Sodium bismuth titanate-based piezoelectric ceramic material and preparation method thereof

Abstract

The invention discloses a sodium bismuth titanate-based piezoelectric ceramic material and a preparation method thereof, and belongs to the technical field of leadless piezoelectric ceramic materials, the sodium bismuth titanate-based piezoelectric ceramic material provides a (1-x-y) BNT + xBKT + yBT (x is more than or equal to 0.10 and less than or equal to 0.18, and y is more than or equal to 0.06 and less than or equal to 0.12) main body system, and is prepared by double doping 0.4-0.9 mol% of La2O3 and 0.2-0.5 mol% of MnO2 (wherein the ratio of La2O3 to Mn is 1.2-2.5: 1), and matching with a Bi2O3 + B2O3 + Li2CO3 reactive composite sintering aid and T1 (980-1040 DEG C) / T2 (880-950 DEG C) through two-step sintering. According to the scheme, high densification at the low temperature of less than or equal to 950-1000 DEG C is realized, tan delta (less than or equal to 1.5% at1kHz) is remarkably reduced, Eb (greater than or equal to 7kV / mm) is improved, and relatively high d33 and good temperature / anti-aging stability are achieved.

Description

Technical Field

[0001] This invention belongs to the technical field of lead-free piezoelectric ceramic materials, specifically relating to a sodium bismuth titanate-based piezoelectric ceramic material and its preparation method. Background Technology

[0002] Sodium bismuth titanate-based piezoelectric ceramics (a solid solution system mainly composed of (Na,Bi)TiO3) have attracted widespread attention and are used in lead-free actuators, ultrasonic transducers, micro-pump drives, energy harvesting, and precision positioning devices due to their lead-free nature, high piezoelectric response, and good heat resistance. These applications often require materials to operate under medium to high electric fields for extended periods and maintain stable piezoelectric output and low losses over a wide temperature range, thereby improving device efficiency and reliability.

[0003] Existing BNT-based ceramics generally face the following contradictions in engineering applications: to obtain higher d33 and lower driving voltage, it is often necessary to introduce morphology phase boundary / relaxation phase regulation or heterovalent doping; however, these methods often lead to problems such as narrowing of the sintering window, difficulty in densification, increased dielectric loss, decreased breakdown strength, poorer temperature stability, or accelerated performance degradation (aging) after polarization. Especially in low-temperature co-firing / silver electrode co-firing (≤950℃) or thick film / multilayer structures, traditional BNT-based systems often require higher sintering temperatures (usually >1100℃) to achieve sufficient densification, resulting in electrode diffusion, warpage cracking, and increased performance dispersion.

[0004] With increasingly stringent lead-free regulations and growing demand for multilayer piezoelectric devices, miniaturization, and low-cost manufacturing, the industry urgently needs a BNT-based material system and preparation method that can achieve high density at lower sintering temperatures while maintaining high voltage performance, low dielectric loss, high breakdown strength, and good temperature / aging stability. Failure to systematically resolve the coupling contradiction between "low-temperature densification - low loss - high reliability" at the material level will severely limit the large-scale application of BNT-based lead-free piezoelectric ceramics in high-reliability actuation, energy harvesting, and multilayer devices. Summary of the Invention

[0005] The purpose of this invention is to provide a bismuth sodium titanate-based piezoelectric ceramic material and its preparation method to solve the technical problems of existing BNT-based piezoelectric ceramics: (1) high sintering temperature and difficulty in densification at low temperature; (2) high dielectric loss and insufficient breakdown strength; (3) rapid performance decay after polarization and poor temperature stability; (4) narrow process window and poor batch consistency.

[0006] The objective of this invention can be achieved through the following technical solutions: To achieve the above objectives, the present invention provides a bismuth sodium titanate-based piezoelectric ceramic material, characterized by employing a synergistic scheme of "main body solid solution phase boundary regulation + controlled defect chemistry (dual doping) + reactive composite sintering aid (in-situ liquid phase-re-solidification) + two-step sintering (suppressing abnormal grains)", which enables the material to achieve high density in the temperature range of ≤950~1000℃, and significantly reduces tanδ and improves breakdown strength and temperature stability while maintaining a high d33.

[0007] (1) The main components (in mole fraction) are: (1-xy)BNT+xBKT+yBT; in: BNT=(Bi 0.5 Na 0.5 TiO3; BKT=(Bi 0.5 K 0.5 TiO3; BT = BaTiO3; And it satisfies: 0.10≤x≤0.18, 0.06≤y≤0.12.

[0008] This region is used to form controllable relaxation / phase boundary characteristics to obtain high response and polarizability.

