A five-component BF-BT-based lead-free piezoelectric ceramic with high temperature stability and high piezoelectric performance and a preparation method thereof

Abstract

The application discloses a five-element BF-BT-based lead-free piezoelectric ceramic with high-temperature stability and high-voltage electric performance and a preparation method thereof. 0.5 Na 0.5 )TiO3‑0.2(Bi 0.5 K 0.5 )TiO3]‑zBi(Zn 0.5 Ti 0.5 )O3+uMnO2+vLi2CO3, x, y, z, u and v represent molar fractions, 0.30<=x<=0.40, 0

Description

Technical Field

[0001] This invention relates to lead-free piezoelectric ceramics, specifically to a bismuth ferrite-barium titanate-based high-temperature lead-free piezoelectric ceramic applicable in high-temperature fields, and more specifically to a pentagonal BF-BT-based lead-free piezoelectric ceramic with both high-temperature stability and high-voltage piezoelectric performance, and its preparation method. Background Technology

[0002] High-temperature piezoelectric ceramics are the core components of high-temperature piezoelectric vibration sensors, with significant demand in aerospace, nuclear energy, and oil exploration. Their key characteristics include harsh operating conditions, high operating temperatures, and long service life. Pb(Zr,Ti)O3 (PZT) piezoelectric ceramics, which hold a significant market position, are widely used due to their excellent electrical properties and temperature stability. C Typically below 360℃, the piezoelectric coefficient (d) 33 The lead content in PZT ceramics is typically less than 400 pC / N. However, the toxic lead content in PZT ceramics exceeds 60 wt%. When used in large-scale electronic products or during recycling, the excessively high levels of harmful substances pose serious health and ecological problems for humans and the environment. Therefore, the development of lead-free piezoelectric ceramics that combine high voltage response and high operating temperature is urgently needed.

[0003] One of the most significant breakthroughs in BiFeO3-BaTiO3 (BF-BT) ceramics lies in the manipulation of microdomain organization near the quasi-isomorphic phase boundary (MPB) composition using relaxor ferroelectrics. The disordered distribution of complex valence cations in the relaxor components disrupts the long-range order of the ferroelectrics, refining the domains and constructing locally polar nanodomains. The resulting nanodomains and polar nanodomains (PNRs) exhibit faster switching response speeds than microdomains. Simultaneously, the temperature stability of BF-BT-based ceramics is related to the phase structure and complex domain structure, showing a positive correlation between temperature stability and tetragonality; higher tetragonality correlates with higher temperature stability. Existing research indicates that single manipulation techniques, such as doping modification and A / B site substitution, are insufficient to overcome current research bottlenecks. Furthermore, the construction of ternary systems has not yielded significant breakthroughs in the piezoelectric properties and thermal stability of this system. Therefore, further research is needed to broaden research approaches to improve both piezoelectric activity and temperature stability of the ceramics. Summary of the Invention

[0004] In order to solve d 33 -T d The present invention aims to provide a pentagonal BF-BT-based lead-free piezoelectric ceramic with both high-temperature stability and high-voltage electrical properties, and a method for its preparation. Specifically, the present invention relates to a BiFeO3-BaTiO3-(Bi 0.5 Na0.5 TiO3-(Bi) 0.5 K 0.5 TiO3-Bi(Zn) 0.5 Ti 0.5 Lead-free piezoelectric ceramics (BF-BT-BNT-BKT-BZT) and their preparation method are described. A highly disordered (Bi) group with A-site complex cations is introduced into the BF-BT system. 0.5 Na 0.5 TiO3-(Bi) 0.5 K 0.5 TiO3 relaxor ferroelectrics and Bi(Zn) at the B-site isovalent cation 0.5 Ti 0.5 By adding sintering aids, BiFeO3-BaTiO3-based piezoelectric ceramics with high piezoelectric temperature stability and dense sintering were obtained. The piezoelectric ceramics prepared using this invention can achieve a Curie temperature of Ti. C =491.9℃, and the piezoelectric constant d at a real-time depolarization temperature of 395.6℃. 33 It can still maintain a value above 680 pC / N, and this ceramic system is expected to be used in high-temperature applications.

[0005] The technical solution to achieve the objective of this invention is:

[0006] A pentaceous BF-BT-based lead-free piezoelectric ceramic that combines high-temperature stability and high-voltage electrical performance, comprising...

