Preparation method capable of remarkably improving piezoelectric property of bismuth layered piezoelectric ceramic

Abstract

The invention provides a preparation method capable of remarkably improving the piezoelectric property of bismuth layered piezoelectric ceramic so as to solve the problem of low piezoelectric activity of the bismuth layered piezoelectric ceramic. According to the method, one step is added after a bismuth layered piezoelectric ceramic block is sintered by a conventional solid-phase method, that is, a certain pressure is applied for a period of time at the temperature lower than the sintering temperature by 200 DEG C or below, so that the bismuth layered piezoelectric ceramic block is subjected to compression deformation, crystal grains are rearranged, and part of the bismuth layered piezoelectric ceramic block is subjected to preferred orientation growth; the density rho of the compact ceramic bismuth layered piezoelectric ceramic block is increased by 1.65%-3.43%, the d33 of the compact ceramic bismuth layered piezoelectric ceramic block is increased by 52.57%-155.74%, the dielectric constant epsilon r of the compact ceramic bismuth layered piezoelectric ceramic block is increased by 14.52%-195.35%, and the dielectric constant epsilon r of the compact ceramic bismuth layered piezoelectric ceramic block is increased by 52.57%-155.74%. Therefore, the bismuth layered piezoelectric ceramic prepared by the method is more suitable for preparing sensitive piezoelectric elements of high-temperature piezoelectric sensors for monitoring vibration states of aero-engines, gas turbines and reactors.

Description

Technical Field

[0001] The present invention relates to the technical field of piezoelectric materials, and in particular to a preparation method capable of significantly improving the piezoelectric properties of bismuth layered piezoelectric ceramics. Background Art

[0002] Various devices such as transducers, drivers, sensors, etc. made of piezoelectric ceramics have important applications in various fields of modern industry such as information technology, optoelectronics technology, precision control technology and non-destructive testing. Traditional piezoelectric ceramics represented by lead zirconate titanate (PZT) have become the most widely used piezoelectric ceramic materials due to their excellent piezoelectric and dielectric properties. At present, most commercial PZT-based piezoelectric ceramic materials are modified around PZT with a quasi-isotropic phase boundary composition, and their Curie temperature T C The temperature is usually below 380°C, which makes it difficult to meet the application requirements of piezoelectric sensors in high-temperature working environments (T>300°C) such as aerospace, nuclear energy development, geological exploration, and petrochemical industry.

[0003] The general chemical formula is (Bi2O2) 2+ (A m-1 B m O 3m+1 ) 2- The bismuth layered structure ferroelectric (BLSF) is (Bi2O2) 2+ The layers are sandwiched between perovskite-like layers (A m-1 B m O 3m+1 ) 2- And they are arranged alternately along the c-axis of the unit cell. A is a +1, +2, +3 cation or its composite ion group suitable for 12 coordination, B is a +3, +4, +5, +6 metal ion or its composite ion group suitable for 6 coordination, and m is the number of BO6 octahedrons in the perovskite layer. Bismuth layered piezoelectric ceramics have a high Curie temperature (T C Usually above 600℃), good fatigue resistance, small dielectric loss and other advantages, it has important application prospects in high temperature environment.

[0004] Due to the special crystal structure of bismuth layered piezoelectric ceramics, its spontaneous polarization is limited to the ab plane, its piezoelectric activity is low, and the piezoelectric constant d 33 Usually less than 10pC / N. For example, pure CaBi2Nb2O9 (CBN), Bi4Ti3O 12 (BIT) and CaBi2Ta2O9(CBTa) ceramics 33 The values are all around 5pC / N~6pC / N.

[0005] In order to enhance the piezoelectric activity of bismuth layered piezoelectric ceramics, ion doping is usually used to regulate its components and thus improve its piezoelectric properties. For example, the piezoelectric constant d of (Li, Bi, Ce) co-doped CBN ceramics is 33 It can be increased from 6pC / N to 20.3pC / N; the piezoelectric constant of (Ce, W, Nb) co-doped BIT ceramics can increase from 5pC / N to 38pC / N. Although ion doping can effectively enhance its piezoelectric activity, doping usually leads to a significant decrease in its Curie temperature. For example, the Curie temperature of (Li, Bi, Ce) modified CBN is about 906℃, which is nearly 40℃ lower than that of pure CBN; and the Curie temperature of (Ce, W, Nb) doped modified BIT is 640℃, which is 35℃ lower than that of pure BIT. The decrease in Curie temperature is not conducive to expanding the service temperature range of high-temperature piezoelectric sensors, and it is difficult to make any major breakthroughs in the piezoelectric performance of bismuth layered piezoelectric ceramics using ion doping.

[0006] Improvement of the preparation process is also an effective way to improve the performance of piezoelectric ceramics. For example, the CaBi2Nb2O9 produced by spark plasma sintering (SPS) has a 33 The piezoelectric constant of CaBi2Nb2O9 prepared by template grain growth method (TGG) is 19.5pC / N. 33 It can be about 17.8pC / N. Compared with CaBi2Nb2O9 ceramics prepared by traditional electronic ceramic preparation process, the piezoelectric constant d 33 Although SPS and TGG can effectively enhance piezoelectricity, SPS equipment is expensive, which is not conducive to cost control; while the TGG method is complex and the density of the prepared ceramic body is low, which is not conducive to improving the high-temperature insulation of the material. Summary of the Invention