[0009] 2) A-site controlled defect doping: 0.4–0.9 mol% La₂O₃ (based on ABO₃) is introduced for A-site donor doping to suppress oxygen vacancy-related conductivity and aging; simultaneously, 0.2–0.5 mol% MnO₂ is introduced for acceptor doping, forming a “suitable defect dipole” to improve polarization stability, reduce losses, and increase breakdown strength. The combination range of La and Mn satisfies: La: 0.4–0.9 mol% Mn: 0.2–0.5 mol% Furthermore, the La:Mn molar ratio is preferably in the range of (1.2 to 2.5):1.

[0010] Unexpected effect: Unlike single La or single Mn, the synergy of the two can simultaneously achieve "low tanδ + high Eb + low aging" under low-temperature densification conditions, showing excellent comprehensive performance.

[0011] 3) Reactive composite sintering aids (commercially available): Bi2O3: 0.2–0.8 wt% B2O3: 0.1~0.6 wt% (can be replaced by H3BO3 and converted to B2O3); Li2CO3: 0.2–0.6 wt% (provides Li2O equivalent); This ternary additive generates a small amount of controllable liquid phase during the heating process to promote low-temperature densification. At the same time, it undergoes a "re-curing reaction" with the main body during the heat preservation stage, avoiding the problems of high loss and low breakdown caused by the residue of traditional glass additives.

[0012] Unexpected results: Even under low-temperature sintering at 950℃, low tanδ (≤1.5%@1 kHz) and high breakdown strength (≥7 kV / mm) can still be obtained, with better batch consistency.

[0013] 4) Two-step sintering process: First, a higher temperature (T1) is used for a short time to promote the formation of the sintering neck, and then the temperature is lowered to T2 for a longer time to promote densification and inhibit abnormal grain growth. T1: 980~1040℃, hold for 5~30 min; T2: 880~950℃, maintain for 2~6 h; Heating / cooling rate: 2-5℃ / min.

[0014] This system expands the process window and improves mechanical strength and electrical stability.

[0015] The beneficial effects of this invention are: (1) Achieving higher overall electrical performance and reliability under low-temperature two-step sintering conditions: Examples 1-3 achieved bulk densities of 5.84-5.86 g / cm³ under the same two-step sintering regime (T1=1020℃15min→T2=920℃4h). 3 The tanδ was only 1.05%–1.25%, Eb reached 8.0–8.5 kV / mm, and the d33 retention rate was 91%–93%, while d33 was 176–190 pC / N and kp was 0.38–0.40. When any key measure in the comparison was removed / weakened, the above indicators showed a systematic deterioration: for example, in Comparative Example 1 (without La / Mn), tanδ increased to 2.20%, Eb decreased to 6.2 kV / mm, and the retention rate was only 78%; in Comparative Example 5 (without sintering aid), the bulk density dropped significantly to 5.62 g / cm³. 3 Meanwhile, tanδ increases to 2.80%, Eb is only 4.6 kV / mm, and d33 decreases to 140 pC / N. Therefore, this invention achieves a reliable combination of "low loss + high breakdown + low aging" without relying on higher sintering temperatures.

[0016] (2) La / Mn dual doping brings synergistic benefits of "low loss + high Eb + high retention rate": Based on Example 1 (La 0.6 mol% + Mn 0.3 mol%): Compared to Comparative Example 1 (neither of which had doping), d33 increased from 165 to 182 pC / N, tanδ decreased from 2.20% to 1.10%, Eb increased from 6.2 to 8.3 kV / mm, retention increased from 78% to 92%, and kp also increased from 0.35 to 0.39, indicating that dual doping simultaneously improves output capability and reliability. Further examining single doping: Comparative Example 2 (La only) had a d33 of 175 pC / N, which was close, but tanδ was still 1.65%, Eb was only 7.0, and retention was 84%; Comparative Example 3 (Mn only) had an even lower d33 of 158 pC / N and tanδ of 1.85%, Eb of 6.7, and retention of 82%. In Comparative Example 4, after reducing La to 0.3 mol%, tanδ=1.45%, Eb=7.4, and retention rate 86%, it was still significantly lower than that of Example 1. The above data chain shows that La and Mn in this system are not simply superimposed, but together they pull tanδ, Eb, and aging retention rate to a better range, while maintaining a high d33 / kp, thus alleviating the contradictions described in the background art.

