic material according to claim 1, wherein x is 0.02 to 0.025, y is 0.008 to 0.01, and z is 0.01 to 0.02.

3. The lead-free piezoelectric ceramic material according to claim 1, wherein x is 0.02, y is 0.01, and z is 0.02.

4. The lead-free piezoelectric ceramic material according to claim 1, wherein a is 0.50 to 0.55, b is 0.96 to 0.97, c is 0.80 to 0.85, d is 0.82 to 0.85, and e is 0.50 to 0.55.

5. The lead-free piezoelectric ceramic material according to claim 1, wherein a is 0.50, b is 0.97, c is 0.80, d is 0.82, and e is 0.50.

6. A method for preparing a lead-free piezoelectric ceramic material according to any one of claims 1 to 5, which comprises the following steps:

s1: weighing K according to the stoichiometric ratio of the chemical formula₂CO₃、Na₂CO₃、Nb₂O₅、Li₂CO₃、Ta₂O₅Mixing and ball-milling for 10-15h, heating to 700-;

s2: weighing K according to the stoichiometric ratio of the chemical formula₂CO₃、Na₂CO₃、ZrO₂、Bi₂O₃After mixing and ball milling for 10-15h, heating to 700-750 ℃ for presintering for 6-8h, recovering the room temperature, continuing ball milling for 10-15h, and heating to 780-800 ℃ for presintering for 5-10h to obtain second presintering powder;

s3: weighing the first pre-sintering powder, the second pre-sintering powder and Lu according to the stoichiometric ratio of the chemical formula₂O₃、B₂O₃Mixing and ball-milling for 20-40h, heating the mixed powder to 250 ℃ at 200 ℃, drying for 10-20h, and uniformly mixing with the binder to obtain slurry;

s4: injecting the slurry into a mold at the pressure of 5-10MPa, wherein the mold filling time is 25-50s, adding a direct current electric field of 1-2KV at two sides of the mold after the mold filling is finished, maintaining the pressure for 20-40min, and removing the electric field and demolding to obtain a blank;

s5: heating the blank to 150 ℃ for 40-60min after primary heating, heating to 550 ℃ for 2-5h after secondary heating, heating to 1350 ℃ for 2-5h after secondary heating, cooling to 800 ℃ for 1-3h after secondary heating, and cooling to room temperature;

s6: uniformly coating a silver layer on the upper surface and the lower surface of the sintered material as electrodes, keeping the temperature at 90-100 ℃ for 5-10h, then heating to 550 ℃ and 600 ℃ for heat preservation for 30-50min, cooling the furnace to room temperature, then immersing the furnace into silicon oil, and applying a direct current electric field of 3-6kv/mm for polarization for 20-50 min.

7. The method for preparing a lead-free piezoelectric ceramic material according to claim 6, wherein the binder in S3 is a polyvinyl alcohol solution having a mass concentration of 3 to 8%.

8. The method for preparing a lead-free piezoelectric ceramic material according to claim 7, wherein the mass ratio of the mixed powder to the polyvinyl alcohol solution in S3 is 1: 5-10.

9. The method for preparing a lead-free piezoelectric ceramic material according to claim 6, wherein in S5, the first temperature rise rate is 5-10 ℃/min, the second temperature rise rate is 5-10 ℃/min, and the third temperature rise rate is 1-3 ℃/min.

10. The method for preparing a lead-free piezoelectric ceramic material according to claim 6, wherein the temperature of the silicone oil is 80 to 120 ℃ at the time of polarization.

Technical Field

The invention relates to the field of electronic ceramic materials, in particular to a lead-free piezoelectric ceramic material and a preparation method thereof.