[0007] The present invention aims to provide a preparation method that can significantly improve the piezoelectric properties of bismuth layered piezoelectric ceramics, in particular to a method that can significantly improve the piezoelectric properties of (Bi2O2)(A m-1 B m O 3m+1 ) chemical formula to prepare a piezoelectrically active bismuth layered piezoelectric ceramic, to address the problem of low piezoelectric activity of bismuth layered piezoelectric ceramics. This preparation method involves adding a step after sintering the bismuth layered piezoelectric ceramic block by the conventional solid-phase method, namely, applying a certain pressure for a period of time at a temperature within 200°C below the sintering temperature to cause the bismuth layered piezoelectric ceramic block to undergo compression deformation, rearrange the grains, and partially grow in a preferred orientation, thereby obtaining a dense bismuth layered piezoelectric ceramic block with a textured microstructure, with a density ρ increased by between 1.65% and 3.43%, d 33 The improvement range is between 52.57% and 155.74%, and the dielectric constant εr The improvement range is between 14.52% and 195.35%, which makes the bismuth layered piezoelectric ceramics prepared by the present invention more suitable for preparing sensitive piezoelectric elements of high-temperature piezoelectric sensors for vibration status monitoring of aircraft engines, gas turbines, and reactors.

[0008] To achieve the above-mentioned purpose of the present invention, the present invention is implemented by adopting the following technical solutions:

[0009] The present invention provides a preparation method that can significantly improve the piezoelectric properties of bismuth layered piezoelectric ceramics, which specifically comprises the following steps:

[0010] (1) According to (Bi2O2)(A m-1 B m O 3m+1 ) weighing oxides and / or carbonate raw materials of Bi, A and B elements in a stoichiometric ratio;

[0011] Wherein, A is selected from any one or more of Na, Li, Ca, Ce, Bi, Sr, K, Ba, Pb, La, Y, Gd, and Pr, B is selected from any one or more of Ti, Nb, W, and Ta, and m is a positive integer;

[0012] (2) subjecting the raw materials to ball milling, pretreatment, secondary ball milling, molding, binder removal, sintering, and then naturally cooling to room temperature to obtain a bismuth layered piezoelectric ceramic block;

[0013] Wherein, the sintering temperature is T1;

[0014] (3) placing the bismuth layered piezoelectric ceramic block obtained in step (2) in a mold cavity of a high-temperature resistant mold and heating it to T2;

[0015] Where T1 and T2 satisfy the following relationship: 0℃≤T1-T2≤200℃;

[0016] (4) maintaining the temperature T2 described in step (3), applying a constant pressure P to the bismuth layered piezoelectric ceramic block along its axial direction and maintaining it for a period of time t, and then naturally cooling it to room temperature after unloading the pressure to obtain a dense bismuth layered piezoelectric ceramic block with a textured microstructure;

[0017] According to some embodiments of the present invention, T1 satisfies the following relationship:

[0018] 1000℃≤T1≤1250℃;

[0019] According to some embodiments of the present invention, P satisfies the following relationship:

[0020] 15MPa≤P≤50MPa;

[0021] According to some embodiments of the present invention, t satisfies the following relationship:

[0022] 0.5h≤t≤2h;

[0023] According to some embodiments of the present invention, the mold cavity of the high temperature resistant mold is a high temperature alloy mold cavity, a silicon carbide mold cavity or an alumina mold cavity;

[0024] According to some embodiments of the present invention, in step (3), the specific operation of placing the bismuth layered piezoelectric ceramic block obtained in step (2) in the mold cavity of the high-temperature resistant mold is as follows: the bismuth layered piezoelectric ceramic block obtained in step (2) is isolated from the mold cavity of the high-temperature resistant mold, and from the upper and lower pressure rods with carbon paper with a thickness of 0.5 mm to 2 mm;

[0025] According to some embodiments of the present invention, in step (2), a gap of not less than 1 mm is provided between the outer surface of the bismuth layered piezoelectric ceramic block and the inner surface of the mold cavity of the high-temperature resistant mold;

[0026] According to some embodiments of the present invention, the method further comprises the following steps:

[0027] (5) cutting the dense bismuth layered piezoelectric ceramic block obtained in step (4) into dense bismuth layered piezoelectric ceramic sheets, heat-treating the dense bismuth layered piezoelectric ceramic sheets to expel carbon elements that have infiltrated into the dense bismuth layered piezoelectric ceramic sheets, and then forming metal electrodes on the upper and lower surfaces of the dense bismuth layered piezoelectric ceramic sheets. Then, applying a direct current electric field along the thickness direction of the dense bismuth layered piezoelectric ceramic sheets and polarizing them in a silicone oil bath;

[0028] wherein the thickness direction of the dense bismuth layered piezoelectric ceramic sheet is perpendicular to the direction of the pressure in step (4);

[0029] According to some embodiments of the present invention, the temperature of the silicone oil bath is not less than 180°C;

[0030] According to some embodiments of the present invention, the DC electric field strength is not less than 8 kV / mm;

[0031] According to some embodiments of the present invention, the heat treatment of the dense bismuth layered piezoelectric ceramic sheet in step (5) is specifically performed as follows: heat treatment at 800° C. to 1100° C. for 0.5 h to 2 h;

[0032] According to some embodiments of the present invention, the metal electrode in step (5) is a gold electrode, a silver electrode or a platinum electrode; the specific operation of making the metal electrodes on the upper and lower surfaces of the dense bismuth layered piezoelectric ceramic sheet in step (5) is:

[0033] After coating the metal slurry on the upper and lower surfaces of the ceramic sheet, the metal slurry is sintered at a temperature ranging from 450° C. to 1000° C. for 10 minutes to 30 minutes.

