CN115959906A - A strontium niobate-based perovskite layered structure lead-free piezoelectric ceramic and its preparation method - Google Patents

Abstract

The invention relates to a strontium niobate-based perovskite layered structure lead-free piezoelectric ceramic and a preparation method thereof. The chemical composition of the strontium niobate-based perovskite layered structure lead-free piezoelectric ceramic is Sr _{2‑ x} Nb ₂ O ₇ Wherein x is more than 0 and less than or equal to 0.16.

Description

A strontium niobate-based perovskite layered structure lead-free piezoelectric ceramic and a preparation method thereof

Technical Field

The invention relates to a strontium niobate-based perovskite layered structure lead-free piezoelectric ceramic material and a preparation method thereof, belonging to the field of preparation of piezoelectric ceramic materials.

Background Art

High-temperature piezoelectric vibration sensors play an irreplaceable and important role in monitoring the working status of key components such as the intake duct, casing, turbine blades of my country's aviation engines, as well as the fuel assemblies, control rods, cooling pipes of nuclear reactors, but this aspect is blank in China. Therefore, my country urgently needs to independently develop high-stability high-temperature piezoelectric vibration sensors to break the monopoly of international technology blockade. Piezoelectric materials are the core sensitive materials of high-temperature piezoelectric vibration sensors. The high-temperature piezoelectric ceramic materials developed in my country can basically meet the use requirements of 260℃ and 482℃ piezoelectric vibration sensors, but there is still little research on high-temperature piezoelectric ceramic materials at higher temperatures of 650℃ and above, which greatly restricts the development process of high-temperature piezoelectric vibration sensors in my country. Perovskite layered structure piezoelectric ceramics are important candidate materials for high-temperature vibration sensors of 650℃ and above due to their high stability and high high-temperature resistivity.

However, the main problems faced in the development of perovskite layered piezoelectric ceramics include: (1) the dielectric breakdown field strength is relatively low relative to the coercive field strength, and the piezoelectric ceramics are difficult to polarize; (2) the piezoelectric coefficient is relatively low. These factors greatly restrict the application of perovskite layered piezoelectric ceramics in the field of high-temperature piezoelectric vibration sensors.

At present, the piezoelectricity of perovskite layered piezoelectric ceramic materials is improved by solid solution of the second component, ion doping to optimize the composition design, and texturing process to control the microstructure. For example, by introducing the perovskite structure Na _0.5 Bi _0.5 TiO ₃ piezoelectric ceramics into Sr ₂ Nb ₂ O ₇ , the piezoelectric coefficient d ₃₃ is increased to 1.0pC/N; after adjusting the microstructure through the texturing spark plasma sintering process, the piezoelectric coefficient d ₃₃ of the perovskite structure piezoelectric ceramic can be increased by 1.5pC/N. However, texturing processes such as hot pressing, hot forging, rapid plasma sintering, etc. are relatively complex and have poor repeatability. Although the piezoelectric properties of perovskite layered piezoelectric ceramics have been improved to a certain extent by ion doping, solid solution of the second component, and process improvement, the piezoelectric coefficient is still relatively small. Therefore, how to improve the dielectric breakdown field strength and piezoelectric coefficient of perovskite layered structure materials while maintaining the high-temperature resistivity of perovskite layered structure piezoelectric ceramics is the research focus and key problem in the application field of high-temperature piezoelectric ceramics.

Summary of the invention

In view of the above problems, in order to maintain the high-temperature resistivity of perovskite layered structure piezoelectric ceramics and synergistically improve their piezoelectric coefficient, the present invention provides a method based on non-stoichiometric A-site Sr ion deficiency, by adjusting the inclination and rotation of the oxygen octahedron in the perovskite layered structure and the size of the bandgap width, a lead-free high-temperature piezoelectric ceramic with a high piezoelectric coefficient, a high dielectric breakdown field strength and a high high-temperature resistivity is obtained, which meets the requirements of high-temperature piezoelectric ceramic materials for high-temperature piezoelectric vibration sensors and promotes the application of perovskite layered structure piezoelectric ceramic materials in high-temperature fields of 650°C and above.

In one aspect, the present invention provides a strontium niobate-based perovskite layered structure lead-free piezoelectric ceramic, wherein the chemical composition of the strontium niobate-based perovskite layered structure lead-free piezoelectric ceramic is Sr _2-x Nb ₂ O ₇ , wherein 0＜x≤0.16.

The perovskite layered structure piezoelectric ceramic material based on non-stoichiometric ratio of A-site Sr ion deficiency of the present invention has excellent piezoelectric properties, resistance properties and breakdown properties, and is expected to be applied in high-temperature fields with temperatures higher than 650°C and above.