[0017] (3) The reactive composite additive Bi2O3+B2O3+Li2CO3 takes into account both "low-temperature densification and electrical properties": Comparative Example 5 (with all additives removed) had a density of only 5.62 g / cm³ under the same sintering conditions. 3 The presence of a significant increase in tanδ (2.80%), a significant decrease in Eb (4.6 kV / mm), and a significant decrease in d33 (140 pC / N) at low temperatures indicates that the lack of additives at low temperatures leads to insufficient densification and a chain reaction that damages breakdown and polarization response. The densities of Comparative Example 6 (Bi2O3 only) and Comparative Example 7 (Bi2O3 removed, only B and Li) were 5.76 and 5.73 g / cm³, respectively. 3 The tanδ values ​​were 1.90% and 2.10%, respectively, and the Eb values ​​were 6.3 and 5.9 kV / mm, respectively, both lower than those in Example 1 (5.86, 1.10%, and 8.3). This demonstrates that the ternary composite additive exhibits "component synergy": the absence of any component simultaneously reduces density and increases loss, reduces breakdown, and consequently drags down d33 and kp.

[0018] (4) Two-step sintering can still significantly reduce losses and increase Eb and d33 under the condition of "similar density", which reflects its structural optimization value: Comparative Example 8, after being modified to a single-step process of 1020℃×4h, had a bulk density of 5.84 g / cm³. 3The density is close to 5.86 in Example 1, but tanδ deteriorates from 1.10% to 1.55%, Eb decreases from 8.3 to 7.1, d33 decreases from 182 to 170, retention decreases from 92 to 86, and kp also decreases from 0.39 to 0.36. Even with similar density, two-step sintering still results in lower loss, higher breakdown, and lower aging, indicating that its effect is not only "sintering density" but also in obtaining a structural state that is more conducive to electrical reliability.

[0019] II. Principle Analysis: From the comparative relationship, the mechanism of this invention can be summarized as follows: "densification and controlled defects / conductivity" jointly drive the improvement of overall performance. (1) The fundamental support of densification for Eb and tanδ: Comparative Example 5 has the lowest density (5.62), the lowest Eb (4.6), and the highest tanδ (2.80), indicating that porosity / underdensification will form electric field concentration and leakage conduction paths, causing premature breakdown and increasing dielectric loss, while piezoelectric output (d33=140, kp=0.31) is also hindered. After adding the ternary additive (density 5.86 in Example 1), Eb and tanδ improved significantly, indicating that the additive makes it easier to obtain high density in the material under low temperature conditions, thereby improving breakdown and reducing loss.

[0020] (2) The decisive contribution of controlled defect chemistry to “low loss-high breakdown-low aging”: Between Comparative Example 1 (5.82) and Example 1 (5.86) with similar densities, Eb increased from 6.2 to 8.3, tanδ increased from 2.20 to 1.10, and retention increased from 78 to 92. The difference is far beyond the range that can be explained by density difference, pointing to the dominant role of the doping system in conductivity / loss / polarization stability; while single-doped La or single-doped Mn cannot achieve the combination of tanδ, Eb and retention of Example 1 (see Comparative Examples 2 and 3, respectively), indicating that a better electrical stability state must be achieved through the ratio window of La / Mn dual doping.

[0021] (3) Refined control of reliability through process regime: Comparative Example 8 and Example 1 have similar densities, but Example 1 is superior in tanδ, Eb, retention rate, and d33, indicating that the two-step sintering further suppresses structural factors that lead to loss and breakdown degradation at the same level of density (as reflected in the data: loss is reduced by 0.45 percentage points, Eb is increased by 1.2 kV / mm, and retention rate is increased by 6 percentage points). Therefore, the principle of this invention can be summarized as follows: a high density base is ensured at low temperature through composite additives, and lower loss and higher breakdown / anti-aging are achieved through La / Mn double doping. Finally, electrical reliability is further optimized by two-step sintering without sacrificing density, so that Examples 1 to 3 form a performance matrix that is "comprehensively superior" to Comparative Examples 1 to 8 in Table 1.

[0022] In summary, this invention achieves higher density, lower tanδ, higher Eb and better aging retention under low-temperature sintering conditions, while maintaining high d33 and kp. It successfully alleviates the coupling contradiction between "low-temperature densification-low loss-high reliability" as described in the background technology, and exhibits significant comprehensive performance advantages and improved process usability. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Meanwhile, unless otherwise specified, the raw materials, reagents, or devices used in the following embodiments can be obtained from conventional commercial channels or by existing known methods. The following embodiments are used to explain the present invention. Unless otherwise specified, the raw materials are all commercially available analytical grade or industrial high-purity (≥99.0%), which can be purchased from conventional channels such as Sinopharm / Aladdin / Xilong. Raw materials and specifications: Bi2O3 (≥99.9%); Na2CO3 (≥99.8%, dried at 120℃ for 2 h before use); K2CO3 (≥99.5%, dried at 120℃ for 2 h before use); BaCO3 (≥99.0%); TiO2 (anatase or rutile, ≥99.0%); La2O3 (≥99.9%, pre-calcined at 900℃ for 1 h before use); MnO2 (≥99.0%); Li2CO3 (≥99.0%); H3BO3 (≥99.0%); ethanol (anhydrous); polyvinyl alcohol (PVA) (5 wt% aqueous solution as binder).