[0007] (1) Select (1-x)BiFeO3-xBaTiO3 with a high Curie temperature and a composition ratio close to that of MPB structure with RT phase coexistence as the matrix material, where 0.30 ≤ x ≤ 0.40;

[0008] (2) Select 0.8 (Bi) near MPB where RT phases coexist. 0.5 Na 0.5 TiO3-0.2(Bi) 0.5 K 0.5 TiO3 is used as a relaxor solid solution to control domain structure and size, utilizing the high tetragonality of Bi(Zn) 0.5 Ti 0.5 O3 can be used to regulate the stability of the ferroelectric phase;

[0009] (3) Design

[0010] (1-y)[(1-x)BiFeO3-xBaTiO3)]-y[0.8(Bi 0.5 Na 0.5 TiO3-0.2(Bi) 0.5 K 0.5 TiO3]-zBi(Zn0.5 Ti 0.5 O3 formulation, constructing a pentagonal system BF-BT-BNT-BKT-BZT.

[0011] Specifically, a pentagonal BF-BT-based lead-free piezoelectric ceramic that combines high-temperature stability and high-voltage electrical performance has the following general formula:

[0012] (1-y)[(1-x)BiFeO3-xBaTiO3)]-y[0.8(Bi 0.5 Na 0.5 TiO3-0.2(Bi) 0.5 K 0.5 TiO3]-zBi(Zn 0.5 Ti 0.5 The reaction is O3 + uMnO2 + vLi2CO3, where x, y, z, u and v represent the mole fractions of the components, and 0.30 ≤ x ≤ 0.40, 0 < y < 0.05, 0 < z ≤ 0.05, 0 < u ≤ 0.01, 0 < v ≤ 0.01.

[0013] The preparation method of the pentagonal BF-BT-based lead-free piezoelectric ceramic with both high-temperature stability and high-voltage electrical properties includes the following steps:

[0014] 1) Using analytical grade Bi₂O₃, TiO₂, Na₂CO₃, and K₂CO₃ as raw materials, according to 0.8 (Bi 0.5 Na 0.5 TiO3-0.2(Bi) 0.5 K 0.5 The TiO3 was prepared according to the specified ratio. The uniformly mixed powder was ball-milled for 24 hours using anhydrous ethanol as the medium. After removal, it was dried in an oven at 80℃ for 12 hours, passed through a 200-mesh sieve, and then placed in a high-alumina crucible, compacted, and covered. It was then placed in a muffle furnace and pre-fired at 800℃ at a heating rate of 2℃ / min for 6 hours. After cooling to below 200℃, it was removed to synthesize 0.8(Bi 0.5 Na 0.5 TiO3-0.2(Bi) 0.5 K 0.5 TiO3 powder is available for use.

[0015] 2) Using analytically pure Bi₂O₃, Fe₂O₃, BaCO₃, TiO₂, ZnO, MnO₂, and Li₂CO₃ as raw materials, and combining the 0.8(Bi₂O₃) synthesized in step 1), 0.5 Na 0.5 TiO3-0.2(Bi) 0.5 K 0.5The pre-calcined TiO3 powder is prepared according to (1-y)[(1-x)BiFeO3-xBaTiO3)]-y[0.8(Bi 0.5 Na 0.5 TiO3-0.2(Bi) 0.5 K 0.5 TiO3]-zBi(Zn 0.5 Ti 0.5 The ingredients were weighed and mixed in the proportion of O3 + uMnO2 + vLi2CO3, where x, y, z, u and v represent the mole fractions of the components, and 0.30 ≤ x ≤ 0.40, 0 < y < 0.05, 0 < z ≤ 0.05, 0 < u ≤ 0.01, 0 < v ≤ 0.01; Bi element was in excess at 4.0% mol. To compensate for the volatilization of bismuth element during sintering, the mixed powder was ball-milled with anhydrous ethanol as the medium for 24 h, then dried in an oven at 80℃ for 12 h, passed through a 200-mesh sieve, placed in a high-alumina crucible, compacted and covered, and then placed in a muffle furnace for pre-firing at 780℃ for 6 h.

[0016] 3) After the pre-calcined powder is fully ground, an 8% concentration of PVA solution is added to granulate it, and then it is pressed into shape in a powder tablet press at a pressure of 12MPa.