Background

The piezoelectric ceramic is a functional ceramic material capable of realizing interconversion of mechanical energy and electric energy. At present, the piezoelectric ceramic material widely used in the world is a lead-based piezoelectric ceramic represented by Pb (Zr, Ti) O, which has very good piezoelectric properties, a low sintering temperature and a high curie temperature (T)_c) However, the materials contain a large amount of lead, so that the atmospheric environment is polluted and the human health is damaged. With the improvement of the awareness of ecological environment protection and the requirement of sustainable development of human society, most countries forbid the use of lead-containing materials, and research and development of environment-friendly lead-free piezoelectric ceramic materials and corresponding preparation technologies to replace the traditional lead-based piezoelectric materials are in the forefront.

The lead-free piezoelectric ceramic systems reported or considered at present are mainly classified into 3 major classes of tungsten bronze lead-free piezoelectric ceramics, bismuth layered lead-free piezoelectric ceramics and perovskite lead-free piezoelectric ceramics in terms of crystal structure. Among them, potassium-sodium niobate (KNN) -based lead-free piezoelectric ceramics of perovskite structures are receiving much attention because of their high curie temperature and relatively excellent temperature stability, but their piezoelectric properties need to be improved, and if the piezoelectric properties of KNN-based piezoelectric ceramics at room temperature can be improved, their application prospects will inevitably be expanded.

Disclosure of Invention

The purpose of the invention is as follows: aiming at the defects or the improvement requirements of the prior art, the invention provides a lead-free piezoelectric ceramic material and a preparation method thereof.

The technical scheme adopted by the invention is as follows:

a lead-free piezoelectric ceramic material represented by the following chemical formula:

(1-x)(K_aNa_1-a)_bLi_1-bNb_cTa_1-cO₃+x(Na_dK_1-d)_eBi_1-eZrO₃+y Lu₂O₃+z B₂O₃；

wherein x, y, z, a, b, c, d and e represent atom hundredRatio of y and z represents Lu₂O₃And B₂O₃Is the compound (1-x) (K)_aNa_1-a)_bLi_1-bNb_cTa_1-cO₃+x(Na_dK_1-d)_eBi_1-eZrO₃The mass percentage of (A);

x is 0.02-0.04, y is 0.005-0.01, and z is 0.01-0.03;

a is 0.50-0.60, b is 0.96-0.98, c is 0.80-0.90, d is 0.80-0.86, and e is 0.50-0.60.

Further, x is 0.02-0.025, y is 0.008-0.01, and z is 0.01-0.02.

Further, x is 0.02, y is 0.01, and z is 0.02.

Further, a is 0.50-0.55, b is 0.96-0.97, c is 0.80-0.85, d is 0.82-0.85, and e is 0.50-0.55.

Further, a is 0.50, b is 0.97, c is 0.80, d is 0.82, and e is 0.50.

The preparation method of the lead-free piezoelectric ceramic material comprises the following steps:

s1: weighing K according to the stoichiometric ratio of the chemical formula₂CO₃、Na₂CO₃、Nb₂O₅、Li₂CO₃、Ta₂O₅Mixing and ball-milling for 10-15h, heating to 700-;

s2: weighing K according to the stoichiometric ratio of the chemical formula₂CO₃、Na₂CO₃、ZrO₂、Bi₂O₃After mixing and ball milling for 10-15h, heating to 700-750 ℃ for presintering for 6-8h, recovering the room temperature, continuing ball milling for 10-15h, and heating to 780-800 ℃ for presintering for 5-10h to obtain second presintering powder;

s3: weighing the first pre-sintering powder, the second pre-sintering powder and Lu according to the stoichiometric ratio of the chemical formula₂O₃、B₂O₃Mixing and ball-milling for 20-40h, heating the mixed powder to 250 ℃ at 200 ℃, drying for 10-20h, and uniformly mixing with the binder to obtain slurry;

s4: injecting the slurry into a mold at the pressure of 5-10MPa, wherein the mold filling time is 25-50s, adding a direct current electric field of 1-2KV at two sides of the mold after the mold filling is finished, maintaining the pressure for 20-40min, and removing the electric field and demolding to obtain a blank;

s5: heating the blank to 150 ℃ for 40-60min after primary heating, heating to 550 ℃ for 2-5h after secondary heating, heating to 1350 ℃ for 2-5h after secondary heating, cooling to 800 ℃ for 1-3h after secondary heating, and cooling to room temperature;

s6: uniformly coating a silver layer on the upper surface and the lower surface of the sintered material as electrodes, keeping the temperature at 90-100 ℃ for 5-10h, then heating to 550 ℃ and 600 ℃ for heat preservation for 30-50min, cooling the furnace to room temperature, then immersing the furnace into silicon oil, and applying a direct current electric field of 3-6kv/mm for polarization for 20-50 min.

