Potassium sodium niobate based textured piezoelectric ceramics with high curie temperature and temperature stability and method of making same

Abstract

The present application relates to a potassium sodium niobate based textured piezoelectric ceramic with high Curie temperature and temperature stability, and a preparation method thereof, the textured piezoelectric ceramic has a general chemical formula of (0.99-x)((K 0.5 Na 0.5 )(Nb 0.98 Ta 0.02 )O3)‑0.01(Bi(Ni 0.67 Nb 0.33 )O3)‑x(Bi 0.5 K 0.5 )HfO3+3wt.%NaNbO3, 0≤x≤0.04; the method comprises a solid phase synthesis method, a two-step molten salt method combined with a separation method, a template grain growth method, a casting process, a hot pressing process, a glue removal process, a two-step sintering process, a silver sintering process and a polarization process. Compared with the prior art, the present application can obtain a lead-free textured piezoelectric ceramic with high Curie temperature and high piezoelectric performance by the solid phase synthesis method, the template grain growth method combined with the casting process and the two-step sintering process, more importantly, the ceramic exhibits a single tetragonal phase structure, has high positive and inverse piezoelectric coefficients, and the piezoelectric coefficient and the inverse piezoelectric coefficient have small change rates in a wide temperature range, and has excellent temperature stability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of functional ceramics, and relates to a potassium-sodium niobate-based textured piezoelectric ceramic material with high Curie temperature and good temperature stability and a preparation method thereof. BACKGROUND

[0002] Piezoelectric ceramics are information functional ceramic materials capable of realizing mechanical energy and electrical energy conversion, are core materials for manufacturing machine-electric conversion functional electronic components, and have been widely applied to medical imaging, acoustic sensors, acoustic transducers, ultrasonic motors and the like.

[0003] At present, lead titanate and lead zirconate titanate-based piezoelectric ceramics have occupied the main share of the piezoelectric material market due to high piezoelectric coefficients and high temperature stability, but both of the two ceramics use lead oxide as the main raw material, and lead as a heavy metal can cause serious damage to human beings and the ecological environment in the production, use and post-disposal processes. After the European Union issued the Directive on the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment in 2006, the application of lead-containing materials in electronic products has been prohibited. Since then, many countries such as the United States and Japan have also issued similar decrees to prohibit the application of lead-containing electronic devices, and China has also issued the Management Method for Pollution Prevention and Control of Electronic Information Products. Therefore, the development of lead-free piezoelectric materials with high performance and high temperature stability comparable to traditional PZT-based piezoelectric ceramic materials has important strategic significance and economic value in the application of electronic components.

[0004] Potassium-sodium niobate-based ((K,Na)NbO3, KNN) ceramics are considered to be one of the most promising lead-free piezoelectric ceramic candidates due to their relatively good comprehensive performance. Although pure potassium-sodium niobate lead-free piezoelectric ceramics have a high Curie temperature (~430℃), their ferroelectric and piezoelectric properties are poor. The piezoelectric coefficient d 33 of the (K,Na)NbO3 ceramics obtained by the traditional solid-phase sintering method without component modification is generally 80-120pC / N, which is still far from the piezoelectric performance of lead-based ceramics. At present, the research on potassium-sodium niobate-based lead-free piezoelectric ceramics mainly focuses on improving the electrical properties, mainly by constructing a multiphase coexistence near room temperature to exhibit excellent piezoelectric properties, making it one of the most promising alternative materials. However, the phase boundary of potassium-sodium niobate-based lead-free piezoelectric ceramics has a strong piezoelectric temperature dependence. When the environmental temperature deviates from the phase transition temperature, the piezoelectric properties of potassium-sodium niobate-based ceramics rapidly decrease, resulting in poor temperature stability. The multi-layer composite ceramic composed of two different chemical composition textured thick films stacked in different proportions in patent CN117125981A maintains good piezoelectric properties in a wide temperature range, but the multi-layer ceramic is prone to delamination and cracking during the sintering process.

[0005] The application patent CN114436653A discloses a high anti-reduction potassium sodium niobate-based lead-free piezoelectric ceramic with high inverse piezoelectricity and high stability, the inverse piezoelectric coefficient is only 470 pm / V under 20 kV / cm, the stability changes by 10% within room temperature to 155°C, and the stability of the piezoelectric coefficient is not mentioned.

[0006] CN116768623A discloses a potassium sodium niobate-based textured piezoelectric ceramic with temperature stability and a preparation method thereof, high piezoelectric coefficient and excellent temperature stability are obtained, but only the temperature stability of small signal piezoelectric coefficient d 33 is reported, and the value and stability of large signal inverse piezoelectric coefficient d 33 * are not explicitly shown.