Preferably, the piezoelectric coefficient of the strontium niobate-based perovskite layered structure lead-free piezoelectric ceramic tested by a ZJ-3A quasi-static d33 tester at room temperature 25° C. is (0.8-2.1) pC/N.

Preferably, the direct current resistivity of the niobium-strontium-based perovskite layered lead-free piezoelectric ceramic at 700° C. is tested by using an HP4339B high temperature resistance tester and is 6.7×10 ⁶ to 1.1×10 ⁷ Ω·cm.

Preferably, the dielectric breakdown field strength of the strontium niobate-based perovskite layered structure lead-free piezoelectric ceramic tested by using an SD-DC 200 kV DC voltage generator is 206.2 kV/cm to 435.7 kV/cm.

On the other hand, the present invention provides a method for preparing a strontium niobate-based perovskite layered structure lead-free piezoelectric ceramic, comprising:

(1) SrCO ₃ and Nb ₂ O ₅ are weighed and mixed according to the stoichiometric ratio of Sr _2-x Nb ₂ O ₇ , and pre-sintered to obtain ceramic powder;

(2) The ceramic powder and the binder are mixed, and then granulated, aged, pressed and molded to obtain a ceramic body.

(3) The ceramic body is placed in a high-temperature furnace, and the obtained ceramic powder is used to cover the ceramic body, and after sintering, the strontium niobate-based perovskite layered structure lead-free piezoelectric ceramic is obtained.

Preferably, in step (1), the mixing method is ball milling; the parameters of the ball milling mixing include: the ball milling medium is agate balls; the ball milling speed is 240 to 360 rpm, and the time is 4 to 6 hours; the mass ratio of raw material: ball milling medium: alcohol is 1:2:(1.8 to 2.0).

Preferably, in step (1), the pre-sintering temperature is 1000-1300°C, and the holding time does not exceed 24 hours; preferably, the pre-sintering heating rate is ≤2°C/min.

Preferably, in step (2), the binder is at least one of polyvinyl alcohol, polyvinyl butyral and polyvinylidene fluoride, and the amount of the binder added is 6-7wt.% of the weight of the ceramic powder.

Preferably, in step (2), the temperature of the plastic discharge is 700-800°C, and the insulation time is 1-3 hours; preferably, the heating rate of the plastic discharge is ≤2°C/min.

Preferably, in step (3), the sintering temperature is 1350-1500° C., and the holding time does not exceed 24 hours; preferably, the sintering heating rate is ≤2° C./min.

Preferably, the obtained strontium niobate-based perovskite layered structure lead-free piezoelectric ceramic sheet is processed into a desired size, and then ultrasonically cleaned, screen-printed with a metal electrode, dried and fired; the metal electrode is silver or platinum; the temperature of the fired metal electrode is 1000-1200°C, and the insulation time is 5-40 minutes.

Beneficial effects:

The strontium niobate-based perovskite layered structure lead-free piezoelectric ceramics proposed in the present invention have a piezoelectric coefficient of (0.8-2.1) pC/N at room temperature 25°C, a resistivity of 6.7×10 ⁶ -1.1×10 ⁷ Ω·cm at 700°C, and a dielectric breakdown field strength of 206.2 kV/cm-435.7 kV/cm, providing a new method and new material composition design for preparing perovskite layered piezoelectric ceramics for high-temperature vibration sensors that meet the requirements of temperatures above 650°C.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows the dielectric breakdown field strength of Sr _2-x Nb2O7 ceramics with different Sr deficiencies at room temperature;

Figure 2 shows the piezoelectric coefficient d ₃₃ of Sr _2-x Nb ₂ O ₇ ceramics with different Sr deficiencies at room temperature.

DETAILED DESCRIPTION

The present invention is further described below by the following embodiments. It should be understood that the following embodiments are only used to illustrate the present invention, but not to limit the present invention.

In the present disclosure, a design concept based on a non-stoichiometric ratio of A-site Sr ion deficiency is adopted to improve the high piezoelectric properties, high temperature high resistivity and high dielectric breakdown field strength of niobate-based perovskite layered structure piezoelectric ceramics.

In one embodiment of the present invention, the chemical composition of the perovskite layered structure piezoelectric ceramic is: Sr _2-x Nb ₂ O ₇ , wherein 0<x≤0.16, preferably x=0.02-0.16.