Further, the binder in S3 is a polyvinyl alcohol solution with a mass concentration of 3-8%.

Further, the mass ratio of the mixed powder to the polyvinyl alcohol solution in S3 is 1: 5-10.

Further, in S5, the first heating rate is 5-10 ℃/min, the second heating rate is 5-10 ℃/min, and the third heating rate is 1-3 ℃/min.

Furthermore, the temperature of the silicone oil is 80-120 ℃ during polarization.

The invention has the beneficial effects that:

the invention provides a lead-free piezoelectric ceramic material, which reduces the orthogonal-tetragonal phase transition temperature of KNN-based lead-free piezoelectric ceramic by ion doping, so that a polycrystalline type transition region exists near room temperature, the electrical property of the ceramic at room temperature is obviously improved, meanwhile, a method of two-step presintering and injection molding pre-polarization under an external electric field is adopted during preparation, the piezoelectric property and the density of the ceramic material are enhanced, the piezoelectric constant of the prepared lead-free piezoelectric ceramic material is more than or equal to 260pC/N, the planar electromechanical coupling coefficient is more than or equal to 0.375, the dielectric loss is less than or equal to 0.023%, the lead-free piezoelectric ceramic material has good performance, is at an advanced level in the performance of the existing KNN-based lead-free piezoelectric ceramic, and has wide application prospect.

Drawings

Fig. 1 is an SEM image of a lead-free piezoelectric ceramic material prepared in example 1 of the present invention at room temperature.

Detailed Description

The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

Example 1:

a lead-free piezoelectric ceramic material represented by the following chemical formula:

0.98(K_0.50Na_0.50)_0.97Li_0.03Nb_0.80Ta_0.20O₃+0.02(Na_0.82K_0.18)_0.5Bi_0.5ZrO₃+0.01Lu₂O₃+0.02B₂O₃；

the preparation method comprises the following steps:

weighing K according to the metering ratio of the chemical formula₂CO₃、Na₂CO₃、Nb₂O₅、Li₂CO₃、Ta₂O₅Mixing and ball-milling for 15h, heating to 750 ℃ for presintering for 6h, recovering room temperature, continuing ball-milling for 15h, heating to 900 ℃ for presintering for 5h to obtain first presintering powder, weighing K according to the stoichiometric ratio of the chemical formula₂CO₃、Na₂CO₃、ZrO₂、Bi₂O₃Mixing and ball milling for 15h, heating to 750 deg.C for presintering for 6h, recovering room temperature, continuing ball milling for 15h, heating to 800 deg.C for presintering for 5h to obtain second presintering powder, and weighing the first presintering powder, the second presintering powder and Lu according to the stoichiometric ratio of the chemical formula₂O₃、B₂O₃Mixing and ball-milling for 40h, heating the mixed powder to 220 ℃, drying for 15h, then uniformly mixing the powder with a polyvinyl alcohol solution with the mass 10 times that of the mixed powder to obtain slurry, wherein the mass concentration of the polyvinyl alcohol solution is 5%, injecting the slurry into a mold at the pressure of 10MPa, filling the mold for 25s, adding a 1KV direct current electric field at two sides of the mold after the mold filling is finished, maintaining the pressure for 30min, removing the electric field, demolding to obtain a blank, heating the blank to 120 ℃ at the speed of 5 ℃/min for one time, keeping the temperature for 60min, heating to the speed of 5 ℃/min for two times, and heating to the speed of 5 ℃/min for two timesKeeping the temperature at 550 ℃ for 5h, heating to 1250 ℃ for 5h at the speed of 2 ℃/min for three times, cooling to 750 ℃ and keeping the temperature for 2h, cooling the furnace to room temperature, uniformly coating a silver layer on the upper surface and the lower surface of the sintered material to be used as an electrode, heating to 600 ℃ after the temperature is kept for 5h at 100 ℃ and keeping the temperature for 40min, cooling the furnace to room temperature, immersing into 100 ℃ silicon oil, and applying a direct current field with the voltage of 5kv/mm for polarization for 40 min.