[0024] Example 1

[0025] A sodium bismuth titanate-based piezoelectric ceramic material and its preparation method: (1) Target formulation: Main component: 0.78 BNT - 0.16 BKT - 0.06 BT (mole fraction); Doping: La2O3 0.6 mol%, MnO2 0.3 mol% (both based on ABO3); Sintering aids (relative to the mass of main powder): Bi2O3 0.5wt% + B2O3 0.3wt% (converted to H3BO3) + Li2CO3 0.4wt%; (2) Weighing and mixing (taking the preparation of approximately 100g of pre-calcined main powder as an example): Weigh Bi₂O₃ (50.98g), Na₂CO₃ (9.65g), K₂CO₃ (2.58g), BaCO₃ (5.53g), and TiO₂ (37.33g) according to stoichiometry to form a bulk of 0.78BNT-0.16BKT-0.06BT; Then add La2O3 (0.6 mol%, 0.914 g) and MnO2 (0.3 mol%, 0.122 g) according to ABO3.

[0026] The above powder was added to anhydrous ethanol, and the ball milling media was zirconia balls (φ5mm) at a ball-to-powder ratio of 2:1. The mixture was ball-milled for 12 hours. After ball milling, the powder was dried (at 80℃) and passed through an 80-mesh sieve.

[0027] (3) Pre-calcination (solid-phase reaction): The sieved powder was placed in a covered alumina crucible and heated to 850℃ at a rate of 3℃ / min, held for 2 h, and then allowed to cool naturally. After pre-calcination, it was slightly crushed, then wet-milled with ethanol for 6 h, dried, and sieved.

[0028] (4) Adding reactive composite additives and granulation: Bi₂O₃ (0.50 g), H₃BO₃ (0.533 g, equivalent to 0.3 wt% B₂O₃), and Li₂CO₃ (0.40 g) were added to the main powder after secondary ball milling, and the powder was wet-milled for 2 h to ensure uniformity. After drying, PVA solution was added to make the PVA mass fraction 1.5 wt% (relative to the powder), and the powder was granulated by passing it through a 40-mesh sieve.

[0029] (5) Molding and glue removal: Pressed disc: 12 mm in diameter, approximately 1.2 mm thick; unidirectional pressing 150 MPa.

[0030] Glue removal: Heat up to 550℃ at a rate of 1℃ / min and hold for 2 hours.

[0031] (6) Two-step sintering: Placed in a covered crucible, sintered in air atmosphere: T1=1020℃ for 15 min; then cooled to T2=920℃ for 4 h; the heating / cooling rate was 3℃ / min. After sintering, both sides were ground smooth to a thickness of 1.0 mm.

[0032] (7) Electrodes and Polarization: The electrodes were sintered by brushing silver paste onto both sides and holding at 600℃ for 10 min.

[0033] Polarization: The sample was immersed in silicone oil, a DC electric field of 4.0 kV / mm was applied, the temperature was 80℃, and the temperature was held for 20 min. Then, it was cooled to room temperature while maintaining the electric field to obtain sodium bismuth titanate-based piezoelectric ceramic material.

[0034] Example 2

[0035] A sodium bismuth titanate-based piezoelectric ceramic material and its preparation method: (1) Target formulation: Main component: 0.74 BNT - 0.18 BKT - 0.08 BT (mole fraction); Doping: La2O3 0.8 mol%, MnO2 0.4 mol% (both based on ABO3); Sintering aids (relative to the mass of main powder): Bi2O3 0.6wt% + B2O3 0.5wt% (converted to H3BO3) + Li2CO3 0.3wt%; (2) Weighing and mixing (taking the preparation of approximately 100g of pre-calcined main powder as an example): Weigh Bi₂O₃ (49.50g), Na₂CO₃ (9.08g), K₂CO₃ (3.19g), BaCO₃ (7.29g), and TiO₂ (36.85g) according to stoichiometry to form a bulk of 0.74BNT-0.18BKT-0.08BT; Then add La2O3 (0.8 mol%, 1.203 g) and MnO2 (0.4 mol%, 0.161 g) according to ABO3.

[0036] The above powder was added to anhydrous ethanol, and the ball milling media was zirconia balls (φ5mm) at a ball-to-powder ratio of 2:1. The mixture was ball-milled for 12 hours. After ball milling, the powder was dried (at 80℃) and passed through an 80-mesh sieve.

[0037] (3) Pre-calcination (solid-phase reaction): The sieved powder was placed in a covered alumina crucible and heated to 850℃ at a rate of 3℃ / min, held for 2 h, and then allowed to cool naturally. After pre-calcination, it was slightly crushed, then wet-milled with ethanol for 6 h, dried, and sieved.

