High-stability lead-free BNT-BT-BF piezoelectric ceramic as well as preparation method and high-temperature application thereof

Abstract

According to the BiFeO3-doped lead-free BNT-BT-based piezoelectric ceramic provided by the invention, collaborative optimization of d33 = 132pC / N and Td = 105 DEG C is realized by regulating and controlling the phase boundary ratio (R3c: P4mm = 4: 6) and the grain size (1.2-1.5 microns). The ceramic is prepared by adopting a solid phase method, is simple in process and low in cost, is suitable for electronic devices in a high-temperature severe environment, and has the advantages of environmental protection and high performance.

Description

Technical Field:

[0001] The present invention belongs to the technical field of functional ceramic materials, and particularly relates to a lead-free BNT-BT-based piezoelectric ceramic optimized by BiFeO3 doping. Through the synergistic regulation of the morphotropic phase boundary (MPB) and grain size, high piezoelectric performance (d 33 ≥130 pC / N) and wide-temperature thermal stability (Td≥100 °C) are achieved, which is applicable to electronic devices such as high-temperature sensors and transducers. Background Art:

[0002] The use of lead-based piezoelectric ceramics (such as PZT) is restricted by international environmental protection regulations due to lead toxicity, and lead-free piezoelectric ceramics have become a research hotspot. BNT-BT (0.94Bi 0.5 Na 0.5 TiO3 - 0.06BaTiO3) system has a high piezoelectric response (d 33 ≈150 pC / N) near the morphotropic phase boundary (MPB), but its depolarization temperature (Td) is usually lower than 80 °C, and the performance decays due to the migration of oxygen vacancies at high temperatures. Existing improvement methods include: 1. Doping modification: For example, although KNN doping improves the energy storage density, the piezoelectric constant decreases (d 33 <100 pC / N); 2. Composite phase design: For example, the BNT-BT-BiT system broadens the temperature range (Td≈120 °C), but the process is complex and the cost is high.

[0003] In view of this, it is urgent to develop a lead-free piezoelectric ceramic with a simple process that takes into account both high piezoelectric performance and wide-temperature stability. Summary of the Invention:

[0004] To solve the above problems, the present invention proposes a BiFeO3 (BF)-doped BNT-BT-based piezoelectric ceramic, whose chemical general formula is: (1 - x)(0.94Bi 0.5 Na 0.5 TiO3 - 0.06BaTiO3) - xBiFeO3, where x = 0.08 - 0.12. Performance breakthroughs are achieved through the following technical means:

[0005] Preferably, phase structure regulation: When x = 0.10, the volume ratio of the rhombohedral phase (R3c) to the tetragonal phase (P4mm) is optimized to 4:6, forming a morphotropic phase boundary (MPB) with strong piezoelectric response. In the XRD pattern, the (111) peak splits into (003) and (021), and the (200) peak splits into (002) and (200);

[0006] Preferably, grain size optimization: BF doping inhibits grain boundary migration, and the grain size reaches 1.2 - 1.5 μm, reducing the activation energy of domain wall motion and improving the polarization efficiency;

[0007] Preferably, oxygen vacancy suppression: Fe 3+ Partially replace Ti 4+ Reduce the oxygen vacancy concentration and lower the leakage current.

[0008] Preferably, raw material mixing: Weigh Bi2O3 (purity ≥ 99.9%), BaCO3 (≥ 99%), TiO2 (≥ 99%), Na2CO3 (≥ 99.99%), Fe2O3 (≥ 99%) according to stoichiometry, and ball mill in ethanol medium for 12 hours (ball-to-material ratio 5:1, rotation speed 300 rpm);

[0009] Preferably, pre-sintering treatment: After drying, calcine at 680 °C for 1 hour, and ball mill for 24 hours until the particle size D50 ≤ 1 μm;

[0010] Preferably, forming and sintering: Add 5 wt% PVA binder for granulation, press into a Φ13 mm × 1 mm disc (pressure 9 MPa), and sinter at 1050 °C for 2 hours (heating rate 5 °C / min) to obtain a ceramic body with a relative density ≥ 98%;

[0011] Preferably, electrode and poling: After surface polishing, apply silver paste electrodes, and apply an electric field of 3 kV / mm in a silicone oil bath for poling for 15 minutes (temperature 120 °C).