[0034] According to some embodiments of the present invention, step (2) of sequentially subjecting the raw materials to ball milling, pretreatment, secondary ball milling, molding, binder removal, sintering, and then naturally cooling to room temperature to obtain a bismuth layered piezoelectric ceramic block is specifically divided into the following steps:

[0035] (2.1) Ball milling: Pour the weighed raw materials from step (1) into a ball mill in sequence. Add anhydrous ethanol or deionized water as a ball milling dispersant, with the volume of the dispersant added being 2 / 3 of the ball mill volume. Use yttrium-stabilized zirconia balls as the ball milling medium, where the zirconium balls are arranged in a mass ratio of large: medium: small = 2:5:3, with the diameters of large, medium, and small zirconium balls being 10 mm, 8 mm, and 6 mm, respectively. Use planetary ball milling to uniformly mix the raw materials and refine the particle size. The ball milling speed is 200 rpm and the ball milling time is 12 h.

[0036] (2.2) Pretreatment: The obtained slurry was dried and placed in an alumina crucible and calcined at 850°C for 2 h;

[0037] (2.3) Secondary ball milling: The powder obtained in step (2.2) was ball milled again for 12 h according to the method of step (2.1);

[0038] (2.4) Molding: After drying the slurry obtained in step (2.3), a 12 wt% polyvinyl alcohol (PVA) solution was added and granulated; the resulting granules were pressed into rectangular green bodies or cylindrical green bodies;

[0039] (2.5) Debinding: The green body obtained in step (2.4) is burned at 200°C to 450°C to completely remove the PVA;

[0040] (2.6) Sintering: The green body obtained in step (2.5) was sintered at T1°C for 6 h and then naturally cooled to room temperature to obtain a bismuth layered piezoelectric ceramic block;

[0041] According to some embodiments of the present invention, the size of the cuboid green body in step (2.4) is: 12 mm × 12 mm × 20 mm;

[0042] According to some embodiments of the present invention, the dimensions of the cylindrical green body in step (2.4) are: 12 mm in diameter and 10 mm in height;

[0043] According to some embodiments of the present invention, the size of the dense bismuth layered piezoelectric ceramic sheet in step (5) is 5 mm × 5 mm × 0.6 mm;

[0044] According to some embodiments of the present invention, the sintering temperature T1 is 1000°C, 1010°C, 1020°C, 1030°C, 1040°C, 1050°C, 1060°C, 1070°C, 1080°C, 1090°C, 1100°C, 1110°C, 1120°C, 1130°C, 1140°C, 1150°C, 1160°C, 1170°C, 1180°C, 1190°C, 1200°C, 1210°C, 1220°C, 1230°C, 1240°C or 1250°C;

[0045] According to some embodiments of the present invention, the constant pressure P is 15 MPa, 20 MPa, 25 MPa, 30 MPa, 35 MPa, 40 MPa, 45 MPa or 50 MPa;

[0046] According to some embodiments of the present invention, the constant pressure maintaining time t is 0.5h, 1h, 1.5h or 2h.

[0047] Compared with the prior art, the present invention has the following characteristics and beneficial technical effects:

[0048] The preparation method of the present invention adds a pressurized heat treatment step after sintering the piezoelectric ceramic green body. Without changing the original formula, the bismuth layered piezoelectric ceramic block undergoes compression deformation, rearranges the grains, and partially grows in a preferred orientation, thereby obtaining a dense bismuth layered piezoelectric ceramic block with a textured microstructure. Compared with conventional sintered ceramics, the bismuth layered piezoelectric ceramic prepared by the present invention can significantly improve its piezoelectric performance due to its textured microstructure. The density ρ of the dense bismuth layered piezoelectric ceramic block is increased by 1.65% to 3.43%, and d 33 The improvement range is between 52.57% and 155.74%, and the dielectric constant ε r The improvement range is between 14.52% and 195.35%, which makes the bismuth layered piezoelectric ceramics prepared by the present invention more suitable for preparing sensitive piezoelectric elements of high-temperature piezoelectric sensors for vibration status monitoring of aircraft engines, gas turbines, and reactors. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 XRD patterns of the piezoelectric ceramic materials prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention;

[0050] Figure 2 SEM images of the piezoelectric ceramic materials prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention;

[0051] Figure 3 Depolarization spectra of the piezoelectric ceramic materials prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention;

[0052] Figure 4 The dielectric-temperature spectra of the piezoelectric ceramic materials prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention are shown. DETAILED DESCRIPTION

[0053] To make the technical problems solved by the present invention, the technical solutions adopted, and the technical effects achieved more clearly, the technical solutions of the embodiments of the present invention will be further described in detail below. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making any creative efforts shall fall within the scope of protection of the present invention.

[0054] It should be noted that references to "embodiments" herein mean that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of such phrases in various locations in the specification does not necessarily refer to the same embodiment, nor does it necessarily refer to independent or alternative embodiments that are mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0055] The experimental methods in the following examples are conventional methods unless otherwise specified. The materials and reagents used in the following examples are commercially available unless otherwise specified.

[0056] Example 1:

[0057] A preparation method capable of significantly improving the piezoelectric properties of bismuth layered piezoelectric ceramics, wherein the chemical formula of the bismuth layered piezoelectric ceramics is A = Ca, Na, Li, Ce, Bi, and B = Ta, i.e., its chemical formula is Ca 0.5 (NaBi) 0.23 (LiCe) 0.02 Bi2Ta2O9, the material is abbreviated as: CNLCBT(HF), where HF is the abbreviation of Hot Forging.