[0038] (4) Adding reactive composite additives and granulation: Bi₂O₃ (0.60 g), H₃BO₃ (0.888 g, equivalent to 0.5 wt% B₂O₃), and Li₂CO₃ (0.30 g) were added to the main powder after secondary ball milling, and wet ball milling was performed for 2 h to ensure homogeneity. After drying, PVA solution was added to make the PVA mass fraction 1.5 wt% (relative to the powder), and the powder was granulated by passing it through a 40-mesh sieve.

[0039] (5) Molding and glue removal: Pressed disc: 12 mm in diameter, approximately 1.2 mm thick; unidirectional pressing 150 MPa.

[0040] Glue removal: Heat up to 550℃ at a rate of 1℃ / min and hold for 2 hours.

[0041] (6) Two-step sintering: Placed in a covered crucible, sintered in air atmosphere: T1=1020℃ for 15 min; then cooled to T2=920℃ for 4 h; the heating / cooling rate was 3℃ / min. After sintering, both sides were ground smooth to a thickness of 1.0 mm.

[0042] (7) Electrodes and Polarization: The electrodes were sintered by brushing silver paste onto both sides and holding at 600℃ for 10 min.

[0043] Polarization: The sample was immersed in silicone oil, a DC electric field of 4.0 kV / mm was applied, the temperature was 80℃, and the temperature was held for 20 min. Then, it was cooled to room temperature while maintaining the electric field to obtain sodium bismuth titanate-based piezoelectric ceramic material.

[0044] Example 3

[0045] A sodium bismuth titanate-based piezoelectric ceramic material and its preparation method: (1) Target formulation: Main component: 0.78 BNT - 0.10 BKT - 0.12 BT (mole fraction); Doping: La2O3 0.5 mol%, MnO2 0.25 mol% (both based on ABO3); Sintering aids (relative to the mass of main powder): Bi2O3 0.4wt% + B2O3 0.2wt% (converted to H3BO3) + Li2CO3 0.5wt%; (2) Weighing and mixing (taking the preparation of approximately 100g of pre-calcined main powder as an example): Weigh Bi₂O₃ (47.30g), Na₂CO₃ (9.55g), K₂CO₃ (1.60g), BaCO₃ (10.93g), and TiO₂ (36.85g) according to stoichiometry to form a bulk of 0.78BNT-0.10BKT-0.12BT; Then add La2O3 (0.5 mol%, 0.752 g) and MnO2 (0.25 mol%, 0.100 g) according to ABO3.

[0046] The above powder was added to anhydrous ethanol, and the ball milling media was zirconia balls (φ5mm) at a ball-to-powder ratio of 2:1. The mixture was ball-milled for 12 hours. After ball milling, the powder was dried (at 80℃) and passed through an 80-mesh sieve.

[0047] (3) Pre-calcination (solid-phase reaction): The sieved powder was placed in a covered alumina crucible and heated to 850℃ at a rate of 3℃ / min, held for 2 h, and then allowed to cool naturally. After pre-calcination, it was slightly crushed, then wet-milled with ethanol for 6 h, dried, and sieved.

[0048] (4) Adding reactive composite additives and granulation: Bi₂O₃ (0.50 g), H₃BO₃ (0.533 g, equivalent to 0.3 wt% B₂O₃), and Li₂CO₃ (0.40 g) were added to the main powder after secondary ball milling, and the powder was wet-milled for 2 h to ensure uniformity. After drying, PVA solution was added to make the PVA mass fraction 1.5 wt% (relative to the powder), and the powder was granulated by passing it through a 40-mesh sieve.

[0049] (5) Molding and glue removal: Pressed disc: 12 mm in diameter, approximately 1.2 mm thick; unidirectional pressing 150 MPa.

[0050] Glue removal: Heat up to 550℃ at a rate of 1℃ / min and hold for 2 hours.

[0051] (6) Two-step sintering: Placed in a covered crucible, sintered in air atmosphere: T1=1020℃ for 15 min; then cooled to T2=920℃ for 4 h; the heating / cooling rate was 3℃ / min. After sintering, both sides were ground smooth to a thickness of 1.0 mm.

[0052] (7) Electrodes and Polarization: The electrodes were sintered by brushing silver paste onto both sides and holding at 600℃ for 10 min.

[0053] Polarization: The sample was immersed in silicone oil, a DC electric field of 4.0 kV / mm was applied, the temperature was 80℃, and the temperature was held for 20 min. Then, it was cooled to room temperature while maintaining the electric field to obtain sodium bismuth titanate-based piezoelectric ceramic material.