[0007] It can be seen that it is a challenge to achieve high piezoelectric coefficient and high stability of inverse piezoelectric coefficient at the same time, but both of them are essential for practical application. Especially, the stability of inverse piezoelectric coefficient is also crucial for some electric actuators that need to be used in a wide temperature range.

[0008] In the reports about potassium sodium niobate-based piezoelectric ceramics, in order to obtain high piezoelectricity, the Curie temperature is reduced when the potassium sodium niobate-based ceramic is doped and modified, it is difficult to obtain high Curie temperature and high piezoelectric coefficient at the same time, and in most reports, in order to improve the piezoelectric performance, the piezoelectric ceramic is in a multi-phase coexistence state at room temperature, and in the temperature change test, the phase ratio will change, which will cause a large decline in piezoelectric performance, and it is relatively difficult to obtain a ceramic with stable positive and inverse piezoelectric coefficients. Relatively speaking, single-phase ceramics can well avoid this problem, but the piezoelectric performance of single-phase ceramics is often low, so how to appropriately improve the piezoelectric performance on the basis of single-phase ceramics is also a direction worthy of research. SUMMARY

[0009] The purpose of the present application is to overcome at least one of the defects existing in the prior art and provide a potassium sodium niobate-based textured piezoelectric ceramic with high Curie temperature and temperature stability and a preparation method thereof. The present application can obtain a lead-free textured piezoelectric ceramic with high piezoelectric performance by solid phase synthesis method, template grain growth method combined with casting process and two-step sintering process, and the ceramic has good positive and inverse piezoelectric coefficients while being in a single tetragonal phase structure, and the single phase structure is beneficial to the temperature stability of the ceramic, specifically, the change rates of piezoelectric coefficient and inverse piezoelectric coefficient are small within a wide temperature range.

[0010] The purpose of the present application can be realized by the following technical solutions:

[0011] One of the technical solutions of the present application is to provide a potassium sodium niobate-based textured piezoelectric ceramic with high Curie temperature and temperature stability, which has a chemical general formula of (0.99-x)((K 0.5 Na 0.5 )(Nb 0.98 Ta 0.02 )O3)-0.01(Bi(Ni 0.67 Nb 0.33 )O3)-x(Bi 0.5 K 0.5 )HfO3+3wt.%(relative to the mass of the whole powder)NaNbO3, 0≤x≤0.04.

[0012] As a preferred technical solution, the x is 0, 0.01, 0.02, 0.03 or 0.04.

[0013] As a preferred technical solution, the x is 0.03 or 0.04.

[0014] As a preferred technical solution, the x is 0.03.

[0015] Further, when the x is 0.03, the <001> C direction has a higher texture degree (f=97.5%>95%) and exhibits a single tetragonal phase. The grain size is about 20-30 μm, the dielectric constant remains stable from room temperature to the Curie temperature interval, and has a higher Curie temperature (365℃), has a better piezoelectric characteristic, the piezoelectric coefficient d 33 is 331 pC / N, the inverse piezoelectric coefficient is 561 pm / V under an electric field of 20 kV / cm, the piezoelectric coefficient remains stable first and then decreases with the increase of temperature, the piezoelectric coefficient in the temperature range of 25-100℃ and 25-200℃ changes by less than 2% and 10% respectively, showing excellent temperature stability, the unipolar strain remains stable first and then decreases with the increase of temperature, and the corresponding inverse piezoelectric coefficient in the temperature range of 25-175℃ changes by 4.2%, showing excellent temperature stability.

[0016] As a preferred technical solution, the texture degree of the textured ceramic in the <001> C direction is greater than 95%.

[0017] One of the technical solutions of the present application is to provide a preparation method of a potassium sodium niobate-based textured piezoelectric ceramic with high Curie temperature and temperature stability, which comprises the following steps:

[0018] (1) Solid phase synthesis method: select Na2CO3, K2CO3, Nb2O5, Ta2O5, Bi2O3, NiO and HfO2, according to the chemical composition, add ball mill medium for ball milling, discharge and dry to obtain powder base material;

[0019] (2) Two-step molten salt method combined with separation method: first, Bi2O3, K2CO3 and Nb2O5 and molten salt (NaCl) are used for synthesis, separation and filtration to obtain flaky precursor (Bi 2.5 Na 3.5 Nb5O 18 ), and then the flaky precursor and molten salt are used for synthesis, separation and filtration to obtain high-quality pure sodium niobate (NaNbO3) flaky template;

[0020] (3) Template grain growth method: the powder base material obtained in step (1) and the flaky template obtained in step (2) are added into a mixed solvent, a dispersing agent, a plasticizer and a binder, and mixed by using a roll mill to obtain a flowable slurry;