[0017] 4) The formed raw sheet is placed in a muffle furnace and slowly heated to 600℃ at a heating rate of 30℃ / h, held for 3h to remove the glue; then heated to 950-1000℃ at a heating rate of 2℃ / min for sintering, held for 240min and then cooled to room temperature in the furnace.

[0018] 5) Grind and polish the sintered ceramic sheet, then coat its sample surface with silver paste and fire it at 450℃ for 30 minutes;

[0019] 6) Polarize the ceramic sheet after it has been coated with silver electrodes in silicone oil. The polarization electric field is 6000V / mm, the polarization temperature is 110℃, and the time is 5-15min. Keep the voltage constant and let the temperature drop to room temperature before taking it out.

[0020] The ceramic pieces were left to stand in air at room temperature for 24 hours after being removed before their performance was measured.

[0021] To improve piezoelectric temperature stability while maintaining a high Curie temperature, this invention selects a device with a T... C Bi(Zn) with a high Curie temperature of 1294℃ and a high tetragonality of c / a = 1.21 0.5 Ti 0.5 O3 (BZT) and (Bi) at room temperature are trigonal phases. 0.5 Na 0.5 TiO3 (BNT) and tetragonal phase (Bi) 0.5 K0.5 High-performance lead-free piezoelectric ceramics with a coexisting RT phase system (BF-BT-BNT-BKT-BZT) were successfully prepared using TiO3 (BKT). By simultaneously controlling the phase structure and domain structure, both temperature stability and piezoelectric properties were improved, resulting in a Curie temperature T0. C >480℃, in-situ depolarization temperature T dr >380℃, maximum operating temperature exceeds 380℃, piezoelectric performance reaches d at temperature T>380℃. 33 High-performance lead-free piezoelectric ceramic with a strength of >680 pC / N.

[0022] The positive effects of this invention are:

[0023] (1) Phase boundary regulation to improve thermal stability: A BF-BT matrix with coexisting RT phases and a BNT-BKT composite relaxor ferroelectric material with coexisting RT phases were selected, both of which are located near the quasi-isomorphic phase boundary MPB. The phase structure of BF-BT-BNT-BKT was regulated by a trace amount of BZT to obtain a BF-BT-BNT-BKT-BZT pentagonal ceramic system with coexisting RT phases and closer to the T phase, thereby improving the thermal stability of the ceramic.

[0024] (2) Enhancing piezoelectric activity through domain structure regulation: Introducing highly disordered (Bi) cations at the A and B sites into the BF-BT system 0.5 Na 0.5 TiO3, (Bi) 0.5 K 0.5 TiO3, Bi(Zn) 0.5 Ti 0.5 O3, utilizing the relaxation properties of BNT, the A-site complex cations of BKT, and the B-site complex cations of BZT, disrupts the long-range order of the ferroelectric domains in BF-BT, refining the domain size and obtaining BF-BT-BNT-BKT-BZT ceramics with a large number of nanodomains and polar nano-microregions. (See appendix) Figure 1 As shown, Figure 1 The Moiré fringes region marked in (a) is a polar nanoregion (PNRs); Figure 1 (b) The numerous fingerprint-like regions are composite domain structures in which wide nanodomains coexist with PNRs.

[0025] (3) High Curie temperature components improve thermal stability: BiFeO3, BaTiO3, (Bi 0.5 Na 0.5 TiO3, (Bi) 0.5 K 0.5 TiO3, Bi(Zn) 0.5 Ti 0.5All O3 molecules have a perovskite structure and can form solid solutions. BiFeO3 and BaTiO3 can form MPB with coexisting RT phases near 0.68BF-0.32BT. C ≈450℃; (Bi 0.5 Na 0.5 TiO3 and (Bi) 0.5 K 0.5 TiO3 can form MPB with coexisting RT phases in the vicinity of 0.82 BNT-0.18 BKT. C ≈320℃; while Bi(Zn 0.5 Ti 0.5 O3 has a high Curie temperature of over 1200℃, and based on this, a pentagonal ceramic system with a high Curie temperature, BF-BT-BNT-BKT-BZT, was constructed.