[0054] Comparative Example 1 Comparative Example 1 served as the control group for Example 1. La2O3 and MnO2 were removed from Example 1, while the remaining raw materials, raw material amounts, and preparation steps remained consistent with those in Example 1, ultimately yielding a piezoelectric ceramic material.

[0055] Comparative Example 2 Comparative Example 2 served as the control group for Example 1. MnO2 was removed from Example 1, while the remaining raw materials, raw material amounts, and preparation steps remained consistent with those in Example 1, ultimately yielding a piezoelectric ceramic material.

[0056] Comparative Example 3 Comparative Example 3 served as the control group for Example 1. La2O3 was removed from Example 1, while the remaining raw materials, raw material amounts, and preparation steps remained consistent with those in Example 1, ultimately yielding a piezoelectric ceramic material.

[0057] Comparative Example 4 Comparative Example 4 served as the control group for Example 1. The amount of La2O3 in Example 1 was adjusted to 0.3 mol% (0.457 g), while the remaining raw materials, raw material amounts, and preparation steps remained consistent with those in Example 1, ultimately yielding piezoelectric ceramic materials.

[0058] Comparative Example 5 Comparative Example 5 served as the control group for Example 1. Bi2O3, B2O3, and Li2CO3 were removed from Example 1, while the remaining raw materials, raw material amounts, and preparation steps remained consistent with those in Example 1, ultimately yielding a piezoelectric ceramic material.

[0059] Comparative Example 6 Comparative Example 6 served as the control group for Example 1. B2O3 and Li2CO3 were removed from Example 1, while the remaining raw materials, raw material amounts, and preparation steps remained consistent with those in Example 1, ultimately yielding a piezoelectric ceramic material.

[0060] Comparative Example 7 Comparative Example 7 served as the control group for Example 1. Bi2O3 was removed from Example 1, while the remaining raw materials, raw material amounts, and preparation steps remained consistent with those in Example 1, ultimately yielding a piezoelectric ceramic material.

[0061] Comparative Example 8 Comparative Example 8 served as the control group for Example 1. The two-step sintering was eliminated and replaced with a single-step sintering: holding at 1020℃ for 4 hours. The remaining raw materials, raw material amounts, and preparation steps remained consistent with those in Example 1, and the piezoelectric ceramic material was finally obtained.

[0062] Test Example 1 The piezoelectric ceramic materials prepared in Examples 1 to 3 and Comparative Examples 1 to 8 were subjected to performance tests. The performance test process is as follows, and the test results are shown in Table 1: (1) Volume density: Method: Archimedes method (GB / T 9966); Procedure: Dry the sample at 120℃ for 1 hour, cool to room temperature and weigh the dry mass m1; Vacuum immersion in water: immerse at -0.08 MPa for 30 minutes, then return to normal pressure and immerse for 2 hours; weigh in water m2 (suspended scale); weigh the saturated mass m3 after wiping the surface; bulk density ρ = m1 / (m3-m2) × ρ 水 .

[0063] (2) Dielectric constant εr and dielectric loss tanδ: Instruments: LCR meter (1 kHz / 10 kHz), test voltage 1 Vrms; Conditions: 25℃; additional temperature scan (25~120℃, equilibrate for 10 min every 10℃); Outputs: εr (1kHz), tanδ (1kHz); and the maximum value and volatility of tanδ at 25–120℃.

[0064] (3) Piezoelectric constant d33: Instrument: d33 instrument (quasi-static method); Conditions: Initial d33 was measured 24 h after polarization; and aging was performed: the product was placed at 85℃ for 168 h (without electric field), cooled for 2 h, and then d33 was measured. The d33 retention rate (%) after aging at 85℃ for 168 h was calculated.

[0065] (4) Electromechanical coupling coefficient kp: Method: Resonance-anti-resonance method (impedance analyzer), calculated according to IEC 60483 / IEEE standard (radial mode of disc); Output: kp.

[0066] (5) Breakdown strength Eb: Medium: Test in silicone oil to avoid surface flashover; Voltage loading: DC boost rate 0.5 kV / s or 1 kV / s, record breakdown voltage Vb; Calculation: Eb = Vb / thickness (mm), unit kV / mm.

[0067] Table 1 Test Results

[0068] Analysis of the data in Table 1: (1) Overall evaluation: As shown in Table 1, Examples 1 to 3 prepared by the present invention using the synergistic scheme of "main body solid solution phase boundary regulation + controlled defect chemistry (La / Mn dual doping) + reactive composite sintering aid + two-step sintering" are superior to Comparative Examples 1 to 8 in all performance indicators.

[0069] Examples 1-3 all achieved high density (bulk density 5.84-5.86 g / cm³). 3 It exhibits excellent piezoelectric properties (d33 is 176–190 pC / N, kp is 0.38–0.40), extremely low dielectric loss (tanδ is 1.05%–1.25%), high breakdown strength (Eb is 8.0–8.5 kV / mm), and excellent aging stability (d33 retention rate is 91%–93%).