[0021] (4) Flow casting process: the flowable slurry obtained in step (3) is flow cast by using a convenient small-sized coating machine, and then dried to form a dry thick film with certain toughness and plasticity;

[0022] (5) Hot pressing process: the dry thick film obtained in step (4) is cut into a desired shape and stacked layer by layer, and finally hot pressed to form a ceramic green body;

[0023] (6) Glue removal process: the ceramic green body obtained in step (5) is placed in a muffle furnace for glue removal to obtain a ceramic body;

[0024] (7) Two-step sintering process: the ceramic body obtained in step (6) is subjected to two-step sintering, and after naturally cooling to room temperature, sandpaper is used for grinding and polishing to obtain a ceramic sheet;

[0025] (8) Silver firing process: the ceramic sheet obtained in step (7) is coated with silver paste and placed in a muffle furnace for silver firing to obtain a ceramic coated with silver electrodes, and then subjected to electrical testing;

[0026] (9) Polarization process: the ceramic coated with silver electrodes obtained in step (8) is placed in a silicon oil bath for polarization to obtain a potassium sodium niobate-based textured piezoelectric ceramic with temperature stability.

[0027] As a preferred technical scheme, the chemical general formula is (0.99-x)((K 0.5 Na 0.5 )(Nb 0.98 Ta 0.02 )O3)-0.01(Bi(Ni 0.67 Nb0.33 )O3)-x(Bi 0.5 K 0.5 )HfO3 is prepared by solid phase synthesis, the latter half (3wt.% NaNbO3) is prepared by two-step molten salt method and achieved by flaky template combining with separation method.

[0028] Further, the purity of sodium carbonate, potassium carbonate, niobium oxide, tantalum oxide, bismuth oxide, nickel oxide and hafnium oxide is greater than 99.5%.

[0029] Further, the ball milling medium in step (1) is ethanol, and the time is 18-24h.

[0030] Further, the molten salt in step (2) is sodium chloride (NaCl), the total mass ratio of raw material and molten salt is 1:1.1, the holding time is 2h, the molar ratio of bismuth oxide, potassium carbonate and niobium oxide in the first step is 6.5:7:10, the melting temperature is 1050-1100℃, the molar ratio of flaky precursor and potassium carbonate in the second step is 1:1.75, and the melting temperature is 970-990℃.

[0031] The separation reagent is sodium tripolyphosphate, the amount of separation reagent added is 8-10wt.%, the stirring speed is 600-800rpm, and the time is 5-10min.

[0032] As a preferred technical solution, the aspect ratio of the flaky template in step (2) is (10-15):1.

[0033] Further, the mixed solvent in step (3) is butanone and ethanol, the dispersant is glycerol trioleate, the plasticizer is polyethylene glycol and dibutyl phthalate, the binder is polyvinyl butyral (PVB), and the mass ratio of powder base material, flaky template and each reagent (butanone, ethanol, glycerol trioleate, polyethylene glycol, dibutyl phthalate and polyvinyl butyral) is 8.4:0.3:(8-10):(4-6):(0.3-0.35):(0.4-0.5):(0.35-0.5):(1.1-1.3), the mixing speed is 16-18r / min, and the time is 5-8h.

[0034] Further, the moving rate of the casting doctor blade in step (4) is 28-30cm / min.

[0035] As a preferred technical solution, the thickness of the dry thick film in step (4) is 10-15μm.

[0036] As a preferred technical solution, the hot pressing temperature in step (5) is 45-60℃, the pressure is 10MPa, and the time is 0.25-0.5h.

[0037] Further, the glue removing temperature in step (6) is 550-600 DEG C, and the holding time is 10-12 h.

[0038] Further, in step (7), the first heating rate is 3 DEG C / min, the heating temperature is 1175-1195 DEG C, without holding, the second cooling rate is 10 DEG C / min, the cooling temperature is 1075-1095 DEG C, and the holding time is 8-10 h.

[0039] As a preferred technical solution, in step (8), the sandpaper granularity is 400-2000 mesh, and the polishing thickness is 0.4-0.6 mm.

[0040] Further, in step (8), the silver paste diameter is 4-6 mm, the silver burning temperature is 550-600 DEG C, and the holding time is 30 min.

[0041] Further, in step (9), the polarization electric field is 2-4 kV / mm, and the time is 20-30 min.

