A piezoelectric ceramic with high mechanical quality factor and aging resistance and its preparation method

Abstract

The present invention discloses a piezoelectric ceramic with high mechanical quality factor and high temperature aging resistance and a preparation method thereof, belonging to the technical field of piezoelectric ceramics. The chemical formula of the piezoelectric ceramic with high mechanical quality factor and high temperature aging resistance is (Bi 0.5 Na 0.44 K 0.04 Li 0.02 )(Ti 1‑x Co x )O3,0.01

Description

Technical Field

[0001] The present invention relates to the technical field of piezoelectric ceramics, and in particular to a piezoelectric ceramic with a high mechanical quality factor and high-temperature aging resistance and a preparation method thereof. Background Art

[0002] Piezoelectric ceramics are a class of functional materials that enable the conversion of electrical energy into mechanical energy and vice versa. They are widely used in fields such as information technology, optoelectronics, precision control, and nondestructive testing. These materials, through their mechanical and electrical properties, as well as their combined acoustic, optical, and thermal sensitivity, have enabled the development and application of a variety of devices, including piezoelectric resonators, piezoelectric buzzers, piezoelectric filters, piezoelectric transformers, piezoelectric speakers, piezoelectric igniters, and piezoelectric motors. With the rapid development of next-generation information technology and artificial intelligence, the application areas of piezoelectric ceramics are continuously expanding, and improving their performance and exploring new applications have become hot research topics.

[0003] In the study of piezoelectric ceramics, the mechanical quality factor (Q m ) is a key parameter that reflects the energy loss of the material during mechanical vibration and is particularly important for high power applications. m A high value means that the material has lower energy loss when vibrating, so it can convert electrical energy and mechanical energy more efficiently, reduce energy loss in the form of heat, and thus improve the efficiency and performance of the device.

[0004] Compared with traditional lead-containing piezoelectric ceramics (represented by Pb(Zr,Ti)O3), which bring serious harm to the environment and humans during production, use and disposal. 0.5 Na 0.5 TiO3, referred to as BNT), is a high-performance lead-free piezoelectric ceramic material that has attracted much attention due to its excellent piezoelectric properties and environmental friendliness. According to the latest research progress, the Q of BNT-based ceramics m The level has been significantly improved. For example, by Mn doping and optimizing the sintering process, the Q of BNT-based ceramics has been improved. m It can reach about 970, which is comparable to the Q of some commercial PZT ceramics. m In addition, BNT-based ceramics exhibit excellent Q at high vibration speeds. m The stability of BNTs indicates that they have great potential for high-power applications. The study also showed that the Q can be significantly improved by introducing other perovskite phases (such as BLT, BKT and BT) to form solid solutions with BNTs. m value and remain stable at high vibration speeds.

[0005] However, BNT-based ceramics have complex phase transitions and their piezoelectric properties (including Q m ) will be affected by the depolarization temperature Td (i.e., the ferroelectric-relaxation phase transition temperature T F-R ), temperature stability has become the key to restricting practical applications; and long-term high temperature exposure will significantly accelerate the degradation of the electrical properties of piezoelectric ceramics, greatly affecting their service life. Summary of the Invention

[0006] The purpose of the present invention is to provide a piezoelectric ceramic with a high mechanical quality factor and high temperature aging resistance and a preparation method, so as to solve the problem that the existing sodium bismuth titanate-based piezoelectric ceramics are severely aged at high temperatures and affect the stability of the piezoelectric ceramics, and obtain sodium bismuth titanate-based piezoelectric ceramics with a high mechanical quality factor.

[0007] To achieve the above object, the present invention provides a piezoelectric ceramic with high mechanical quality factor and high temperature aging resistance, the chemical formula of the piezoelectric ceramic is (Bi 0.5 Na 0.44 K 0.04 Li 0.02 )(Ti 1-x Co x )O3,0.01 <x<0.03。

[0008] Preferably, the chemical formula of the piezoelectric ceramic is (Bi 0.5 Na 0.44 K 0.04 Li 0.02 )(Ti 0.977 Co 0.023 )O3.