[0070] Overall, the technical solution of this invention successfully resolves the contradictions of existing BNT-based ceramics, such as difficulty in achieving low-temperature densification, high loss, and poor stability.

[0071] (2) Analysis of the effect of doping modification on performance (Example 1 vs. Comparative Examples 1-4): Comparative Examples 1-4 are control experiments on the La2O3 and MnO2 doped systems in Example 1. The specific analysis is as follows: Synergistic Effect of Dual Doping (Example 1 vs. Comparative Example 1): Data Comparison: Compared with Comparative Example 1 without any dopant, Example 1 (with 0.6 mol% La + 0.3 mol% Mn) showed an increase in d33 from 165 to 182 pC / N, a significant decrease in tanδ from 2.20% to 1.10%, an increase in Eb from 6.2 to 8.3 kV / mm, and a substantial increase in d33 retention from 78% to 92%. Analysis: This confirms the significant synergistic effect of dual doping with La and Mn. La, as a donor dopant, improves piezoelectric activity (d33), while Mn, as an acceptor dopant, forms a defect dipole, effectively reducing losses (tanδ), improving breakdown strength (Eb), and enhancing anti-aging ability (retention rate).

[0072] The effect of Mn (acceptor doping) (Example 1 vs. Comparative Example 2): Data comparison: Comparative Example 2 only added La and no Mn. Compared with Example 1, Comparative Example 2 has a higher tanδ (1.65% vs. 1.10%), lower Eb (7.0 vs. 8.3 kV / mm), and lower d33 retention (84% vs. 92%). Analysis: This shows that the introduction of MnO2 is crucial for reducing dielectric loss, improving breakdown strength, and enhancing aging stability. The absence of Mn prevents the material from forming sufficient defect dipoles to pin domain walls or suppress leakage conduction, resulting in increased loss and decreased stability.

[0073] The role of La (donor dopant) (Example 1 vs. Comparative Examples 3 and 4): Data comparison: Comparative Example 3, with only Mn added and no La added, had a d33 of only 158 pC / N, significantly lower than the 182 pC / N of Example 1. Comparative Example 4, although adding La, did so in a small amount (0.3 mol%), and while its d33 (178 pC / N) and tanδ (1.45%) were better than Comparative Example 3, they were still inferior to Example 1. Analysis: This indicates that La2O3, as a donor dopant, primarily promotes domain wall movement and improves the piezoelectric response (d33). La deficiency or insufficiency leads to a decrease in piezoelectric performance. Simultaneously, an appropriate amount of La also helps suppress oxygen vacancy-related conductivity, further optimizing performance in conjunction with Mn.

[0074] (3) Analysis of the influence of sintering aids on low-temperature densification and performance (Example 1 vs. Comparative Example 5 vs. 7): Comparative Example 5 vs. 7 is a control experiment for the "Bi2O3+B2O3+Li2CO3" composite sintering aid in Example 1. The specific analysis is as follows: Necessity of Composite Additives (Example 1 vs. Comparative Example 5): Data Comparison: Comparative Example 5, without any sintering additives, has a bulk density of only 5.62 g / cm³. 3 It is much lower than the 5.86 g / cm³ in Example 1. 3 Meanwhile, it exhibits extremely low Eb (4.6 kV / mm), extremely high tanδ (2.80%), and a d33 of only 140 pC / N. Analysis: This indicates that densification of BNT-based ceramics cannot be achieved without additives under low-temperature conditions (two-step sintering T2 = 920℃). The presence of porosity severely degrades breakdown strength and dielectric loss, hinders polarization, and results in extremely poor piezoelectric properties. The composite additives of this invention are key to achieving low-temperature sintering.

[0075] Synergistic effect of adjuvant components (Example 1 vs. Comparative Examples 6 and 7): Data comparison: The bulk densities of Comparative Example 6 (without B and Li, only Bi) and Comparative Example 7 (without Bi, only B and Li) were 5.76 g / cm³. 3 and 5.73 g / cm 3 The results were all lower than in Example 1. The corresponding electrical properties (d33, tanδ, Eb) were also inferior to those of Example 1. Analysis: This indicates that a single or partial additive cannot achieve the effect of the ternary composite additive (Bi-B-Li). This ternary additive may form a low-melting-point liquid phase during sintering to promote densification, and undergo a "re-curing reaction" during the holding stage, thus ensuring high density while avoiding performance degradation caused by glass phase residue. The absence of any component will affect the formation or wettability of the liquid phase, leading to a decrease in density and electrical properties.