Example 2:

a lead-free piezoelectric ceramic material represented by the following chemical formula:

0.98(K_0.50Na_0.50)_0.97Li_0.03Nb_0.80Ta_0.20O₃+0.02(Na_0.82K_0.18)_0.5Bi_0.5ZrO₃+0.01Lu₂O₃+0.02B₂O₃；

the preparation method comprises the following steps:

weighing K according to the metering ratio of the chemical formula₂CO₃、Na₂CO₃、Nb₂O₅、Li₂CO₃、Ta₂O₅Mixing and ball-milling for 10h, heating to 720 ℃ for presintering for 6h, recovering room temperature, continuing ball-milling for 15h, heating to 850 ℃ for presintering for 5h to obtain first presintering powder, and weighing K according to the stoichiometric ratio of the chemical formula₂CO₃、Na₂CO₃、ZrO₂、Bi₂O₃Mixing and ball milling for 12h, heating to 750 ℃ for presintering for 8h, recovering the room temperature, continuing ball milling for 10h, heating to 800 ℃ for presintering for 10h to obtain second presintering powder, and weighing the first presintering powder, the second presintering powder and Lu according to the stoichiometric ratio of the chemical formula₂O₃、B₂O₃Mixing and ball-milling for 20h, heating the mixed powder to 200 ℃, drying for 20h, then uniformly mixing with a polyvinyl alcohol solution with the mass 5 times that of the mixed powder to obtain a slurry, wherein the mass concentration of the polyvinyl alcohol solution is 3%, injecting the slurry into a mold at the pressure of 10MPa, filling the mold for 25s, adding a direct-current electric field of 1KV on two sides of the mold after the mold filling is finished, maintaining the pressure for 20min, removing the electric field, demolding to obtain a blank, heating the blank to 120 ℃ at the speed of 5 ℃/min once, and keeping the temperature for 6 DEG C0min, heating to 500 ℃ at the speed of 5 ℃/min for 5h twice, heating to 1350 ℃ at the speed of 1 ℃/min for 5h three times, cooling to 800 ℃ for 1h, cooling to room temperature, uniformly coating a silver layer on the upper and lower surfaces of the sintered material to be used as an electrode, heating to 600 ℃ after the temperature is maintained for 5h at 100 ℃ and then maintaining for 30min, cooling to room temperature in a furnace, immersing in 100 ℃ silicon oil, and applying a direct current field of 5kv/mm for polarization for 50 min.

Example 3:

a lead-free piezoelectric ceramic material represented by the following chemical formula:

0.98(K_0.50Na_0.50)_0.97Li_0.03Nb_0.80Ta_0.20O₃+0.02(Na_0.82K_0.18)_0.5Bi_0.5ZrO₃+0.01Lu₂O₃+0.02B₂O₃；

the preparation method comprises the following steps:

weighing K according to the metering ratio of the chemical formula₂CO₃、Na₂CO₃、Nb₂O₅、Li₂CO₃、Ta₂O₅Mixing and ball-milling for 10h, heating to 700 ℃ for presintering for 6h, recovering room temperature, continuing ball-milling for 10h, heating to 850 ℃ for presintering for 3h to obtain first presintering powder, and weighing K according to the stoichiometric ratio of the chemical formula₂CO₃、Na₂CO₃、ZrO₂、Bi₂O₃Mixing and ball milling for 10h, heating to 700 ℃ for presintering for 6h, recovering room temperature, continuing ball milling for 10h, heating to 780 ℃ for presintering for 5h to obtain second presintering powder, and weighing the first presintering powder, the second presintering powder and Lu according to the stoichiometric ratio of the chemical formula₂O₃、B₂O₃Mixing and ball-milling for 20h, heating the mixed powder to 200 ℃, drying for 10h, and then uniformly mixing with 5 times of polyvinyl alcohol solution in mass to obtain slurry, wherein the mass concentration of the polyvinyl alcohol solution is 3%, injecting the slurry into a mold at the pressure of 5MPa, filling the mold for 25s, adding 1KV direct-current electric field on two sides of the mold after the mold filling is finished, maintaining the pressure for 20min, removing the electric field, demolding to obtain a blank, and processing the blank at the temperature of 5 DEG CHeating to 120 ℃ at a speed of/min for 40min, heating to 500 ℃ at a speed of 5 ℃/min for 2h, heating to 1150 ℃ at a speed of 1 ℃/min for three times for 2h, cooling to 700 ℃ for 1h, cooling to room temperature, uniformly coating a silver layer on the upper surface and the lower surface of the sintered material as electrodes, heating to 550 ℃ after 5h at 90 ℃ for 30min, cooling to room temperature, immersing in 80 ℃ silicon oil, and applying a direct current electric field with the intensity of 3kv/mm for polarization for 20 min.

Example 4:

a lead-free piezoelectric ceramic material represented by the following chemical formula:

0.98(K_0.50Na_0.50)_0.97Li_0.03Nb_0.80Ta_0.20O₃+0.02(Na_0.82K_0.18)_0.5Bi_0.5ZrO₃+0.01Lu₂O₃+0.02B₂O₃；

the preparation method comprises the following steps:

weighing K according to the metering ratio of the chemical formula₂CO₃、Na₂CO₃、Nb₂O₅、Li₂CO₃、Ta₂O₅Mixing and ball-milling for 15h, heating to 750 ℃ for presintering for 8h, recovering to room temperature, continuing ball-milling for 15h, heating to 900 ℃ for presintering for 5h to obtain first presintering powder, and weighing K according to the stoichiometric ratio of the chemical formula₂CO₃、Na₂CO₃、ZrO₂、Bi₂O₃Mixing and ball milling for 15h, heating to 750 ℃ for presintering for 8h, recovering the room temperature, continuing ball milling for 15h, heating to 800 ℃ for presintering for 10h to obtain second presintering powder, and weighing the first presintering powder, the second presintering powder and Lu according to the stoichiometric ratio of the chemical formula₂O₃、B₂O₃And mixing and ball-milling for 40h, heating the mixed powder to 250 ℃, drying for 20h, and then uniformly mixing with a polyvinyl alcohol solution with the mass 10 times that of the mixed powder to obtain slurry, wherein the mass concentration of the polyvinyl alcohol solution is 8%, injecting the slurry into a mold at the pressure of 10MPa, filling the mold for 50s, adding a direct-current electric field of 1KV at two sides of the mold after the mold filling is finished, maintaining the pressure for 40min, and removing the electric field to remove the electric fieldAnd (2) performing die casting to obtain a blank, heating the blank to 150 ℃ at the speed of 10 ℃/min for 60min at one time, heating to 550 ℃ at the speed of 10 ℃/min for 5h at a second time, heating to 1350 ℃ at the speed of 3 ℃/min for 5h at a third time, cooling to 800 ℃ for 3h, cooling in a furnace to room temperature, uniformly coating a layer of silver layer on the upper surface and the lower surface of the sintered material as electrodes, heating to 600 ℃ for 50min after 10h at 100 ℃, cooling in the furnace to room temperature, immersing in 120 ℃ silicon oil, and applying a direct current electric field with the voltage of 6kv/mm for polarization for 50 min.