[0026] (4) Excellent high-temperature piezoelectric properties: Through reasonable composition design and optimized sintering process, the BF-BT-BNT-BKT-BZT ceramic material prepared by this invention has ultra-high piezoelectric temperature stability, and still exhibits high d at a real-time depolarization temperature of 395.6℃. 33 The piezoelectric properties are 749.6 pC / N, see attached figure. Figure 2 As shown, this is suitable for high-temperature applications. Attached Figure Description

[0027] Figure 1 Screenshots of the Moiré fringes region showing polar nanoregions (PNRs) and composite domain structures where nanodomains coexist with PNRs;

[0028] Figure 2 Td of the piezoelectric ceramic of the present invention 33 In-situ depolarization curve. Detailed Implementation

[0029] The present invention will be further illustrated below through embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0030] Example 1:

[0031] A pentaceous BF-BT-based lead-free piezoelectric ceramic exhibiting both high-temperature stability and high-voltage electrical properties has the following chemical formula:

[0032] 0.98(0.7BiFeO3-0.3BaTiO3)-0.02[0.8(Bi 0.5 Na 0.5TiO3-0.2(Bi) 0.5 K 0.5 TiO3]-0.04Bi(Zn 0.5 Ti 0.5 )O3+0.01MnO2+0.01Li2CO3.

[0033] The preparation method includes the following steps:

[0034] (1) Using analytical grade Bi2O3, TiO2, Na2CO3 and K2CO3 as raw materials, according to 0.8 (Bi 0.5 Na 0.5 TiO3-0.2(Bi) 0.5 K 0.5 The TiO3 was prepared according to the specified ratio. The uniformly mixed powder was ball-milled for 24 hours using anhydrous ethanol as the medium. After removal, it was dried in an oven at 80℃ for 12 hours, passed through a 200-mesh sieve, and then placed in a high-alumina crucible, compacted, and covered. It was then placed in a muffle furnace and pre-fired at 800℃ at a heating rate of 2℃ / min for 6 hours. After cooling to below 200℃, it was removed to synthesize 0.8(Bi 0.5 Na 0.5 TiO3-0.2(Bi) 0.5 K 0.5 TiO3 powder is available for use.

[0035] (2) Using analytically pure Bi2O3, Fe2O3, BaCO3, TiO2, MnO2, Li2CO3 and ZnO as raw materials, and the 0.8(Bi2O3) synthesized in step (1) is used as the raw material. 0.5 Na 0.5 TiO3-0.2(Bi) 0.5 K 0.5 TiO3 pre-calcined powder according to

[0036] 0.98(0.7BiFeO3-0.3BaTiO3)-0.02[0.8(Bi 0.5 Na 0.5 TiO3-0.2(Bi) 0.5 K 0.5 TiO3]-0.04Bi(Zn 0.5 Ti 0.5 Weigh and mix the ingredients in the ratio of O3 + 0.01MnO2 + 0.01Li2CO3, with Bi element in excess at 4.0%mol. To compensate for the volatilization of Bi element during sintering, the mixed powder is ball-milled with anhydrous ethanol as the medium for 24 hours, then dried in an oven at 80℃ for 12 hours, passed through a 200-mesh sieve, placed in a high-alumina crucible, compacted and covered, and then placed in a muffle furnace for pre-firing at 780℃ for 6 hours.

[0037] (3) After the pre-calcined powder is fully ground, an 8% concentration of PVA solution is added to granulate it, and then it is pressed into shape in a powder tablet press at a pressure of 12MPa.

[0038] (4) The formed sheet is placed in a muffle furnace and slowly heated to 600°C at a heating rate of 30°C / h, and held for 3h to remove the glue; then it is heated to 1000°C at a heating rate of 2°C / min for sintering, and held for 240min before being cooled to room temperature in the furnace.

[0039] (5) Polish the sintered ceramic sheet, then coat the sample surface with silver paste and burn it at 450℃ for 30 minutes;

[0040] (6) Polarize the ceramic sheet after it is coated with silver electrodes in silicone oil. The polarization electric field is 6000V / mm, the polarization temperature is 110℃, and the time is 5-15min. Keep the voltage constant and then take it out when the temperature drops to room temperature.

[0041] The ceramic pieces were left to stand in air at room temperature for 24 hours after being removed before their performance was measured.

[0042] The performance measurement results are as follows:

[0043] .