[0058] The preparation method of CNLCBT (HF) ceramics comprises the following steps:

[0059] (1) According to the chemical formula of CNLCBT (HF), various raw materials were weighed according to Table 1 (the weighing error was ±0.0005 g).

[0060] Table 1 CNLCBT (HF) ceramic ingredients

[0061]

[0062] (2) subjecting the raw materials to ball milling, pretreatment, secondary ball milling, molding, binder removal, sintering, and then naturally cooling to room temperature to obtain a bismuth layered piezoelectric ceramic block;

[0063] Step (2) is specifically divided into the following steps:

[0064] (2.1) Ball milling: Pour the weighed raw materials from step (1) into a ball mill in sequence. Add anhydrous ethanol or deionized water as a ball milling dispersant, with the volume of the dispersant added being 2 / 3 of the ball milling volume. Use yttrium-stabilized zirconia balls as the ball milling medium, where the zirconium balls are arranged in a mass ratio of large: medium: small = 2:5:3, with the diameters of large, medium, and small zirconium balls being 10 mm, 8 mm, and 6 mm, respectively. Use planetary ball milling to uniformly mix the raw materials and refine the particle size. The ball milling speed is 200 rpm and the ball milling time is 12 h.

[0065] (2.2) Pretreatment: The obtained slurry was dried and placed in an alumina crucible and calcined at 850°C for 2 h;

[0066] (2.3) Secondary ball milling: The powder obtained in step (2.2) was ball milled again for 12 h according to the method of step (2.1);

[0067] (2.4) Molding: After drying the slurry obtained in step (2.3), a 12 wt% polyvinyl alcohol (PVA) solution was added and granulated; the resulting granules were pressed into rectangular green bodies of 12 mm × 12 mm × 20 mm;

[0068] (2.5) Debinding: The green body obtained in step (2.4) is burned at 200°C to 450°C to completely remove the PVA;

[0069] (2.6) Sintering: The green body obtained in step (2.5) was sintered at T1 = 1200° C. for 6 h and then naturally cooled to room temperature to obtain a bismuth layered piezoelectric ceramic block;

[0070] (3) placing the bismuth layered piezoelectric ceramic block obtained in step (2) in a mold cavity of a high-temperature resistant aluminum oxide mold, with a gap of not less than 1 mm between the outer surface of the bismuth layered piezoelectric ceramic block and the inner surface of the mold cavity of the high-temperature resistant mold, and isolating the bismuth layered piezoelectric ceramic block from the mold cavity of the high-temperature resistant mold, and from the upper and lower pressure rods with carbon paper having a thickness of 0.5 mm to 2 mm; heating the block to T2 = 1180°C;

[0071] (4) maintaining the temperature of 1180° C. described in step (3), applying a constant pressure of 20 MPa to the bismuth layered piezoelectric ceramic block along its axial direction and maintaining the pressure for 2 h, and then naturally cooling the block to room temperature to obtain a dense bismuth layered piezoelectric ceramic block having a textured microstructure;

[0072] (5) Cutting the dense bismuth layered piezoelectric ceramic block obtained in step (4) into dense bismuth layered piezoelectric ceramic sheets, wherein the thickness direction of the dense bismuth layered piezoelectric ceramic sheets is perpendicular to the direction of the pressure in step (4), and heat-treating the dense bismuth layered piezoelectric ceramic sheets at 1000°C for 1 hour to expel the carbon elements that have infiltrated into the dense bismuth layered piezoelectric ceramic sheets; then applying silver paste printed by screen printing on the upper and lower surfaces of the ceramic sheets, calcining at 650°C for 15 minutes to make metal electrodes on the upper and lower surfaces of the dense bismuth layered piezoelectric ceramic sheets, and then applying a DC electric field with an intensity of 10 kV / mm along the thickness direction thereof, and polarizing in a silicone oil bath at a temperature of not less than 220°C for 20 minutes. Thus, a CNLCBT (HF) ceramic having significantly improved piezoelectric properties compared to conventional sintered ceramics can be obtained.

[0073] Example 2:

[0074] A preparation method capable of significantly improving the piezoelectric properties of bismuth layered piezoelectric ceramics, wherein the chemical formula of the bismuth layered piezoelectric ceramics is A = Ca, Sr, Bi, Li, Ce, and B = Nb, Ta, W, i.e., its chemical formula is Ca 0.775 Sr 0.025 (Li 0.5 Ce 0.15 Bi 0.35 ) 0.2 Bi2Nb 1.94 Ta 0.04 W 0.02 O9, the material abbreviation is: CSBN (HF).

[0075] The steps of the preparation method of CSBN (HF) ceramics are similar to those of Example 1, except that the ingredients are weighed according to Table 2, T1 = 1130°C, T2 = 1100°C, the heat treatment temperature for expelling the carbon element infiltrated into the dense bismuth layered piezoelectric ceramic sheet in step (5) is 900°C, and the polarization condition is a silicone oil bath temperature of not less than 200°C for polarization for 30 minutes, the other operations are the same as those of Example 1.

[0076] Table 2 CSBN (HF) ceramic ingredients

[0077]

[0078] Example 3:

[0079] A preparation method for significantly improving the piezoelectric properties of bismuth layered piezoelectric ceramics, wherein the chemical formula of the bismuth layered piezoelectric ceramics is A = Bi, Ce, B = Ti, Nb, Ta, W, that is, the chemical formula is Bi 2.95 Ce 0.05 (TiNb) 0.97 (WTa)0.03 O9, the material abbreviation is: BCTNTW (HF).