[0042] In order to obtain KNN-based piezoelectric ceramic materials with high piezoelectric response and excellent temperature stability, a wide temperature range of multiphase coexistence is constructed by chemical doping. (Bi 0.5 K 0.5 )HfO3 is doped into 0.98((K 0.5 Na 0.5 )(Nb 0.98 Ta 0.02 )O3)-0.01(Bi(Ni 0.67 Nb 0.33 )O3) matrix, and the ferroelectric phase transition temperature T O-T is successfully adjusted to room temperature and below, and the Curie temperature does not decrease significantly. The reason for choosing this basic system is that, on the one hand, the electronegativity and ionic radius of Ta element are very close to that of Nb element, and the Nb 5+ at b site of KNN-based ceramic will be preferentially replaced. Due to the difference in melting point between Ta2O5 (1800 DEG C) and Nb2O5 (1460 DEG C), KNN-based ceramics containing Ta need higher sintering temperature, which makes the grain growth of KNN-based ceramics more perfect, which is beneficial to piezoelectric performance. On the other hand, the basic system has a Curie temperature as high as nearly 400 DEG C according to the report, which provides a basis for the high Curie temperature of this work. At the same time, the <001> CThe oriented piezoelectric ceramic improves the piezoelectric performance to a certain extent, and meanwhile reduces the influence of temperature stability reduction caused by temperature-induced phase transition. Therefore, the application can improve the temperature stability while improving the piezoelectric performance and ensuring the Curie temperature. The application provides a good design idea for developing practical advanced functional materials, and is a major breakthrough for realizing the future application of KNN-based piezoelectric ceramics in medium and high temperature environments.

[0043] Compared with the prior art, the application has the following advantages:

[0044] (1) The lead-free textured piezoelectric ceramic with high Curie temperature (365℃) and high piezoelectric performance (piezoelectric coefficient ~ 331pC / N, inverse piezoelectric coefficient ~ 561pm / V) can be obtained by the solid phase synthesis method, the template grain growth method, the casting process and the two-step sintering process. More importantly, the piezoelectric ceramic shows a single tetragonal phase, which is beneficial to temperature stability. Specifically, the change rates of small signal piezoelectric coefficients in the temperature ranges of 25-100℃ and 25-200℃ are less than 2% and 10% respectively, and the change rate of large signal inverse piezoelectric coefficient in the temperature range of 25-175℃ is 4.2%, that is, the inverse piezoelectric coefficient can still be maintained at 538pm / V at 175℃. It is of great significance for developing high-temperature and high-piezoelectricity lead-free piezoelectric materials, and has high application value in the fields of low-temperature and medium-temperature transducers, sensors, drivers and electric actuators.

[0045] (2) The preparation method of the application is simple, economical and practical, and belongs to lead-free materials. In the preparation, application and waste processes, the environment will not be polluted, and it is an environment-friendly high-performance piezoelectric material. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 X-ray diffraction (XRD) patterns of the piezoelectric ceramics in Examples 1 to 5 of the application;

[0047] Figure 2 Scanning electron microscope (SEM) patterns of the potassium sodium niobate-based textured piezoelectric ceramic with high Curie temperature and temperature stability in Example 4 of the application;

[0048] Figure 3 Dielectric temperature spectrum patterns of the piezoelectric ceramics in Examples 1 to 5 of the application;

[0049] Figure 4 Electric hysteresis loop patterns of the piezoelectric ceramics in Examples 1 to 5 of the application;

[0050] Figure 5 In-situ temperature-dependent piezoelectric coefficient patterns of the piezoelectric ceramics in Examples 1 to 5 of the application;

[0051] Figure 6The unipolar strain graph of the sodium potassium niobate-based textured piezoelectric ceramic with high Curie temperature and temperature stability in Example 4 of the present application at different temperatures;

[0052] Figure 7 The inverse piezoelectric coefficient graph of the sodium potassium niobate-based textured piezoelectric ceramic with high Curie temperature and temperature stability in Example 4 of the present application at different temperatures.

[0053] Figure 8 The piezoelectric coefficient and Curie temperature statistical graph of the piezoelectric ceramic in Examples 1 to 5 of the present application. DETAILED DESCRIPTION

[0054] The present application will be described in detail below with specific examples. The present application is implemented on the premise of the technical solution of the present application, and detailed implementation and specific operation processes are given, but the protection scope of the present application is not limited to the following examples.

[0055] The equipment used in the following examples is conventional in the art unless otherwise specified; the reagents used are commercially available or prepared by conventional methods in the art unless otherwise specified, and those not described in detail in the following examples can be achieved by conventional experimental means in the art.

[0056] Sodium carbonate (Na2CO3), potassium carbonate (K2CO3), niobium oxide (Nb2O5), tantalum oxide (Ta2O5), bismuth oxide (Bi2O3), nickel oxide (NiO) and hafnium oxide (HfO2), except bismuth oxide and hafnium oxide from Alpha Chemical Reagent Co., Ltd., the rest from Aladdin Chemical Reagent Co., Ltd., and the purity is greater than 99.5%. Butanone, ethanol, glycerol trioleate, polyethylene glycol, dibutyl phthalate and polyvinyl butyral, except polyvinyl butyral from Aladdin Chemical Reagent Co., Ltd., molecular weight 90000-120000, the rest from Sinopharm Chemical Reagent Co., Ltd., and all are chemical pure.