[0044] Example 2:

[0045] A pentaceous BF-BT-based lead-free piezoelectric ceramic exhibiting both high-temperature stability and high-voltage electrical properties has the following chemical formula:

[0046] 0.98(0.68BiFeO3-0.32BaTiO3)-0.02[0.8(Bi 0.5 Na 0.5 TiO3-0.2(Bi) 0.5 K 0.5 TiO3]-0.04Bi(Zn 0.5 Ti 0.5 )O3+0.01MnO2+0.01Li2CO3.

[0047] The preparation method is the same as in Example 1, except that:

[0048] In step (2) according to

[0049] 0.98(0.68BiFeO3-0.32BaTiO3)-0.02[0.8(Bi 0.5 Na 0.5 TiO3-0.2(Bi) 0.5 K 0.5 TiO3]-0.04Bi(Zn 0.5 Ti 0.5The ingredients are prepared by mixing O3, 0.01MnO2, and 0.01Li2CO3.

[0050] The performance measurement results are as follows:

[0051] .

[0052] Example 3:

[0053] A pentaceous BF-BT-based lead-free piezoelectric ceramic exhibiting both high-temperature stability and high-voltage electrical properties has the following chemical formula:

[0054] 0.98(0.67BiFeO3-0.33BaTiO3)-0.02[0.8(Bi 0.5 Na 0.5 TiO3-0.2(Bi) 0.5 K 0.5 TiO3]-0.04Bi(Zn 0.5 Ti 0.5 )O3+0.01MnO2+0.01Li2CO3.

[0055] The preparation method is the same as in Example 1, except that:

[0056] In step (2) according to

[0057] 0.98(0.67BiFeO3-0.33BaTiO3)-0.02[0.8(Bi 0.5 Na 0.5 TiO3-0.2(Bi) 0.5 K 0.5 TiO3]-0.04Bi(Zn 0.5 Ti 0.5 The ingredients are prepared by mixing O3, 0.01MnO2, and 0.01Li2CO3.

[0058] The performance measurement results are as follows:

[0059] .

[0060] Example 4:

[0061] A pentaceous BF-BT-based lead-free piezoelectric ceramic exhibiting both high-temperature stability and high-voltage electrical properties has the following chemical formula:

[0062] 0.97(0.68BiFeO3-0.32BaTiO3)-0.03[0.8(Bi 0.5 Na 0.5 TiO3-0.2(Bi) 0.5 K 0.5 TiO3]-0.04Bi(Zn0.5 Ti 0.5 )O3+0.01MnO2+0.01Li2CO3.

[0063] The preparation method is the same as in Example 1, except that:

[0064] In step (2) according to

[0065] 0.97(0.68BiFeO3-0.32BaTiO3)-0.03[0.8(Bi 0.5 Na 0.5 TiO3-0.2(Bi) 0.5 K 0.5 TiO3]-0.04Bi(Zn 0.5 Ti 0.5 The ingredients are prepared in the ratio of O3 + 0.01MnO2 + 0.01Li2CO3.

[0066] The sintering temperature in step (4) is 960℃.

[0067] The performance measurement results are as follows:

[0068] .

[0069] Example 5:

[0070] A pentaceous BF-BT-based lead-free piezoelectric ceramic exhibiting both high-temperature stability and high-voltage electrical properties has the following chemical formula:

[0071] 0.96(0.68BiFeO3-0.32BaTiO3)-0.04[0.8(Bi 0.5 Na 0.5 TiO3-0.2(Bi) 0.5 K 0.5 TiO3]-0.04Bi(Zn 0.5 Ti 0.5 )O3+0.01MnO2+0.01Li2CO3.

[0072] The preparation method is the same as in Example 1, except that:

[0073] In step (2) according to

[0074] 0.96(0.68BiFeO3-0.32BaTiO3)-0.04[0.8(Bi 0.5 Na 0.5 TiO3-0.2(Bi) 0.5 K 0.5 TiO3]-0.04Bi(Zn 0.5 Ti 0.5The ingredients are prepared in the ratio of O3 + 0.01MnO2 + 0.01Li2CO3.

[0075] The sintering temperature in step (4) is 960℃.

[0076] The performance measurement results are as follows:

[0077] .