[0076] (4) Analysis of the impact of sintering regime (Example 1 vs Comparative Example 8): Comparative Example 8 adjusted the "two-step sintering" process of Example 1 to the traditional single-step sintering.

[0077] Advantages of two-step sintering (Example 1 vs. Comparative Example 8): Data comparison: Although the bulk density of Comparative Example 8 (single-step sintering at 1020℃ for 4 hours) was 5.84 g / cm³ 3 ) and Example 1 (5.86 g / cm 3The dielectric constant (Tb) was comparable to that of Example 8, but its electrical properties were significantly inferior: tanδ was 1.55% (1.10% in Example 1), Eb was 7.1 kV / mm (8.3 kV / mm in Example 1), and d33 was 170 pC / N (182 pC / N in Example 1). Analysis: This indicates that the two-step sintering process (T1 high temperature, short-time necking; T2 low temperature, long-time densification) not only contributes to densification but, more importantly, suppresses abnormal grain growth and optimizes the microstructure. The single-step high-temperature sintering of Comparative Example 8 may have resulted in coarse or inhomogeneous grains, thereby increasing dielectric loss and reducing breakdown strength and piezoelectric properties. Two-step sintering is crucial for obtaining high-quality ceramics with "high Eb + low tanδ".

[0078] In summary, the test results in Table 1 fully demonstrate the advanced nature of the technical solution of this invention: (1) La / Mn dual doping achieves a balance between high voltage electroactivity and low loss and high stability; (2) Bi-B-Li composite additive ensures high densification at low temperature without compromising electrical performance; (3) the two-step sintering process further optimizes the microstructure and improves the breakdown strength and overall electrical performance. The synergistic effect of these three factors enables Examples 1-3 to achieve excellent comprehensive performance under low-temperature sintering conditions.

[0079] It should be noted that, in this document, terms such as “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0080] 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 sodium bismuth titanate-based piezoelectric ceramic material, characterized in that, Based on ABO3, the bulk composition of the piezoelectric ceramic material, expressed as a mole fraction, is as follows: (1-xy)BNT+xBKT+yBT; in: BNT=(Bi 0.5 And 0.5 )TiO3 BKT=(Bi 0.5 K 0.5 )TiO3; BT = BaTiO3; And it satisfies: 0.10≤x≤0.18, 0.06≤y≤0.12; Furthermore, the piezoelectric ceramic material also includes doping components La2O3 and MnO2, calculated as ABO3; in: The doping concentration of La2O3 is 0.4–0.9 mol%; The doping amount of MnO2 is 0.2–0.5 mol.

2. The bismuth titanate-based piezoelectric ceramic material according to claim 1, characterized in that, The molar ratio of La2O3 to MnO2 is (1.2~2.5):

1.

3. The bismuth titanate-based piezoelectric ceramic material according to claim 1, characterized in that, The piezoelectric ceramic material also includes a reactive composite sintering aid relative to the bulk mass; The reactive composite sintering aids include Bi2O3, B2O3 and Li2CO3; in: Bi2O3 content was 0.2–0.8 wt%; B2O3 content is 0.1–0.6 wt%; The Li2CO3 content is 0.2–0.6 wt%.

4. The sodium bismuth titanate-based piezoelectric ceramic material according to claim 1, characterized in that, The piezoelectric ceramic material is obtained by two-step sintering, which includes: first holding at a temperature of T1 for t1, and then lowering to a temperature of T2 and holding for t2; wherein T1 is 980~1040℃ and t1 is 5~30min, and T2 is 880~950℃ and t2 is 2~6h.

5. The sodium bismuth titanate-based piezoelectric ceramic material according to claim 4, characterized in that, The heating and / or cooling rates for the two-step sintering are 2–5 °C / min.

6. The bismuth titanate-based piezoelectric ceramic material according to claim 1, characterized in that, The dielectric loss tanδ of the material is ≤1.5% at 1 kHz and 25 °C.

7. The sodium bismuth titanate-based piezoelectric ceramic material according to claim 1, characterized in that, The breakdown strength of the material is Eb≥7kV / mm.

8. A method for preparing a sodium bismuth titanate-based piezoelectric ceramic material according to any one of claims 1 to 7, characterized in that, Includes the following steps: (1) Prepare and mix the main components (1-xy)BNT+xBKT+yBT, and add La2O3 and MnO2 at the same time to obtain mixed powder; (2) The mixed powder is pre-calcined to form a main phase powder; (3) Add reactive composite sintering aids Bi2O3, B2O3 and Li2CO3 to the pre-fired main phase powder, mix evenly and then form a green body; (4) After removing the binder from the green body, two-step sintering is carried out to obtain sintered ceramics; (5) Apply electrodes to the sintered ceramic and polarize it to obtain sodium bismuth titanate-based piezoelectric ceramic material.

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