[0009] The method for preparing the piezoelectric ceramic with high mechanical quality factor and high temperature aging resistance comprises the following steps:

[0010] S1. Weigh analytically pure sodium carbonate Na2CO3, potassium carbonate K2CO3, lithium carbonate LiCO3, bismuth trioxide Bi2O3, titanium dioxide TiO2, and cobalt trioxide Co2O3 according to molar percentage as raw materials, and ball-mill the raw materials to obtain a primary powder;

[0011] S2, drying the primary powder to obtain a uniformly mixed primary powder;

[0012] S3, pre-calcining the primary powder to obtain dry powder;

[0013] S4, performing secondary ball milling on the dry powder to obtain secondary powder;

[0014] S5, drying the secondary powder to obtain a uniformly mixed secondary powder;

[0015] S6. Adding a polyvinyl alcohol aqueous solution to the secondary powder and sequentially performing granulation, sieving, pressing and debinding to obtain a ceramic body;

[0016] S7, sintering the ceramic body to obtain a piezoelectric ceramic body;

[0017] S8. Silver electrodes are placed on the piezoelectric ceramic body and voltage is applied for polarization.

[0018] Preferably, in S1, the primary ball milling medium is anhydrous ethanol, the primary ball milling is a planetary ball mill, the ball milling jar is a nylon jar, the grinding balls are zirconium balls, and the primary ball milling time is 6 hours to 10 hours.

[0019] Preferably, in S3, the powder is pre-fired in a corundum crucible at a temperature of 800° C. to 900° C. for a time of 5 to 8 hours.

[0020] Preferably, in S4, the ball milling medium for the secondary ball milling is anhydrous ethanol, and the ball milling time for the secondary ball milling is 6 hours to 10 hours.

[0021] Preferably, in S6, a polyvinyl alcohol aqueous solution with a mass percentage of 6 wt% to 8 wt% is added to the secondary powder, and the screen mesh is 120 mesh; the secondary powder is pressed into round tablets using a manual tablet press, and the pressure of the manual tablet press is 8 MPa.

[0022] Preferably, in S7, the sintering temperature is 1100° C. to 1150° C., and the sintering time is 1 hour to 3 hours.

[0023] Preferably, in S8, the polarization voltage of the piezoelectric ceramic body is 4 kV / cm to 5 kV / cm, and the polarization time is 20 minutes to 40 minutes.

[0024] The piezoelectric coefficient d of the piezoelectric ceramic prepared by the above preparation method is 33 72pC / N~75pC / N, mechanical quality factor Q m The electromechanical coupling coefficient k is 482~730. p is 18% to 19%, and the dielectric constant ε r The dielectric loss tanδ is 362~469, the dielectric loss tanδ is 1.43%~2.74%, and it has good aging resistance at a high temperature of 150℃.

[0025] The advantages and positive effects of the piezoelectric ceramics with high mechanical quality factor and high temperature aging resistance and the preparation method of the present invention are:

[0026] 1. The present invention adopts Co2O3 doping BNT-based piezoelectric ceramics. Doping Co2O3 can compensate for the volatilization of elements at high temperatures, help improve the density of ceramics, and obtain high-quality piezoelectric ceramics. Co2O3 is used as an acceptor dopant. 2+ and Co 3+ Enter Ti 4+lattice sites, thereby forming an acceptor-defect dipole, which clamps the domain wall and stabilizes the domain, reducing dielectric loss and mechanical loss, and increasing Q m In addition, the defect dipole can be stably polarized at a high temperature of 150°C, improving the aging resistance of the piezoelectric ceramic.

[0027] 2. The preparation method of the present invention is simple in process, easy to operate, and convenient for industrial production. It can improve the mechanical quality factor Q of piezoelectric ceramic materials. m and aging resistance.

[0028] 3. The piezoelectric coefficient d of the piezoelectric ceramic prepared by the preparation method of the present invention 33 72pC / N~75pC / N, mechanical quality factor Q m The electromechanical coupling coefficient k is 482~730. p is 18% to 19%, and the dielectric constant ε r The dielectric loss tanδ is 362-469, the dielectric loss tanδ is 1.43%-2.74%, and it maintains excellent aging resistance at 150°C.