[0078] Example 6:

[0079] A pentaceous BF-BT-based lead-free piezoelectric ceramic exhibiting both high-temperature stability and high-voltage electrical properties has the following chemical formula:

[0080] 0.98(0.68BiFeO3-0.32BaTiO3)-0.02[0.8(Bi 0.5 Na 0.5 TiO3-0.2(Bi) 0.5 K 0.5 TiO3]-0.02Bi(Zn 0.5 Ti 0.5 )O3+0.01MnO2+0.01Li2CO3.

[0081] The preparation method is the same as in Example 1, except that:

[0082] In step (2) according to

[0083] 0.98(0.68BiFeO3-0.32BaTiO3)-0.02[0.8(Bi 0.5 Na 0.5 TiO3-0.2(Bi) 0.5 K 0.5 TiO3]-0.02Bi(Zn 0.5 Ti 0.5 The ingredients are prepared in the ratio of O3 + 0.01MnO2 + 0.01Li2CO3.

[0084] The sintering temperature in step (4) is 980℃.

[0085] The performance measurement results are as follows:

[0086] .

[0087] Example 7:

[0088] A pentaceous BF-BT-based lead-free piezoelectric ceramic exhibiting both high-temperature stability and high-voltage electrical properties has the following chemical formula:

[0089] 0.98(0.68BiFeO3-0.32BaTiO3)-0.02[0.8(Bi 0.5 Na 0.5 TiO3-0.2(Bi) 0.5 K 0.5 TiO3]-0.03Bi(Zn 0.5 Ti 0.5 )O3+0.01MnO2+0.01Li2CO3.

[0090] The preparation method is the same as in Example 1, except that:

[0091] In step (2) according to

[0092] 0.98(0.68BiFeO3-0.32BaTiO3)-0.02[0.8(Bi 0.5 Na 0.5 TiO3-0.2(Bi) 0.5 K 0.5 TiO3]-0.03Bi(Zn 0.5 Ti 0.5 The ingredients are prepared in the ratio of O3 + 0.01MnO2 + 0.01Li2CO3.

[0093] The sintering temperature in step (4) is 980℃.

[0094] The performance measurement results are as follows:

[0095] .

[0096] The upper and lower limits and ranges of the components listed in this invention, as well as the upper and lower limits and ranges of the process parameters, can all realize this invention, and will not be listed one by one here.

[0097] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A pentagonal BF-BT-based lead-free piezoelectric ceramic possessing both high-temperature stability and high-voltage electrical properties, characterized in that: The general formula for the composition of the ceramic is: (1- y )[(1- x BiFeO3- x BaTiO3)]- y [0.8(Bi 0.5 Na 0.5 TiO3-0.2(Bi) 0.5 K 0.5 TiO3]- z Bi(Zn 0.5 Ti 0.5 O3+ u MnO2+ v Li2CO3, in which x, y ,z, u、v This represents the mole fraction of the component, and 0.30 ≤ x ≤0.40, 0 < y < 0.05, 0 < z ≤ 0.05, 0 < u ≤ 0.01, 0 < v ≤ 0.

01.