[0057] Example 1:

[0058] A sodium potassium niobate-based textured piezoelectric ceramic with high Curie temperature and temperature stability has a chemical composition of (0.99-x)((K 0.5 Na 0.5 )(Nb 0.98 Ta 0.02 )O3)-0.01(Bi(Ni 0.67 Nb 0.33 )O3)-x(Bi 0.5 K 0.5 )HfO3+3wt.%NaNbO3, 0≤x≤0.04, wherein x=0, and the preparation method comprises the following specific steps:

[0059] (1) Select 4.4009 g Na2CO3, 21.7073 g Nb2O5, 5.7974 g K2CO3, 0.5923 g Bi2O3, 0.7339 g Ta2O5, 0.0848 g NiO and 0.3567 g HfO2 as the raw materials of the textured piezoelectric ceramic material, weigh according to the chemical composition, add ethanol and ball mill for 24 h, discharge, dry to obtain a powder base;

[0060] (2) By traditional two-step molten salt method and combined with separation method, first, 10 g Bi2O3, 3.1942 g K2CO3 and 8.7762 g Nb2O5 and 24.1674 g NaCl are used for synthesis, melted at 1100℃ for 2h, 10wt% sodium tripolyphosphate is added at 600rpm for 8min, filtered to obtain flaky precursor Bi 2.5 Na 3.5 Nb5O 18 , second, 8g flaky precursor and 1.3705g K2CO3 and 10.3076g NaCl are used for synthesis, melted at 970℃ for 2h, 10wt% sodium tripolyphosphate is added at 600rpm for 8min, filtered to obtain high-quality pure sodium niobate (NaNbO3) flaky template with an aspect ratio of 15:1;

[0061] (3) 8.4g powder base obtained in step (1) and 0.252g flaky template obtained in step (2) are added into 8.8g butanone and 4.4g ethanol (as mixed solvent), 0.32g glyceryl trioleate (as dispersant), 0.4g polyethylene glycol and 0.35g dibutyl phthalate (as plasticizer), 1.15g polyvinyl butyral (PVB) (as binder), mixed in a roll mill at 16r / min for 6h to obtain a casting slurry;

[0062] (4) The casting slurry obtained in step (3) is cast by a convenient small-sized coating machine, the moving speed of the doctor blade is 29cm / min, and then dried to form a dry thick film with certain toughness and plasticity, the thickness is 13μm;

[0063] (5) The dry thick film obtained in step (4) is cut into the required shape and stacked layer by layer, and finally a ceramic green body is formed by hot pressing at 55℃ and 10MPa for 0.25h;

[0064] (6) The ceramic green body obtained in step (5) is placed in a muffle furnace for degassing, and heat treated at 600℃ for 10h to obtain a ceramic body;

[0065] (7) Two-step sintering of the ceramic green body obtained in step (6) was performed by increasing the temperature to 1190°C at a rate of 3°C / min, without holding, then decreasing the temperature to 1090°C at a rate of 10°C / min, holding for 8h, and naturally cooling to room temperature, and then polishing to a thickness of 0.5mm using 800-mesh sandpaper to obtain a ceramic sheet;

[0066] (8) Silver firing process: the ceramic sheet obtained in step (7) was coated with silver paste having a diameter of 4mm, and silver firing was performed in a muffle furnace at 550°C for 30min to obtain a ceramic coated with a silver electrode, and then electrical testing was performed;

[0067] (9) Polarization process: the ceramic coated with a silver electrode obtained in step (8) was placed in a silicon oil bath and polarized at an electric field of 4kV / mm for 30min to obtain a high-voltage potassium sodium niobate-based lead-free textured piezoelectric ceramic having high Curie temperature and excellent temperature stability.

[0068] Example 2:

[0069] A potassium sodium niobate-based textured piezoelectric ceramic having high Curie temperature and temperature stability had a chemical composition of (0.99-x)((K 0.5 Na 0.5 )(Nb 0.98 Ta 0.02 )O3)-0.01(Bi(Ni 0.67 Nb 0.33 )O3)-x(Bi 0.5 K 0.5 )HfO3+3wt.%NaNbO3, 0≤x≤0.04, wherein x=0.01, and the preparation method was substantially the same as in Example 1, except that in step (1), 4.4009g Na2CO3, 21.7073g Nb2O5, 5.7973g K2CO3, 0.5923g Bi2O3, 0.7339g Ta2O5, 0.0848g NiO, and 0.3567g HfO2 were selected as the raw materials for the textured piezoelectric ceramic material, and in step (7), the temperature was increased to 1180°C at a rate of 3°C / min, without holding, then decreased to 1080°C at a rate of 10°C / min, and held for 10h.