[0029] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a flow chart of the preparation method according to an embodiment of the present invention;

[0031] Figure 2 X-ray diffraction patterns of the piezoelectric ceramics prepared in Examples 1-3 of the present invention;

[0032] Figure 3 Schematic diagram of the relative dielectric constant and dielectric loss of the piezoelectric ceramics prepared in Examples 1-3 of the present invention changing with temperature at 100 kHz;

[0033] Figure 4 This is an impedance diagram of the piezoelectric ceramic prepared in Example 2 of the present invention;

[0034] Figure 5 Schematic diagram of the aging of the mechanical quality factor of the piezoelectric ceramics prepared in Examples 1-3 of the present invention at 150 degrees Celsius over time;

[0035] Figure 6 Schematic diagram of the aging of the electromechanical coupling coefficient of the piezoelectric ceramics prepared in Examples 1-3 of the present invention at 150 degrees Celsius over time;

[0036] Figure 7 Schematic diagram of the aging of the piezoelectric constant of the piezoelectric ceramics prepared in Examples 1-3 of the present invention at 150 degrees Celsius over time. DETAILED DESCRIPTION

[0037] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0038] A high mechanical quality factor, high temperature aging resistant base piezoelectric ceramic, the chemical formula is (Bi 0.5 Na 0.44 K 0.04 Li 0.02 )(Ti 1-x Co x )O3,0.01 <x<0.03。

[0039] The present invention uses Co2O3 as an acceptor dopant, which can enter the lattice to form defect dipoles, reduce the sintering temperature, help improve the density of the ceramic, and obtain high-quality piezoelectric ceramics. 2+ and Co 3+ Enter Ti 4+ lattice sites, thereby forming an acceptor-defect dipole, which clamps the domain wall and stabilizes the domain, reducing dielectric loss and mechanical loss, and increasing Q m In addition, the defect dipole can be stably polarized at a high temperature of 150°C, improving the aging resistance of the piezoelectric ceramic.

[0040] The molar ratio of doped Co2O3 is 0.023. When the ratio deviates from this, the phase structure of the ceramic will change significantly, and the impurity phase will cause the performance of the piezoelectric ceramic to deteriorate. 0.977 Co 0.023 "The atomic ratio of Ti and Co elements in the piezoelectric ceramic material needs to be 0.977 and 0.023. When the ratio changes, the defects will change accordingly, resulting in a decrease in its piezoelectric performance. When the ratio of the piezoelectric ceramic material is not within the range of molar ratio and atomic ratio, the addition of too little Co element is insufficient to form defect dipoles, while the addition of excessive Co element is limited by solid solubility and easily forms an impurity phase retained in the piezoelectric ceramic structure, resulting in a decrease in piezoelectric performance.

[0041] like Figure 1 As shown. A method for preparing a piezoelectric ceramic with a high mechanical quality factor and high temperature aging resistance comprises the following steps:

[0042] S1. Weigh analytically pure sodium carbonate Na2CO3, potassium carbonate K2CO3, lithium carbonate LiCO3, bismuth trioxide Bi2O3, titanium dioxide TiO2, and cobalt trioxide Co2O3 according to molar percentage as raw materials, and ball-mill the raw materials once to obtain a powder.

[0043] The primary milling medium is anhydrous ethanol, the primary milling is a planetary ball mill, the primary milling jar is a nylon jar, the milling balls are zirconium balls, and the primary milling time is 6 to 10 hours, preferably 8 hours.

[0044] S2. Drying the primary powder to obtain a uniformly mixed primary powder.

[0045] S3. Pre-burning the primary powder to obtain dry powder.

[0046] The powder is pre-fired in a corundum crucible at a temperature of 800° C. to 900° C., preferably 850° C. The preferred pre-fire time is 6 hours.

[0047] S4. Ball milling the dry powder for the second time to obtain secondary powder.

[0048] The secondary ball milling medium is anhydrous ethanol, and the secondary ball milling time is 6 to 10 hours, preferably 8 hours. The secondary ball milling also uses zirconium balls to perform planetary ball milling in a nylon jar.

[0049] S5. Dry the secondary powder to obtain a uniformly mixed secondary powder.

[0050] S6. Adding polyvinyl alcohol aqueous solution to the secondary powder and sequentially performing granulation, sieving, pressing and debinding to obtain a ceramic body.

[0051] Add 6-8 wt% of polyvinyl alcohol aqueous solution to the secondary powder. If the polyvinyl alcohol aqueous solution concentration is less than 6 wt%, the sample may not form properly, and the piezoelectric ceramic material cannot be obtained. If the concentration is greater than 8 wt%, the piezoelectric performance may be reduced or the sample may contain pores, making it impossible to obtain a dense piezoelectric ceramic material. The polyvinyl alcohol aqueous solution content is preferably 7 wt%.