[0080] The steps of the preparation method of BCTNTW (HF) ceramics are similar to those of Example 1, except that the ingredients are weighed with reference to Table 3, T1 = 1130 ° C, T2 = 1080 ° C, the heat treatment temperature for expelling the carbon element infiltrated into the dense bismuth layered piezoelectric ceramic sheet in step (5) is 900 ° C, the time is 2 h, and the polarization conditions are a silicone oil bath temperature of not less than 200 ° C and polarization for 30 min, all other operations are the same as in Example 1.

[0081] Table 3 BCTNTW (HF) ceramic ingredients

[0082]

[0083] Example 4:

[0084] A preparation method can significantly improve the piezoelectric properties of bismuth layered piezoelectric ceramics, wherein the chemical formula of the bismuth layered piezoelectric ceramics is A=Ca, B=Nb, that is, its chemical formula is CaBi2Nb2O9, and the material is abbreviated as: CBN(HF).

[0085] The steps of the preparation method of CNB (HF) ceramics are similar to those of Example 1, except that the ingredients are weighed with reference to Table 4, T1 = 1130°C, T2 = 1080°C, the heat treatment temperature for expelling the carbon element infiltrated into the dense bismuth layered piezoelectric ceramic sheet in step (5) is 900°C, the time is 2h, and the polarization condition is a silicone oil bath temperature of not less than 200°C and polarization for 30min, all other operations are the same as those of Example 1.

[0086] Table 4 CBN (HF) ceramic ingredients

[0087]

[0088] Example 5:

[0089] A preparation method can significantly improve the piezoelectric properties of bismuth layered piezoelectric ceramics, wherein the chemical formula of the bismuth layered piezoelectric ceramics is A=Bi, B=Nb, Ti, that is, its chemical formula is Bi3TiNbO9, and the material is abbreviated as: BTN(HF).

[0090] The steps of the preparation method of BTN (HF) ceramics are similar to those of Example 1, except that the ingredients are weighed according to Table 3, T1 = 1130°C, T2 = 1100°C, the heat treatment temperature for expelling the carbon element infiltrated into the dense bismuth layered piezoelectric ceramic sheet in step (5) is 900°C, the time is 2h, and the polarization conditions are a silicone oil bath temperature of not less than 200°C and polarization for 30min, all other operations are the same as those of Example 1.

[0091] Table 5 BTN (HF) ceramic ingredients

[0092]

[0093] Examples 6-11

[0094] The ceramic components prepared in Examples 6-11 are the same as those in Example 1. Except that T2, P and t are not completely consistent, the rest of the preparation method is the same as that in Example 1. For the specific values of T2, P and t, please refer to the performance test results of Example 1 and Examples 6-11 in Table 10.

[0095] Comparative Examples 1-5

[0096] The ceramic components prepared in Comparative Examples 1-5 correspond one to one with those in Examples 1-5, and the preparation methods are also relatively similar, except that Comparative Examples 1-5 do not have steps (3)-(4) and there is no carbon removal step in step (5). That is, after completing step (2), the bismuth layered piezoelectric ceramic block prepared in step (2) is cut, electrodes are prepared, and polarization is performed.

[0097] Taking Comparative Example 1 as an example, the preparation method of bismuth layered piezoelectric ceramics, wherein the chemical formula of the bismuth layered piezoelectric ceramics is A=Ca, Na, Li, Ce, Bi, and B=Ta, that is, its chemical formula is Ca 0.5 (NaBi) 0.23 (LiCe) 0.02 Bi2Ta2O9, the material is abbreviated as: CNLCBT (CS), where CS is the abbreviation of Conventional Sintering.

[0098] The preparation method of CNLCBT (CS) ceramics includes the following steps:

[0099] (1) According to the chemical formula of CNLCBT (CS), various raw materials were weighed according to Table 6 (the weighing error was ±0.0005 g).

[0100] Table 6 CNLCBT (CS) ceramic ingredients

[0101]

[0102] (2) subjecting the raw materials to ball milling, pretreatment, secondary ball milling, molding, binder removal, sintering, and then naturally cooling to room temperature to obtain a bismuth layered piezoelectric ceramic block;

[0103] Step (2) is specifically divided into the following steps:

[0104] (2.1) Ball milling: Pour the weighed raw materials from step (1) into a ball mill in sequence. Add anhydrous ethanol or deionized water as a ball milling dispersant, with the volume of the dispersant added being 2 / 3 of the ball milling volume. Use yttrium-stabilized zirconia balls as the ball milling medium, where the zirconium balls are arranged in a mass ratio of large: medium: small = 2:5:3, with the diameters of large, medium, and small zirconium balls being 10 mm, 8 mm, and 6 mm, respectively. Use planetary ball milling to uniformly mix the raw materials and refine the particle size. The ball milling speed is 200 rpm and the ball milling time is 12 h.