[0070] Example 3:

[0071] A potassium sodium niobate-based textured piezoelectric ceramic having high Curie temperature and temperature stability had a chemical composition of (0.99-x)((K 0.5 Na 0.5 )(Nb 0.98 Ta 0.02 )O3)-0.01(Bi(Ni 0.67 Nb 0.33 )O3)-x(Bi0.5 K 0.5 )HfO3+4wt.%NaNbO3, 0 < x < 0.04, where x = 0.02, the method of preparation is substantially the same as Example 1, except that in step (1) 4.3130 g Na2CO3, 21.2740 g Nb2O5, 5.7399 g K2CO3, 0.7819 g Bi2O3, 0.7193 g Ta2O5, 0.0839 g NiO, and 0.7064 g HfO2are selected as the raw materials for the textured piezoelectric ceramic material, and in step (7) the temperature is increased to 1170 °C at a rate of 3 °C / min, without holding, and then decreased to 1070 °C at a rate of 10 °C / min, with holding for 6 h.

[0072] Example 4:

[0073] A textured piezoelectric ceramic based on potassium sodium niobate with high Curie temperature and temperature stability has the chemical composition (0.99-x)((K 0.5 Na 0.5 )(Nb 0.98 Ta 0.02 )O3)-0.01(Bi(Ni 0.67 Nb 0.33 )O3)-x(Bi 0.5 K 0.5 )HfO3+3wt.%NaNbO3, 0 < x < 0.04, where x = 0.03, the method of preparation is substantially the same as Example 1, except that in step (1) 4.2267 g Na2CO3, 20.8493 g Nb2O5, 5.6837 g K2CO3, 0.9678 g Bi2O3, 0.7049 g Ta2O5, 0.0832 g NiO, and 1.0493 g HfO2are selected as the raw materials for the textured piezoelectric ceramic material, and in step (7) the temperature is increased to 1180 °C at a rate of 3 °C / min, without holding, and then decreased to 1080 °C at a rate of 10 °C / min, with holding for 10 h.

[0074] Example 5:

[0075] A textured piezoelectric ceramic based on potassium sodium niobate with high Curie temperature and temperature stability has the chemical composition (0.99-x)((K 0.5 Na 0.5 )(Nb 0.98 Ta 0.02 )O3)-0.01(Bi(Ni 0.67 Nb 0.33 )O3)-x(Bi 0.5 K 0.5)HfO3+3wt. % NaNbO3, 0≤x≤0.04, where x=0.04, the preparation method is substantially the same as example 1, except that in step (1) 4.1421 g Na2CO3, 20.4328 g Nb2O5, 5.6286 g K2CO3, 1.1501 g Bi2O3, 0.6908 g Ta2O5, 0.0823 g NiO and 1.3854 g HfO2 are selected as raw materials of the textured piezoelectric ceramic material, and in step (7) the temperature is raised to 1180 °C at a rate of 3 °C / min, without holding, and then decreased to 1080 °C at a rate of 10 °C / min, with holding for 8 h, each component has a corresponding optimal sintering temperature and holding time, and the mapping data are tested based on the optimal sintering samples of each component.

[0076] As shown in Figure 1 , the texture degrees of examples 1 to 5 are calculated by using the Lotgering factor f, example 1 has a very high texture degree (f=98.3%>95%) in the <001> C direction, example 2 has a very high texture degree (f=98.1%>95%) in the <001> C direction, example 3 has a very high texture degree (f=97.3%>95%) in the <001> C direction, example 4 has a higher texture degree (f=97.5%>95%) in the <001> C direction, and example 5 has a higher texture degree (f=97.3%>95%) in the <001> C direction, and according to the ratio of the peak heights of (002) and (200), the phase structure of the ceramic can be judged, and according to Figure 1 , it can be concluded that example 1 is a single orthorhombic phase, examples 2 and 3 are coexisting orthorhombic-tetragonal phases, and examples 4 and 5 are single tetragonal phases.

[0077] As shown in Figure 2 , the free surface of the ceramic in example 4 is observed, and it can be seen that the grain orientation growth is achieved after the addition of the flaky template, and the grain size is about 20-30 μm.

[0078] As shown in Figure 3 , the phase transition temperature peaks of examples 1, 2 and 3 are all relatively obvious, and as a result, the temperature stability as shown in Figure 5 is also not ideal, but the dielectric constant of examples 4 and 5 remains stable in the temperature range from room temperature to Curie temperature, but example 4 has a higher Curie temperature (365 °C), in addition, example 4 presents a more saturated electric hysteresis loop relative to example 5, and therefore has better piezoelectric properties, with a piezoelectric coefficient d 33 of 331 pC / N and a converse piezoelectric coefficient of 561 pm / V. Therefore, example 4 is selected for other tests.