Example 5:

a lead-free piezoelectric ceramic material represented by the following chemical formula:

0.98(K_0.50Na_0.50)_0.97Li_0.03Nb_0.80Ta_0.20O₃+0.02(Na_0.82K_0.18)_0.5Bi_0.5ZrO₃+0.01Lu₂O₃+0.02B₂O₃；

the preparation method comprises the following steps:

weighing K according to the metering ratio of the chemical formula₂CO₃、Na₂CO₃、Nb₂O₅、Li₂CO₃、Ta₂O₅Mixing and ball-milling for 10h, heating to 750 ℃ for presintering for 6h, recovering room temperature, continuing ball-milling for 15h, heating to 850 ℃ for presintering for 5h to obtain first presintering powder, weighing K according to the stoichiometric ratio of the chemical formula₂CO₃、Na₂CO₃、ZrO₂、Bi₂O₃Mixing and ball milling for 10h, heating to 750 ℃ for presintering for 6h, recovering room temperature, continuing ball milling for 15h, heating to 780 ℃ for presintering for 10h to obtain second presintering powder, and weighing the first presintering powder, the second presintering powder and Lu according to the stoichiometric ratio of the chemical formula₂O₃、B₂O₃Mixing and ball-milling for 20h, heating the mixed powder to 250 ℃, drying for 10h, and then uniformly mixing with a polyvinyl alcohol solution with the mass 10 times that of the mixed powder to obtain slurry, wherein the mass concentration of the polyvinyl alcohol solution is 3%, injecting the slurry into a mold at the pressure of 10MPa, filling the mold for 25s, and adding 1KV on two sides of the mold after the mold filling is finishedMaintaining the pressure of a direct current electric field for 20min, removing the electric field, demolding to obtain a blank, heating the blank to 120 ℃ at the speed of 10 ℃/min for 60min, heating to 550 ℃ at the speed of 5 ℃/min for 2h twice, heating to 1150 ℃ at the speed of 3 ℃/min for three times for 5h, cooling to 700 ℃ for 3h, cooling to room temperature in a furnace, uniformly coating a silver layer on the upper surface and the lower surface of the sintered material to be used as electrodes, heating to 550 ℃ after 10h of 90 ℃ for 50min, cooling to room temperature in the furnace, immersing in 80 ℃ silicon oil, and applying a direct current electric field of 6kv/mm for polarization for 20 min.

Comparative example 1

Comparative example 1 is essentially the same as example 1, except that Lu is not added₂O₃。

Comparative example 2

Comparative example 2 is essentially the same as example 1, except that B is not added₂O₃。

Comparative example 3

Comparative example 3 is substantially the same as example 1 except that two prefiring is changed to one prefiring in preparation.

The preparation method comprises the following steps:

weighing K according to the metering ratio of the chemical formula₂CO₃、Na₂CO₃、Nb₂O₅、Li₂CO₃、Ta₂O₅Mixing, ball-milling for 15h, heating to 900 deg.C, presintering for 5h to obtain first presintering powder, and weighing K according to the stoichiometric ratio of the chemical formula₂CO₃、Na₂CO₃、ZrO₂、Bi₂O₃Mixing, ball milling for 15h, heating to 800 deg.C, presintering for 5h to obtain second presintering powder, and weighing the first presintering powder, the second presintering powder and Lu according to the stoichiometric ratio of the chemical formula₂O₃、B₂O₃Mixing and ball-milling for 40h, heating the mixed powder to 220 ℃, drying for 15h, and then uniformly mixing with a polyvinyl alcohol solution with the mass 10 times that of the mixed powder to obtain slurry, wherein the mass concentration of the polyvinyl alcohol solution is 5%, injecting the slurry into a mold at the pressure of 10MPa, filling the mold for 25s, and adding 1K to the two sides of the mold after the mold filling is finishedAnd (2) maintaining the voltage of the direct current electric field of V for 30min, removing the electric field, demolding to obtain a blank, heating the blank to 120 ℃ at the speed of 5 ℃/min for 60min, heating to 550 ℃ at the speed of 5 ℃/min for 5h twice, heating to 1250 ℃ at the speed of 2 ℃/min for three times for 5h, cooling to 750 ℃ for 2h, cooling to room temperature in a furnace, uniformly coating a silver layer on the upper surface and the lower surface of the sintered material to be used as an electrode, heating to 600 ℃ after the temperature is maintained for 5h at 100 ℃, keeping the temperature for 40min, cooling to room temperature in the furnace, immersing in 100 ℃ silicon oil, and applying a direct current electric field of 5kv/mm for polarization for 40 min.