[0105] (2.2) Pretreatment: The obtained slurry was dried and placed in an alumina crucible and calcined at 850°C for 2 h;

[0106] (2.3) Secondary ball milling: The powder obtained in step (2.2) was ball milled again for 12 h according to the method of step (2.1);

[0107] (2.4) Molding: After drying the slurry obtained in step (2.3), a 12 wt% polyvinyl alcohol (PVA) solution was added and granulated; the resulting granules were pressed into rectangular green bodies of 12 mm × 12 mm × 20 mm;

[0108] (2.5) Debinding: The green body obtained in step (2.4) is burned at 200°C to 450°C to completely remove the PVA;

[0109] (2.6) Sintering: The green body obtained in step (2.5) was sintered at T1 = 1200° C. for 6 h and then naturally cooled to room temperature to obtain a bismuth layered piezoelectric ceramic block;

[0110] (5) Cutting the bismuth layered piezoelectric ceramic block obtained in step (2.6) into thin slices, wherein the thickness direction of the thin slice is perpendicular to the direction of the forming pressure in (2.4); then screen-printing silver paste on the upper and lower surfaces of the ceramic slices, calcining at 650°C for 15 minutes to form metal electrodes on the upper and lower surfaces of the bismuth layered piezoelectric ceramic slices; then applying a DC electric field with an intensity of 10 kV / mm along the thickness direction thereof, and polarizing in a silicone oil bath at a temperature of not less than 220°C for 20 minutes. Conventionally sintered CNLCBT (CS) ceramics are thus obtained.

[0111] Correspondingly, the materials of Comparative Examples 2-5 are abbreviated as CSBN (CS), BCTNTW (CS), CBN (CS) and BTN (CS) respectively.

[0112] Comparative Examples 6-8

[0113] The ceramic components prepared in Comparative Examples 6-8 correspond to those in Examples 1-3, and the preparation methods are also similar. Except that Comparative Examples 6-8 do not have step (2.6) of sintering at temperature T1, the others are the same as the corresponding examples.

[0114] Taking Comparative Example 6 as an example, a preparation method of a bismuth layered piezoelectric ceramic is a preparation method that can significantly improve the piezoelectric properties of the bismuth layered piezoelectric ceramic, and the material is abbreviated as: CNLCBT(HF)'.

[0115] The preparation method of CNLCBT(HF)' ceramics includes the following steps:

[0116] (1) According to the chemical formula of CNLCBT (HF), various raw materials were weighed according to Table 1 (the weighing error was ±0.0005 g).

[0117] (2) subjecting the raw materials to ball milling, pretreatment, secondary ball milling, molding, binder removal, sintering, and then naturally cooling to room temperature to obtain a bismuth layered piezoelectric ceramic block;

[0118] Step (2) is specifically divided into the following steps:

[0119] (2.1) Ball milling: Pour the weighed raw materials from step (1) into a ball mill in sequence. Add anhydrous ethanol or deionized water as a ball milling dispersant, with the volume of the dispersant added being 2 / 3 of the ball milling volume. Use yttrium-stabilized zirconia balls as the ball milling medium, where the zirconium balls are arranged in a mass ratio of large: medium: small = 2:5:3, with the diameters of large, medium, and small zirconium balls being 10 mm, 8 mm, and 6 mm, respectively. Use planetary ball milling to uniformly mix the raw materials and refine the particle size. The ball milling speed is 200 rpm and the ball milling time is 12 h.

[0120] (2.2) Pretreatment: The obtained slurry was dried and placed in an alumina crucible and calcined at 850°C for 2 h;

[0121] (2.3) Secondary ball milling: The powder obtained in step (2.2) was ball milled again for 12 h according to the method of step (2.1);

[0122] (2.4) Molding: After drying the slurry obtained in step (2.3), a 12 wt% polyvinyl alcohol (PVA) solution was added and granulated; the resulting granules were pressed into rectangular green bodies of 12 mm × 12 mm × 20 mm;

[0123] (2.5) Debinding: The green body obtained in step (2.4) is burned at 200°C to 450°C to completely remove the PVA;

[0124] (3) placing the bismuth layered piezoelectric ceramic green body obtained in step (2) in a mold cavity of a high-temperature resistant aluminum oxide mold, with a gap of not less than 1 mm between the outer surface of the bismuth layered piezoelectric ceramic green body and the inner surface of the mold cavity of the high-temperature resistant mold, and isolating the upper and lower surfaces of the bismuth layered piezoelectric ceramic block from the mold cavity of the high-temperature resistant mold and from the upper and lower pressure rods with carbon paper having a thickness of 0.5 mm to 2 mm; heating the green body to T2 = 1180°C;

[0125] (4) maintaining the temperature of 1180° C. described in step (3), applying a constant pressure of 20 MPa to the bismuth layered piezoelectric ceramic block along its axial direction and maintaining the pressure for 2 h, and then naturally cooling the block to room temperature to obtain a dense bismuth layered piezoelectric ceramic block having a textured microstructure;

[0126] (5) Cutting the dense bismuth layered piezoelectric ceramic block obtained in step (4) into dense bismuth layered piezoelectric ceramic sheets, wherein the thickness direction of the dense bismuth layered piezoelectric ceramic sheets is perpendicular to the direction of the pressure in step (3), and heat-treating the dense bismuth layered piezoelectric ceramic sheets at 1000°C for 1 hour to expel the carbon elements that have infiltrated into the dense bismuth layered piezoelectric ceramic sheets; then applying silver paste printed by screen printing on the upper and lower surfaces of the ceramic sheets, calcining at 650°C for 15 minutes to make metal electrodes on the upper and lower surfaces of the dense bismuth layered piezoelectric ceramic sheets, and then applying a DC electric field with an intensity of 10 kV / mm along the thickness direction thereof, and polarizing in a silicone oil bath at a temperature not lower than 220°C for 20 minutes. CNLCBT(HF)' ceramics can be obtained.

[0127] Correspondingly, the materials of Comparative Examples 7-8 are respectively abbreviated as CSBN(HF)' and BCTNTW(HF)'.