In an optional embodiment, the depolarization temperature of the perovskite layered piezoelectric ceramic based on a non-stoichiometric ratio of A-site Sr ion deficiency is as high as 1100°C, the component with x=0.04 has the highest piezoelectric coefficient and good temperature stability, the piezoelectric coefficient maintains a high value in the range of 25°C-1100°C, the piezoelectric coefficient at 1100°C is still 2.1pC/N, and the breakdown field strength is 264.96kV/cm. The high temperature resistivity at 700°C meets the needs of practical use and is 1.1×107Ω·cm.

The following is an exemplary description of a method for preparing a strontium niobate-based perovskite layered structure lead-free piezoelectric ceramic.

Ingredients. The ceramic powder is prepared by a solid phase method, with SrCO ₃ powder and Nb ₂ O ₅ powder as raw materials and prepared according to a stoichiometric ratio.

Mixing. The raw material powder is ball-milled once to obtain a mixed powder. As an example of ball milling, the ball mill is a wet planetary ball mill, the ball milling time is 4 hours, the rotation speed is 360 rpm, the mass ratio of raw material: ball: alcohol is 1:2: (1.8-2.0), and the ball milling medium is agate ball.

Pre-sintering synthesis. The mixed powder is pre-sintered to obtain ceramic powder. The synthesis temperature of the mixed powder can be 1000°C to 1300°C. The insulation time of the synthesis temperature is no more than 24 hours, preferably 1 to 3 hours. As an example, the temperature is increased to 1200°C at a heating rate not higher than 2°C/min, kept at this temperature for 1 to 3 hours, and cooled to room temperature with the furnace.

Fine grinding and granulation. The ceramic powder is finely ground and dried, and then a binder is added to granulate to obtain granulated powder. The binder may be polyvinyl alcohol (PVA) or the like. The amount of binder added may be 6 to 7 wt.% of the weight of the ceramic powder. The parameters of the fine grinding include: the ball milling medium is agate balls; the ball milling speed is 240 to 360 rpm, and the time is 4 to 6 hours; the mass ratio of raw material: ball milling medium: alcohol is 1:2: (1.8 to 2.0). As an example, the fine grinding is wet planetary ball milling, the ball milling time is 4 hours, the speed is 360 rpm, the mass ratio of raw material: ball: alcohol is 1:2: (1.6 to 1.8), and the ball milling medium is agate balls.

Molding. The granulated powder is pressed and molded after aging to obtain a ceramic green body. The aging temperature can be 0-40°C and the time can be ≤48 hours, in order to enhance the fluidity of the powder. The molding method can be isostatic pressing and/or dry pressing.

The ceramic green body is heated and molded to obtain a ceramic green body. As an example, the temperature is increased to 700-800°C at a heating rate of no more than 2°C/min and kept at this temperature for 1-3 hours.

Sintering. Place the ceramic body into a high-temperature furnace, cover the ceramic body with a ceramic powder having the same composition as the obtained one, and then sinter under certain conditions to obtain the ceramic sheet. The sintering temperature may be 1350°C to 1500°C. The sintering holding time does not exceed 24 hours, preferably 1 to 3 hours. As an example, heat up to 1350 to 1400°C at a heating rate not higher than 2°C/min, keep warm for 1 to 3 hours, and cool to room temperature with the furnace.

Electrode preparation: The sintered ceramic sheet is processed into the required size, ultrasonically cleaned, screen-printed with silver, dried, and calcined to obtain the piezoelectric ceramic material. The calcination conditions can be 1000-1200°C, and the holding time can be 5-40 minutes.

The following further examples are given to explain the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention belong to the scope of protection of the present invention. The specific process parameters and the like in the following examples are only examples within a suitable range, that is, those skilled in the art can make selections within a suitable range through the description of this article, and are not limited to the specific values exemplified below. The following percentages refer to mass percentages unless otherwise specified.

Embodiment 1:

A-site defective perovskite layered structure Sr _2-x Nb ₂ O ₇ ceramics were prepared by solid phase reaction method. The molar ratio of Sr defect was 0, 0.04, 0.08 and 0.12 respectively. SrCO ₃ and Nb ₂ O ₅ were used as raw materials, and the materials were mixed by wet ball milling method. The raw materials: grinding medium: alcohol = 1:2:1.8 were mixed for 4 hours to make them uniform. After drying at 100℃, the mixture was passed through a 30-mesh sieve and formed under a pressure of 3MPa. The temperature was raised to 1200℃ at a heating rate of 2℃/min and kept at this temperature for 2 hours to synthesize the required ceramic powder.