Comparative example 4

Comparative example 4 is substantially the same as example 1 except that no electric field is applied after the mold filling is completed.

The preparation method comprises the following steps:

weighing K according to the metering ratio of the chemical formula₂CO₃、Na₂CO₃、Nb₂O₅、Li₂CO₃、Ta₂O₅Mixing and ball-milling for 15h, heating to 750 ℃ for presintering for 6h, recovering room temperature, continuing ball-milling for 15h, heating to 900 ℃ for presintering for 5h to obtain first presintering powder, weighing K according to the stoichiometric ratio of the chemical formula₂CO₃、Na₂CO₃、ZrO₂、Bi₂O₃Mixing and ball milling for 15h, heating to 750 deg.C for presintering for 6h, recovering room temperature, continuing ball milling for 15h, heating to 800 deg.C for presintering for 5h to obtain second presintering powder, and weighing the first presintering powder, the second presintering powder and Lu according to the stoichiometric ratio of the chemical formula₂O₃、B₂O₃Mixing and ball-milling for 40h, heating the mixed powder to 220 ℃, drying for 15h, then uniformly mixing with a polyvinyl alcohol solution with the mass 10 times that of the mixed powder to obtain slurry, wherein the mass concentration of the polyvinyl alcohol solution is 5%, injecting the slurry into a mold at the pressure of 10MPa, filling the mold for 25s, keeping the pressure for 30min to obtain a blank, heating the blank to 120 ℃ at the speed of 5 ℃/min for 60min at one time, heating to 550 ℃ at the speed of 5 ℃/min for 5h at a second time, heating to 1250 ℃ at the speed of 2 ℃/min for 5h at a third time, cooling to 750 ℃ for 2h, cooling the furnace to room temperature, and sintering to obtain the productUniformly coating a silver layer on the upper surface and the lower surface of the bonded material to be used as electrodes, keeping the temperature at 100 ℃ for 5 hours, then heating to 600 ℃, keeping the temperature for 40 minutes, cooling the furnace to room temperature, then immersing the furnace into silicone oil at 100 ℃, and applying a direct current electric field of 5kv/mm for polarization for 40 minutes.

And (3) performance testing:

the piezoelectric constant is a parameter characterizing the performance of a piezoelectric material, and reflects the conversion capability of a piezoelectric body to convert mechanical energy into electric energy (positive piezoelectric effect) or convert electric energy into mechanical energy (inverse piezoelectric effect). The larger the piezoelectric constant is, the stronger the capability of the material for mutually converting mechanical energy and electric energy is, the better the coupling effect is, and the ZJ-3 type quasi-static d is used₃₃The measuring instrument measures the piezoelectric constant of the sample;

testing the resonance and anti-resonance frequency of the sample at room temperature and the parameters of equivalent resistance, equivalent capacitance and the like at 1kHz by using an impedance analyzer, and calculating the planar electromechanical coupling coefficient K of the sample_pAnd a dielectric loss tan δ.

The lead-free piezoelectric ceramic materials prepared in examples 1 to 5 and comparative examples 1 to 4 were subjected to the performance test, and the test results are shown in the following table 1:

TABLE 1

As can be seen from the above table 1, the lead-free piezoelectric ceramic material prepared by the invention has a piezoelectric constant of not less than 260pC/N, a planar electromechanical coupling coefficient of not less than 0.375, and a dielectric loss of not more than 0.023%, has good performance, is at an advanced level in the performance of the existing KNN-based lead-free piezoelectric ceramic, and has a wide application prospect.

The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.