[0128] Experiments, testing and raw material sources

[0129] Table 7 Performance of Examples 1-5 and Comparative Examples 1-5 Raw material purity and source manufacturers

[0130]

[0131] Table 8 Related equipment in the preparation process of Examples 1-5 and Comparative Examples 1-5

[0132]

[0133] Test methods and equipment used:

[0134] (1) Density ρ test method and equipment: Based on the principle of Archimedes displacement, the buoyancy of an object when immersed in water is equal to the weight of the water it displaces. By measuring the mass difference between the ceramic sample in air and water, the volume is calculated, and then the density is obtained. The density of water at room temperature is ρ水 =1g / cm 3 First, ensure that the sample surface is clean and dry, and then use an electronic balance (Sartorius BSA224S) to weigh the mass of the sample when it is dry to obtain the dry weight m 干 (In order to reduce the error, the number of samples should usually be greater than 3), and then the dry sample is suspended and immersed in a beaker filled with water to weigh the mass to obtain the wet weight m 湿 Finally, the density of the sample is calculated using the density formula: Finally, the average value of the density of multiple samples is taken as the final result.

[0135] (2)d 33 Test method and equipment: The quasi-static method is based on the direct piezoelectric effect. By applying a low-frequency alternating force (usually below the resonant frequency) to the piezoelectric ceramic sample, the ratio of the generated charge Q to the applied force F is measured, and d is calculated. 33 After the surface of the ceramic sample coated with electrodes is polarized under a DC electric field, it is placed in air for 24 hours to eliminate the residual charge. The polarized ceramic piece is clamped in a quasi-static 33 The tester (ZJ-6A, Institute of Acoustics, Chinese Academy of Sciences) is installed and ensures good contact with the test probe. The static holding force is controlled by the motor switch to ensure contact stability. The electromagnetic driver applies a sinusoidal alternating force to trigger the piezoelectric effect, and finally displays d 33 At least three samples were measured for each group and the average value was taken to reduce the discreteness.

[0136] (3) Dielectric constant ε r Test method and equipment: By measuring the capacitance value C of the ceramic sample under the alternating electric field, combined with the geometric dimensions of the sample (area A, thickness d), the dielectric constant ε is calculated. r , the calculation formula is: where ε0 = 8.854 × 10 -12 F / m is the vacuum dielectric constant. A ceramic sample coated with electrodes was tested in an LCR meter (Hioki, IM3536) at a voltage of 1 V and a frequency of 1 kHz. The capacitance of the sample was measured, and the dielectric constant was calculated using the above formula.

[0137] Tables 9-11 are the performance test results of various embodiments and comparative examples, where the definition of the "increase" of each parameter is as follows: for bismuth layered piezoelectric ceramics of the same component, reference is made to the performance test results of comparative examples 1-5, such as embodiments 1, 6-11, and comparative example 6, the increase of each parameter is calculated relative to the corresponding parameter of comparative example 1; the increase of each parameter of embodiment 2 and comparative example 7 is calculated relative to the corresponding parameter of comparative example 2; the increase of each parameter of embodiment 3 and comparative example 8 is calculated relative to the corresponding parameter of comparative example 3; the increase of each parameter of embodiment 4 is calculated relative to the corresponding parameter of comparative example 4; the increase of each parameter of embodiment 5 is calculated relative to the corresponding parameter of comparative example 5.

[0138] The specific calculation formula takes the density ρ of Example 1 as an example:

[0139] Table 9 Performance test results of Examples 1-5 and Comparative Examples 1-5

[0140]

[0141]

[0142] Table 10 Performance test results of Example 1 and Examples 6-11

[0143]

[0144] Table 11 Performance test results of Examples 1-3 and Comparative Examples 6-8

[0145]

[0146] Test result analysis:

[0147] pass Figure 1 The ceramics of Examples 1-3 and Comparative Examples 1-3 are single bismuth layered structures, which correspond well to the theoretical peak of the orthorhombic A21am phase and do not contain a second phase. Figure 2 The SEM images show that the density of Examples 1-3 is higher than that of Comparative Examples 1-3. Figure 3 Depolarization and Figure 4 It can be seen from the dielectric constant and d of Examples 1-3 that 33 Both have been significantly improved, and similar conclusions can be drawn by combining the data of Examples 4-5 and Comparative Examples 4-5 in Table 9. This is mainly because the present invention adds a step after the conventional solid-phase sintering process to form the bismuth layered piezoelectric ceramic block: namely, applying a certain pressure for a period of time at a temperature within 200°C below the sintering temperature to cause the bismuth layered piezoelectric ceramic block to undergo compression deformation, rearrange the grains, and partially grow in a preferred orientation, thereby obtaining a dense bismuth layered piezoelectric ceramic block with a textured microstructure.

[0148] From Table 10 and the comparison between Example 1 and Examples 6-11, it can be seen that since T1 is the conventional sintering temperature of ceramics, the difference mainly depends on the ceramic system. When bismuth layered ceramics are prepared under the conditions of 0℃≤T1-T2≤200℃, 15MPa≤P≤50MPa and 0.5h≤t≤2h, the piezoelectric activity of the ceramic can be greatly improved.

[0149] From the comparison of Table 11 and Comparative Examples 6-8, it can be seen that the effect of pressure sintering alone is not ideal. The main reason is that the green body after debinding has not been pre-sintered. When the heating temperature reaches T2, under the action of pressure, the green body after debinding has not been pre-sintered, and the grains are small. When pressure is applied at the T2 temperature, although the green body can be compressed, the grains cannot achieve the purpose of turning and rearranging during the compression of the green body, and under the action of pressure, the grain growth will also be inhibited to a certain extent; on the other hand, due to the poor strength of the green body, it is internally broken, and the final sample is often accompanied by large cracks inside, so its performance is not significantly improved and some are even reduced.