The obtained ceramic powder is ground, passed through a 30-mesh sieve, and then finely ground by a wet ball mill. The powder is mixed for 4 hours at a mass ratio of ceramic powder: grinding medium: alcohol meter = 1:2:1.5 to make it uniformly mixed. The obtained powder is dried, 6 wt.% of PVA binder is added, granulated, formed under a pressure of 5 MPa, aged for 24 hours, passed through a 40-mesh sieve, and pressed into a disc with a diameter of 13 mm under a pressure of 1.0-1.2 MPa. The disc is then heated to 800°C in a low-temperature furnace, kept warm for 60 minutes, and extruded to obtain a ceramic green body.

The ceramic body was placed in an alumina crucible, heated to 1400°C at a heating rate of 2°C/min, kept at that temperature for 2 hours, and then cooled in the furnace to obtain a ceramic sheet.

The sintered ceramic sheet was ground to a thickness of 0.15 mm, cleaned, dried, screen-printed with platinum slurry, dried again, and heated to 1200° C. at a heating rate of 2° C./min. The platinum was sintered for 30 minutes to obtain the piezoelectric ceramic material.

The piezoelectric properties, breakdown properties and other properties of the polarized ceramics were tested, and the results are shown in Figure 1 and Table 1.

Table 1 is a comparison of the performance parameters of Sr _2-x Nb ₂ O ₇ ceramics with different Sr deficiencies prepared by the present invention:

Claims (10)

1. A strontium niobate-based perovskite layered structure lead-free piezoelectric ceramic, characterized in that the chemical composition of the strontium niobate-based perovskite layered structure lead-free piezoelectric ceramic is Sr _2-x Nb ₂ O ₇ , wherein 0＜x≤0.16. 2. The strontium niobate-based perovskite layered structure lead-free piezoelectric ceramic according to claim 1, characterized in that the piezoelectric coefficient of the strontium niobate-based perovskite layered structure lead-free piezoelectric ceramic at room temperature 25°C is (0.8-2.1) pC/N. 3 . The strontium niobate-based perovskite layered structure lead-free piezoelectric ceramic according to claim 1 , wherein the direct current resistivity of the strontium niobate-based perovskite layered structure lead-free piezoelectric ceramic at 700° C. is 6.7×10 ⁶ to 1.1×10 ⁷ Ω·cm. 4. The strontium niobate-based perovskite layered structure lead-free piezoelectric ceramic according to claim 1, characterized in that the dielectric breakdown field strength of the strontium niobate-based perovskite layered structure lead-free piezoelectric ceramic is 206.2 kV/cm to 435.7 kV/cm. 5. A method for preparing the strontium niobate-based perovskite layered structure lead-free piezoelectric ceramic according to any one of claims 1 to 4, characterized in that it comprises: (1) SrCO ₃ and Nb ₂ O ₅ are used as raw materials, weighed and mixed according to the stoichiometric ratio of Sr _2-x Nb ₂ O ₇ , and pre-sintered to obtain ceramic powder; (2) The ceramic powder and the binder are mixed, and then granulated, aged, pressed and molded to obtain a ceramic body; (3) The ceramic body is placed in a high-temperature furnace, and the obtained ceramic powder is used to cover the ceramic body. After sintering, the strontium niobate-based perovskite layered structure lead-free piezoelectric ceramic is obtained. 6. The preparation method according to claim 5 is characterized in that in step (1), the mixing method is ball milling mixing; the parameters of the ball milling mixing include: the ball milling medium is agate balls; the ball milling speed is 240 to 360 rpm, and the time is 4 to 6 hours; the mass ratio of raw material: ball milling medium: alcohol is 1:2:(1.8 to 2.0). 7. The preparation method according to claim 5, characterized in that in step (1), the pre-sintering temperature is 1000-1300°C, and the insulation time does not exceed 24 hours; preferably, the pre-sintering heating rate is ≤2°C/min. 8. The preparation method according to claim 5, characterized in that in step (2), the binder is at least one of polyvinyl alcohol, polyvinyl butyral and polyvinylidene fluoride, and the amount of the binder added is 6-7wt.% of the weight of the ceramic powder; The temperature of the plastic discharge is 700-800°C, and the insulation time is 1-3 hours; preferably, the heating rate of the plastic discharge is ≤2°C/minute. 9. The preparation method according to claim 5, characterized in that in step (3), the sintering temperature is 1350-1500°C, and the holding time is no more than 24 hours; preferably, the sintering heating rate is ≤2°C/min. 10. The preparation method according to claim 5 is characterized in that the obtained strontium niobate-based perovskite layered structure lead-free piezoelectric ceramic sheet is processed into a desired size, and then ultrasonically cleaned, screen-printed with a metal electrode, dried and fired; the metal electrode is silver or platinum; the temperature of the fired metal electrode is 1000-1200°C, and the insulation time is 5-40 minutes.

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