[0052] The mesh size of the sieve is 120. The secondary powder is pressed into round tablets using a manual tablet press at a pressure of 8 MPa.

[0053] S7. Sintering the ceramic body to obtain a piezoelectric ceramic body.

[0054] The sintering temperature is 1100° C. to 1150° C., and the sintering time is 1 hour to 3 hours.

[0055] S8. Silver electrodes are placed on the piezoelectric ceramic body and voltage is applied for polarization.

[0056] The polarization voltage of the piezoelectric ceramic body is 4 kV / cm to 5 kV / cm, and the polarization time is 20 minutes to 40 minutes.

[0057] Example 1

[0058] The general chemical formula of piezoelectric ceramics with high mechanical quality factor and high temperature aging resistance is:

[0059] (Bi 0.5 Na 0.44 K 0.04 Li 0.02)(Ti 0.985 Co 0.015 )O3.

[0060] Analytically pure Na2CO3, K2CO3, LiCO3, Bi2O3, TiO2, and Co2O3 were used as raw materials, and each raw material was accurately weighed in molar percentage. The weighed raw materials were ball-milled using anhydrous ethanol as the ball milling medium, followed by planetary ball milling for 8 hours, and then dried to obtain a mixed dry powder. The resulting dry powder was pre-calcined at 850°C for 6 hours. The pre-calcined powder was placed in a ball mill, ball-milled using anhydrous ethanol as the ball milling medium, and then planetary ball milled for 8 hours to obtain a secondary powder. A 7wt% aqueous solution of polyvinyl alcohol was added to the secondary powder to form granules, which were then sieved using a 120-mesh sieve. After sieving, the fine powder was pressed into small discs using a 10mm diameter mold under a pressure of 8MPa. The discs had a diameter of 10mm and a thickness of 0.8mm. The discs were debinded to obtain piezoelectric ceramic green bodies. The debinded discs were sintered at 1130°C for 2 hours to obtain piezoelectric ceramic green bodies. The sintered piezoelectric ceramic sheet was coated with silver electrodes and polarized in 95° C. silicone oil at a voltage of 5 kV / mm for 30 minutes.

[0061] After the polarized ceramic sheet was left to stand in air for 24 hours, the electrical properties were tested using the IEEE standard.

[0062] Example 2

[0063] The difference between this embodiment and embodiment 1 is that the piezoelectric ceramic chemical formula is:

[0064] (Bi 0.5 Na 0.44 K 0.04 Li 0.02 )(Ti 0.977 Co 0.023 )O3.

[0065] Example 3

[0066] The difference between this embodiment and embodiment 1 is that the piezoelectric ceramic chemical formula is:

[0067] (Bi 0.5 Na 0.44 K 0.04 Li 0.02 )(Ti 0.975 Co 0.025 )O3.

[0068] The piezoelectric ceramics obtained in Examples 1-3 were subjected to X-ray diffraction analysis, and the results were as follows: Figure 2As shown in the figure, there are eight characteristic peaks between 20 and 80°, which are

[100] ,

[110] ,

[111] ,

[200] ,

[210] ,

[211] ,

[220] , and

[310] as the angle increases, indicating that the ceramic material is a perovskite ceramic. This indicates that the heterogeneous element Co introduced by doping Co2O3 enters the matrix to form a solid solution, effectively improving the density of the ceramic. However, when the doping level is too high, a small amount of impurity phase is generated.

[0069] Figure 3 Schematic diagram of the relative dielectric constant and dielectric loss of the piezoelectric ceramic material described in Examples 1-3 of the present invention changing with temperature at 100kHz. Figure 3 As shown, the relative dielectric constant ε of the piezoelectric ceramic material r Two dielectric anomaly peaks appear with temperature change. Figure 1 T d (corresponding to the peak dielectric loss) and Figure 2 Corresponding T m (corresponding to the peak dielectric constant). d As the temperature increases, the state of the ferroelectric domain changes, and the directional dipoles are rearranged, resulting in a transition from the ferroelectric phase to the relaxation phase. The position of the first peak from low to high temperature is the dielectric anomaly peak at the dielectric loss peak, and the depolarization temperature T is measured here. d The second peak is the dielectric anomaly peak at the dielectric constant peak, where the Curie temperature T is measured. m is 284℃. Figure 1 It can be seen that with the increase of doping amount, T d First increase and then decrease. Figure 2 It can be seen that with the increase of doping amount, T m The dielectric loss reaches its minimum value when the doping amount x=0.023, and the maximum Q is also achieved at this time. m .