[0150] The above detailed description of a method for preparing bismuth layered piezoelectric ceramics that significantly improves the piezoelectric properties of these ceramics is intended to further illustrate the present invention in conjunction with specific preferred embodiments. The present invention should not be construed as being limited to these specific descriptions. Those skilled in the art will appreciate the flexibility and adaptability of the present invention's design, allowing for the development of a range of products without departing from the present invention. Simple deductions or substitutions should be considered within the scope of the present invention as defined by the submitted claims.

Claims

1. A preparation method capable of significantly improving the piezoelectric properties of bismuth layered piezoelectric ceramics, characterized in that: The following steps are involved: (1) According to (Bi2O2)(A m-1 B m O 3m+1 ) weigh analytically pure oxides and / or carbonate raw materials of Bi, A and B elements in a stoichiometric ratio; Wherein, A is selected from any one or more of Na, Li, Ca, Ce, Bi, Sr, K, Ba, Pb, La, Y, Gd, and Pr, B is selected from any one or more of Ti, Nb, W, and Ta, and m is a positive integer; (2) subjecting the raw materials to ball milling, pretreatment, secondary ball milling, molding, binder removal, sintering, and then naturally cooling to room temperature to obtain a bismuth layered piezoelectric ceramic block; wherein the sintering temperature is T1; (3) placing the bismuth layered piezoelectric ceramic block in a mold cavity of a high-temperature resistant mold and heating it to T2; Where T1 and T2 satisfy the following relationship: 0℃≤T1-T2≤200℃; (4) maintaining the temperature T2 described in step (3), applying a constant pressure P to the bismuth layered piezoelectric ceramic block along its axial direction and maintaining it for a period of time t, and then naturally cooling it to room temperature after unloading the pressure to obtain a dense bismuth layered piezoelectric ceramic block with a textured microstructure.

2. The method for preparing a bismuth layered piezoelectric ceramic capable of significantly improving its piezoelectric properties according to claim 1, characterized in that: T1 satisfies the following relationship: 1000°C≤T1≤1250°C.

3. The method for preparing a bismuth layered piezoelectric ceramic capable of significantly improving its piezoelectric properties according to claim 1, characterized in that: P satisfies the following relationship: 15MPa≤P≤50MPa; t satisfies the following relationship: 0.5h≤t≤2h.

4. The method for preparing a bismuth layered piezoelectric ceramic capable of significantly improving its piezoelectric properties according to claim 1, wherein: The mold cavity of the high temperature resistant mold is a high temperature alloy mold cavity, a silicon carbide mold cavity or an aluminum oxide mold cavity.

5. The method for preparing a bismuth layered piezoelectric ceramic capable of significantly improving its piezoelectric properties according to any one of claims 1 to 4, characterized in that: In the step (3), the specific operation of placing the bismuth layered piezoelectric ceramic block in the mold cavity of the high-temperature resistant mold is: the upper and lower surfaces of the bismuth layered piezoelectric ceramic block obtained in step (2) are isolated from the mold cavity of the high-temperature resistant mold and from the upper and lower pressure rods using carbon paper with a thickness of 0.5 mm to 2 mm.

6. The method for preparing a bismuth layered piezoelectric ceramic capable of significantly improving its piezoelectric properties according to claim 5, characterized in that: In the step (2), a gap of not less than 1 mm is provided between the outer surface of the bismuth layered piezoelectric ceramic block and the inner surface of the mold cavity of the high-temperature resistant mold.

7. The method for preparing a bismuth layered piezoelectric ceramic capable of significantly improving its piezoelectric properties according to any one of claims 1 to 4, characterized in that: The method further comprises the following steps: (5) cutting the dense bismuth layered piezoelectric ceramic block obtained in step (4) into dense bismuth layered piezoelectric ceramic sheets, heat-treating the dense bismuth layered piezoelectric ceramic sheets to expel carbon elements that have infiltrated into the dense bismuth layered piezoelectric ceramic sheets, and then forming metal electrodes on the upper and lower surfaces of the dense bismuth layered piezoelectric ceramic sheets. Then, applying a direct current electric field along the thickness direction of the dense bismuth layered piezoelectric ceramic sheets and polarizing them in a silicone oil bath; The thickness direction of the dense bismuth layered piezoelectric ceramic sheet is perpendicular to the direction of the pressure in step (4).

8. The method for preparing a bismuth layered piezoelectric ceramic capable of significantly improving its piezoelectric properties according to claim 7, characterized in that: The temperature of the silicone oil bath is not less than 180°C; The DC electric field strength is not less than 8kV / mm.

9. The method for preparing bismuth layered piezoelectric ceramics capable of significantly improving piezoelectric properties according to claim 8, characterized in that: The specific operation of heat treating the dense bismuth layered piezoelectric ceramic sheet in step (5) is as follows: Heat treatment at 800℃~1100℃ for 0.5h~2h.

10. The method for preparing bismuth layered piezoelectric ceramics capable of significantly improving piezoelectric properties according to claim 9, characterized in that: The metal electrode in step (5) is a gold electrode, a silver electrode or a platinum electrode; the specific operation of making the metal electrodes on the upper and lower surfaces of the dense bismuth layered piezoelectric ceramic sheet in step (5) is: After coating the metal slurry on the upper and lower surfaces of the ceramic sheet, the metal slurry is sintered at a temperature ranging from 450° C. to 1000° C. for 10 minutes to 30 minutes.

Images