[0013] Compared with the prior art, the present invention has the following beneficial effects: Strong piezoelectric performance: When x = 0.10, d 33 = 132 pC / N, g 33 = 26.11×10- 3 Vm / N; Good thermal stability: Depolarization temperature Td = 105 °C (tested at 1 kHz), and the fluctuation rate of d 33 is < 10% in the range of 25 - 150 °C; Great application potential: It has both high voltage output (g 33 ) and low dielectric loss (tanδ < 0.05), and is suitable for high-temperature vibration sensors, ultrasonic transducers, etc. Description of the drawings:

[0013] Figure 1 It is the temperature dependence characteristic diagram of d 33 for BNT-BT-0.10BF ceramics;

[0014] Figure 2 It is the impedance and phase angle spectrum showing the resonance and anti-resonance frequency diagrams of (a) BNT-BT-0.08BF ceramics, (b) BNT-BT-0.10BF ceramics, and (c) BNT-BT-0.12BF ceramics;

[0015] Figure 3 Surface microstructure of (a) BNT-BT-0.08BF, (b) BNT-BT-0.10BF, (c) BNTBT-0.12BF ceramics. (d) Variation of average grain size with x value. Specific implementation method:

[0016] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present invention. The present invention is further described in detail below in conjunction with the accompanying drawings and examples, but the protection scope of the present invention is not limited to the following examples.

[0017] Example 1 Composition: x = 0.10, i.e. BNT-BT-0.10BF; Process: Prepared according to the above method, the density of the ceramic after sintering is 5.82g / cm 3 ; Performance: D 33 =132pC / N,g 33 =26.11×10 -3 Vm / N, Td = 105°C, Q m =124(1kHz).

[0017] Preparation method of high stability lead-free BNT-BT-BF piezoelectric ceramics:

[0019] (1) Ingredients and ball milling Bi2O3 (purity ≥99.9%), BaCO3 (≥99%), TiO2 (≥99%), Na2CO3 (≥99.99%), and Fe2O3 (≥99%) were weighed according to chemical quantification and ball-milled in ethanol medium for 12 hours (ball-to-material ratio 5:1, rotation speed 300 rpm).

[0020] (2) Pre-sintering and secondary ball milling The fully mixed slurry was dried and transferred to a crucible. The temperature was raised from room temperature to 850°C at a rate of 5°C / min, then kept at the highest temperature for 2 hours and cooled naturally. After drying, it was calcined at 680°C for 1 hour and ball-milled for 24 hours until the particle size D50 ≤ 1 μm.

[0021] (3) Molding and sintering 5 wt% PVA binder was added to granulate, pressed into Φ13 mm×1 mm discs (pressure 9 MPa), and sintered at 1050°C for 2 hours (heating rate 5°C / min) to obtain a ceramic body with a density ≥98%.

[0022] (4) Debonding The debinded wafers are sintered in an air-free environment. The sintering process is as follows: starting from 20 °C, first heating at a heating rate of 5 °C / min to 110 °C, holding for 30 min, heating to 360 °C within 84 min and holding for 30 min, then heating to 520 °C within 54 min, holding for 30 min, and then naturally cooling.

[0023] (5) Silver plating and polarization The surface of the sintered ceramic wafers is polished flat with a sanding disc, then silver paste is coated on both sides, placed in a muffle furnace, heated to 550 °C at 5 °C / min and held for 40 min, and then naturally cooled. The ceramic wafers covered with silver electrodes are placed on a baking plate and heated for 10 - 20 min, polished on the surface, coated with silver paste electrodes, and polarized in a silicone oil bath with an electric field of 3 kV / mm for 15 minutes (temperature 120 °C).

[0024] The properties of the lead-free piezoelectric ceramics prepared in the above experimental groups and the control group were tested, and the results are shown in Table 1.

[0025] Table 1 Properties of lead-free piezoelectric ceramics in each experimental group and the control group

[0026] As can be seen from Chart 1, the piezoelectric constant of BNT-BT-0.10BF ceramics has increased significantly. To test its thermal stability, the ceramic samples were tested at varying temperatures of d 33 below. Figure 1 The results shown demonstrate the non-linear relationship between the piezoelectric constant and temperature, which is characterized by an initial increase followed by a decrease. The variation pattern of d 33 is the same as that of d 33 The introduction of BiFeO3 leads to a higher Td, thereby enhancing the piezoelectricity and thermal stability of the BNT-BT solid solution.

[0027] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A lead-free piezoelectric ceramic, characterized in that, Its chemical general formula is: (1 - x)(0.94Bi 0.5 Na 0.5 TiO3 - 0.06BaTiO3)-xBiFeO3, where x = 0.08 to 0.12, and when x = 0.10, the volume ratio of the rhombohedral phase (R3c) to the tetragonal phase (P4mm) is (40 ± 5%):(60 ± 5%).

2. The ceramic according to claim 1, having a grain size of 1.2 to 1.5 μm and an oxygen vacancy concentration ≤ 1×10 17 cm -3 .

3. The preparation method according to claim 1, characterized in that, The sintering temperature is 1050 ± 10 °C, the heat preservation time is 2 ± 0.5 hours, and the polarization electric field strength is 3 ± 0.5 kV / mm.

4. The application of the ceramic according to claim 1 in high-temperature (≥ 100 °C) piezoelectric devices, including but not limited to sensors, ultrasonic transducers or energy harvesting devices.

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