[0079] like Figure 5 As shown, the piezoelectric coefficient of Example 4 first remains stable and then decreases as the temperature increases. Its piezoelectric coefficient changes by less than 2% and 10% in the temperature ranges of 25-100℃ and 25-200℃, respectively, demonstrating excellent temperature stability.

[0080] Given the stability of the piezoelectric coefficient mentioned above, a curve showing the inverse piezoelectric coefficient versus temperature in Example 4 has been added, as shown below. Figure 6 As shown in Figure 7, the unipolar strain of Example 4 first remained stable and then decreased with increasing temperature. Correspondingly, the inverse piezoelectric coefficient at room temperature can be calculated to be 561 pm / V, which shows a high inverse piezoelectric coefficient. The rate of change in the temperature range of 25-175℃ is also 4.2%, which shows excellent temperature stability.

[0081] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A potassium sodium niobate-based textured piezoelectric ceramic having a high Curie temperature and temperature stability, characterized by, The textured piezoelectric ceramic has a general chemical formula of (0.99-x)((K 0.5 Na 0.5 ) (Nb 0.98 Ta 0.02 )O3)-0.01(Bi(Ni 0.67 Nb 0.33 )O3)-x(Bi 0.5 K 0.5 )HfO3+3wt.%NaNbO3, 0 The preparation method of the textured piezoelectric ceramic comprises the following steps: (1) solid phase synthesis method: select sodium carbonate, potassium carbonate, niobium oxide, tantalum oxide, bismuth oxide, nickel oxide and hafnium oxide, weigh according to the chemical composition, ball mill to obtain powder base material; (2) two-step molten salt method combined with separation method: first, bismuth oxide, potassium carbonate and niobium oxide are synthesized with molten salt, separated and filtered to obtain flaky precursor, and then the flaky precursor and potassium carbonate are synthesized with molten salt, separated and filtered to obtain sodium niobate flaky template; (3) template grain growth method: the powder base material obtained in step (1) and the sodium niobate flaky template obtained in step (2) are added into mixed solvent, dispersant, plasticizer and binder for mixing to obtain casting slurry; (4) casting process: the casting slurry obtained in step (3) is cast, and then dried to form a dry thick film; (5) hot pressing process: the dry thick film obtained in step (4) is stacked layer by layer, and finally hot pressed to form a ceramic green body; (6) glue removal process: the ceramic green body obtained in step (5) is subjected to glue removal to obtain a ceramic body; (7) two-step sintering process: the ceramic body obtained in step (6) is subjected to two-step sintering, and then naturally cooled to room temperature to obtain a ceramic sheet; (8) silver firing process: the ceramic sheet obtained in step (7) is polished with sandpaper of different particle sizes to obtain a thin ceramic sheet with smooth and bright surface, and silver paste is coated on the surface for silver firing to obtain a ceramic coated with silver electrode; (9) polarization process: the ceramic coated with silver electrode obtained in step (8) is polarized to obtain a potassium sodium niobate-based textured piezoelectric ceramic with temperature stability.

2. A method for producing a potassium sodium niobate-based textured piezoelectric ceramic having a high Curie temperature and temperature stability according to claim 1, characterized by, The method comprises the following steps: (1) solid phase synthesis method: select sodium carbonate, potassium carbonate, niobium oxide, tantalum oxide, bismuth oxide, nickel oxide and hafnium oxide, weigh according to the chemical composition, ball mill to obtain powder base material; (2) two-step molten salt method combined with separation method: first, bismuth oxide, potassium carbonate and niobium oxide are synthesized with molten salt, separated and filtered to obtain flaky precursor, and then the flaky precursor and potassium carbonate are synthesized with molten salt, separated and filtered to obtain sodium niobate flaky template; (3) template grain growth method: the powder base material obtained in step (1) and the sodium niobate flaky template obtained in step (2) are added into mixed solvent, dispersant, plasticizer and binder for mixing to obtain casting slurry; (4) casting process: the casting slurry obtained in step (3) is cast, and then dried to form a dry thick film; (5) hot pressing process: the dry thick film obtained in step (4) is stacked layer by layer, and finally hot pressed to form a ceramic green body; (6) glue removal process: the ceramic green body obtained in step (5) is subjected to glue removal to obtain a ceramic body; (7) two-step sintering process: the ceramic body obtained in step (6) is subjected to two-step sintering, and then naturally cooled to room temperature to obtain a ceramic sheet; (8) silver firing process: the ceramic sheet obtained in step (7) is polished with sandpaper of different particle sizes to obtain a thin ceramic sheet with smooth and bright surface, and silver paste is coated on the surface for silver firing to obtain a ceramic coated with silver electrode; (9) polarization process: the ceramic coated with silver electrode obtained in step (8) is polarized to obtain a potassium sodium niobate-based textured piezoelectric ceramic with temperature stability. (9) Polarization process: the silver electrode coated ceramic obtained in step (8) is polarized to obtain a potassium sodium niobate based textured piezoelectric ceramic with temperature stability.