2. The pentagonal BF-BT-based lead-free piezoelectric ceramic with both high-temperature stability and high-voltage electrical properties according to claim 1, wherein the chemical formula of the ceramic is: 0.98(0.7BiFeO3-0.3BaTiO3)-0.02[0.8(Bi 0.5 Na 0.5 )TiO3-0.2(Bi 0.5 K 0.5 [TiO3]-0.04Bi(Zn) 0.5 Ti 0.5 )O3 + 0.01MnO2 + 0.01Li2CO3。 3. The pentagonal BF-BT-based lead-free piezoelectric ceramic with both high-temperature stability and high-voltage electrical properties according to claim 1, wherein the chemical formula of the ceramic is: 0.98(0.68BiFeO3-0.32BaTiO3)-0.02[0.8(Bi 0.5 Na 0.5 )TiO3-0.2(Bi 0.5 K 0.5 [TiO3]-0.04Bi(Zn) 0.5 Ti 0.5 )O3 + 0.01MnO2 + 0.01Li2CO3。 4. The pentagonal BF-BT-based lead-free piezoelectric ceramic with both high-temperature stability and high-voltage electrical properties according to claim 1, wherein the chemical formula of the ceramic is: 0.98(0.67BiFeO3-0.33BaTiO3)-0.02[0.8(Bi 0.5 Na 0.5 )TiO3-0.2(Bi 0.5 K 0.5 [TiO3]-0.04Bi(Zn) 0.5 Ti 0.5 )O3 + 0.01MnO2 + 0.01Li2CO3。 5. The pentagonal BF-BT-based lead-free piezoelectric ceramic with both high-temperature stability and high-voltage electrical properties according to claim 1, wherein the chemical formula of the ceramic is: 0.97(0.68BiFeO3-0.32BaTiO3)-0.03[0.8(Bi 0.5 Na 0.5 )TiO3-0.2(Bi 0.5 K 0.5 [TiO3]-0.04Bi(Zn) 0.5 Ti 0.5 )O3 + 0.01MnO2 + 0.01Li2CO3。 6. The pentagonal BF-BT-based lead-free piezoelectric ceramic with both high-temperature stability and high-voltage electrical properties according to claim 1, wherein the chemical formula of the ceramic is: 0.96(0.68BiFeO3-0.32BaTiO3)-0.04[0.8(Bi 0.5 Na 0.5 )TiO3-0.2(Bi 0.5 K 0.5 [TiO3]-0.04Bi(Zn) 0.5 Ti 0.5 )O3 + 0.01MnO2 + 0.01Li2CO3。 7. The pentagonal BF-BT-based lead-free piezoelectric ceramic with both high-temperature stability and high-voltage electrical properties according to claim 1, wherein the chemical formula of the ceramic is: 0.98(0.68BiFeO3-0.32BaTiO3)-0.02[0.8(Bi 0.5 Na 0.5 )TiO3-0.2(Bi 0.5 K 0.5 [TiO3]-0.02Bi(Zn) 0.5 Ti 0.5 )O3 + 0.01MnO2 + 0.01Li2CO3。 8. The pentagonal BF-BT-based lead-free piezoelectric ceramic with both high-temperature stability and high-voltage electrical properties according to claim 1, wherein the chemical formula of the ceramic is: 0.98(0.68BiFeO3-0.32BaTiO3)-0.02[0.8(Bi 0.5 Na 0.5 )TiO3-0.2(Bi 0.5 K 0.5 [TiO3]-0.03Bi(Zn) 0.5 Ti 0.5 )O3 + 0.01MnO2 + 0.01Li2CO3。 9. The method for preparing the pentagonal BF-BT-based lead-free piezoelectric ceramic with both high-temperature stability and high-voltage electrical properties as described in claim 1, characterized in that, Includes the following steps: 1) Using analytical grade Bi₂O₃, TiO₂, Na₂CO₃, and K₂CO₃ as raw materials, according to 0.8 (Bi 0.5 Na 0.5 TiO3-0.2(Bi) 0.5 K 0.5 The TiO3 was prepared according to the specified ratio. The uniformly mixed powder was ball-milled for 24 hours using anhydrous ethanol as the medium. After removal, it was dried in an oven at 80℃ for 12 hours, passed through a 200-mesh sieve, and then placed in a high-alumina crucible, compacted, and covered. It was then placed in a muffle furnace and pre-fired at 800℃ at a heating rate of 2℃ / min for 6 hours. After cooling to below 200℃, it was removed to synthesize 0.8(Bi 0.5 Na 0.5 TiO3-0.2(Bi) 0.5 K 0.5 TiO3 powder is available for use. 2) Using analytically pure Bi₂O₃, Fe₂O₃, BaCO₃, TiO₂, ZnO, MnO₂, and Li₂CO₃ as raw materials, and combining the 0.8(Bi₂O₃) synthesized in step 1), 0.5 Na 0.5 TiO3-0.2(Bi) 0.5 K 0.5 TiO3 pre-calcined powder according to (1- y )[(1- x BiFeO3- x BaTiO3)]- y [0.8(Bi 0.5 Na 0.5 TiO3-0.2(Bi) 0.5 K 0.5 TiO3]- z Bi(Zn 0.5 Ti 0.5 O3+ u MnO2+ v The proportions of Li2CO3 ingredients were weighed and mixed. x, y , z , u and v This represents the mole fraction of the component, and 0.30 ≤ x ≤ 0.40, 0 < y < 0.05, 0 < z ≤0.05, 0 < u ≤ 0.01, 0 < v ≤ 0.01; The excess of Bi element is 4.0%mol to compensate for the volatilization of Bi element during sintering. The mixed powder is ball-milled with anhydrous ethanol as the medium for 24 hours, then dried in an oven at 80°C for 12 hours, passed through a 200-mesh sieve, placed in a high-alumina crucible, compacted and covered, and then placed in a muffle furnace for pre-firing at 780°C for 6 hours. 3) After the pre-calcined powder is fully ground, an 8% concentration of PVA solution is added to granulate it, and then it is pressed into shape in a powder tablet press at a pressure of 12MPa. 4) The formed raw sheet is placed in a muffle furnace and slowly heated to 600℃ at a heating rate of 30℃ / h, held for 3h to remove the glue; then heated to 950-1000℃ at a heating rate of 2℃ / min for sintering, held for 240min and then cooled to room temperature in the furnace. 5) Grind and polish the sintered ceramic sheet, then coat its sample surface with silver paste and fire it at 450℃ for 30 minutes; 6) Polarize the ceramic sheet after it has been coated with silver electrodes in silicone oil. The polarization electric field is 6000V / mm, the polarization temperature is 110℃, and the time is 5-15min. Keep the voltage constant and let the temperature drop to room temperature before taking it out.