3. The method of claim 2, wherein the method is characterized by the steps of: preparing a precursor powder of the potassium sodium niobate-based textured piezoelectric ceramic; and sintering the precursor powder to form the potassium sodium niobate-based textured piezoelectric ceramic. In step (1), the ball milling medium is ethanol, and the time is 18-24 h.

4. The method of claim 2, wherein the method is characterized by the steps of: preparing a precursor powder of the potassium sodium niobate-based textured piezoelectric ceramic; and sintering the precursor powder to form the potassium sodium niobate-based textured piezoelectric ceramic. In step (2), the molten salt is sodium chloride, the total mass ratio of raw material to molten salt is 1:1.1, the holding time is 2 h, the molar ratio of bismuth oxide, potassium carbonate and niobium oxide in the first step is 6.5:7:10, the melting temperature is 1050-1100 ℃, the molar ratio of flaky precursor to potassium carbonate in the second step is 1:1.75, and the melting temperature is 970-990 ℃. Separation reagents are used for separation, and the separation reagents are all sodium tripolyphosphate, the separation reagent addition amount is 8-10wt.%, the stirring speed is 600-800 rpm, and the time is 5-10 min.

5. The method of claim 2, wherein the method is characterized by the following steps of: (a) mixing the raw materials; (b) calcining the mixture; (c) mixing the calcined mixture; (d) forming the mixture into a green sheet; (e) sintering the green sheet; (f) annealing the sintered green sheet; and (g) polishing the sintered green sheet. In step (3), the mixed solvent is butanone and ethanol, the dispersing agent is glycerol trioleate, the plasticizer is polyethylene glycol and dibutyl phthalate, the binder is polyvinyl butyral, and the mass ratio of powder base material, flaky template, butanone, ethanol, glycerol trioleate, polyethylene glycol, dibutyl phthalate and polyvinyl butyral is 8.4:0.3:(8-10):(4-6):(0.3-0.35):(0.4-0.5):(0.35-0.5):(1.1-1.3), the mixing speed is 16-18 r / min, and the time is 6-8 h.

6. The method of claim 2, wherein the method is characterized by the following steps of: (a) mixing the raw materials; (b) calcining the mixture; (c) mixing the calcined mixture; (d) forming the mixture into a green sheet; (e) sintering the green sheet; (f) annealing the sintered green sheet; and (g) polishing the sintered green sheet. In step (4), the doctor blade moving speed during the casting process is 28-30 cm / min.

7. The method of claim 2, wherein the method is characterized by the following steps of: (a) mixing the starting materials; (b) calcining the mixture; (c) mixing the calcined mixture with the binder; (d) forming the mixture into a green sheet; (e) sintering the green sheet; (f) annealing the sintered green sheet; and (g) polishing the sintered green sheet. In step (6), the glue removal temperature is 550-600 ℃, and the holding time is 10-12 h.

8. The method of claim 2, wherein the method is characterized by the following steps of: (a) mixing the raw materials; (b) calcining the mixture; (c) mixing the calcined mixture; (d) forming the mixture into a green sheet; (e) sintering the green sheet; (f) annealing the sintered green sheet; and (g) polishing the sintered green sheet. In step (7), the first step heating rate is 3 ℃ / min, the heating temperature is 1175-1195 ℃, and there is no holding time, the second step cooling rate is 10 ℃ / min, the cooling temperature is 1075-1095 ℃, and the holding time is 8-10 h.

9. The method of claim 2, wherein the method is characterized by the following steps of: (a) mixing the raw materials; (b) calcining the mixture; (c) mixing the calcined mixture; (d) forming the mixture into a green sheet; (e) sintering the green sheet; (f) annealing the sintered green sheet; and (g) polishing the sintered green sheet. In step (8), the silver paste diameter is 4-6 mm, the silver firing temperature is 550-600 ℃, and the holding time is 30 min.

10. The method of claim 2, wherein the method is characterized by the following steps of: (a) mixing the raw materials; (b) calcining the mixture; (c) mixing the calcined mixture; (d) forming the mixture into a green sheet; (e) sintering the green sheet; (f) annealing the sintered green sheet; and (g) polishing the sintered green sheet. In step (9), the polarization treatment is to polarize the silver fired piezoelectric ceramic in a silicon oil bath, the polarization electric field is 2-4 kV / mm, and the time is 20-30 min.

Images