10. The method for preparing the pentagonal BF-BT-based lead-free piezoelectric ceramic with both high-temperature stability and high-voltage electrical properties according to claim 9, characterized in that, Includes the following steps: (1) Using analytical grade Bi2O3, TiO2, Na2CO3 and K2CO3 as raw materials, according to 0.8 (Bi 0.5 Na 0.5 TiO3-0.2(Bi) 0.5 K 0.5 The TiO3 was prepared according to the specified ratio. The uniformly mixed powder was ball-milled for 24 hours using anhydrous ethanol as the medium. After removal, it was dried in an oven at 80℃ for 12 hours, passed through a 200-mesh sieve, and then placed in a high-alumina crucible, compacted, and covered. It was then placed in a muffle furnace and pre-fired at 800℃ at a heating rate of 2℃ / min for 6 hours. After cooling to below 200℃, it was removed to synthesize 0.8(Bi 0.5 Na 0.5 TiO3-0.2(Bi) 0.5 K 0.5 TiO3 powder is available for use. (2) Using analytically pure Bi2O3, Fe2O3, BaCO3, TiO2, MnO2, Li2CO3 and ZnO as raw materials, and the 0.8(Bi2O3) synthesized in step (1) 0.5 Na 0.5 TiO3-0.2(Bi) 0.5 K 0.5 The pre-calcined TiO3 powder was prepared according to the following formula: 0.98 (0.7BiFeO3-0.3BaTiO3)-0.02 [0.8 (BiFeO3-0.3BaTiO3)-0.02]. 0.5 Na 0.5 TiO3-0.2(Bi) 0.5 K 0.5 TiO3]-0.04Bi(Zn 0.5 Ti 0.5 Weigh and mix the ingredients in the ratio of O3 + 0.01MnO2 + 0.01Li2CO3, with Bi element in excess at 4.0%mol. To compensate for the volatilization of Bi element during sintering, the mixed powder is ball-milled with anhydrous ethanol as the medium for 24 hours, then dried in an oven at 80℃ for 12 hours, passed through a 200-mesh sieve, placed in a high-alumina crucible, compacted and covered, and then placed in a muffle furnace for pre-firing at 780℃ for 6 hours. (3) After the pre-calcined powder is fully ground, an 8% concentration of PVA solution is added to granulate it, and then it is pressed into shape in a powder tablet press at a pressure of 12MPa. (4) The formed sheet is placed in a muffle furnace and slowly heated to 600°C at a heating rate of 30°C / h, and held for 3h to remove the glue; then it is heated to 1000°C at a heating rate of 2°C / min for sintering, and held for 240min before being cooled to room temperature in the furnace. (5) Polish the sintered ceramic sheet, then coat the sample surface with silver paste and burn it at 450℃ for 30 minutes; (6) Polarize the ceramic sheet after it is coated with silver electrodes in silicone oil. The polarization electric field is 6000V / mm, the polarization temperature is 110℃, and the time is 5-15min. Keep the voltage constant and let the temperature drop to room temperature before taking it out.

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