[0070] Figure 4 This is the impedance diagram of the piezoelectric ceramic material prepared in Example 2 of the present invention. Figure 4 As shown, the impedance shows a sharp resonance peak as the frequency changes, and the maximum phase angle is 79.1°, indicating that the mechanical quality factor of the ceramic is good at this time. m It is 730.

[0071] Figure 5 、 Figure 6 and Figure 7 The mechanical quality factors Q of Examples 1-3 of the present invention at 150°C are respectively m , electromechanical coupling coefficient k p and the piezoelectric constant d 33 Schematic diagram of aging over time. The mechanical quality factor Q is measured every 12 hours.m , electromechanical coupling coefficient k p and the piezoelectric constant d 33 .like Figure 5 、 Figure 6 and Figure 7 As shown in the figure, after 7 days of aging, the performance of Examples 1 and 3 both showed attenuation, especially the performance of Example 1 showed a significant attenuation, while the performance of Example 2 showed good stability. This shows that the addition of an appropriate amount of Co2O3 can effectively improve the aging resistance of ceramic materials.

[0072] The piezoelectric ceramic materials prepared in Examples 1-3 were subjected to performance tests, and the results are shown in Table 1.

[0073] Table 1 Properties of piezoelectric ceramic materials prepared in Examples 1-3

[0074]

[0075] It can be seen that the piezoelectric coefficient d of the piezoelectric ceramic prepared by the method of the present invention is 33 72~75pC / N, mechanical quality factor Q m The electromechanical coupling coefficient k is 482~730. p is 18% to 19%, and the dielectric constant ε r The dielectric loss tanδ is 1.43% to 2.74%, and the composite has excellent aging resistance at 150°C.

[0076] Therefore, the use of the piezoelectric ceramics with high mechanical quality factor and high temperature aging resistance and the preparation method described in the present invention can solve the problem that the existing sodium bismuth titanate-based piezoelectric ceramics are severely aged at high temperatures, which affects the stability of the piezoelectric ceramics; and can obtain sodium bismuth titanate-based piezoelectric ceramics with high mechanical quality factor.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A piezoelectric ceramic with high mechanical quality factor and high temperature aging resistance, characterized by: The chemical formula of the piezoelectric ceramic is (Bi 0.5 Na 0.44 K 0.04 Li 0.02 )(Ti 0.977 Co 0.023 )O3.

2. A method for preparing a piezoelectric ceramic with high mechanical quality factor and high temperature aging resistance as claimed in claim 1, characterized in that: The following steps are involved: S1. Weigh analytically pure sodium carbonate Na2CO3, potassium carbonate K2CO3, lithium carbonate LiCO3, bismuth trioxide Bi2O3, titanium dioxide TiO2, and cobalt trioxide Co2O3 according to molar percentage as raw materials, and ball-mill the raw materials to obtain a primary powder; S2, drying the primary powder to obtain a uniformly mixed primary powder; S3, pre-calcining the primary powder to obtain dry powder; S4, performing secondary ball milling on the dry powder to obtain secondary powder; S5, drying the secondary powder to obtain a uniformly mixed secondary powder; S6. Adding a polyvinyl alcohol aqueous solution to the secondary powder and sequentially performing granulation, sieving, pressing and debinding to obtain a ceramic body; S7, sintering the ceramic body to obtain a piezoelectric ceramic body; S8. Silver electrodes are placed on the piezoelectric ceramic body and voltage is applied for polarization.

3. The method for preparing a piezoelectric ceramic with high mechanical quality factor and high temperature aging resistance according to claim 2, characterized in that: In S1, the primary ball milling medium is anhydrous ethanol, the primary ball milling is a planetary ball mill, the ball milling jar is a nylon jar, the grinding balls are zirconium balls, and the primary ball milling time is 6 hours to 10 hours.

4. The method for preparing a piezoelectric ceramic with high mechanical quality factor and high temperature aging resistance according to claim 2, characterized in that: In S3, the powder is pre-fired in a corundum crucible at a temperature of 800° C. to 900° C. for a time of 5 to 8 hours.

5. The method for preparing a piezoelectric ceramic with high mechanical quality factor and high temperature aging resistance according to claim 2, characterized in that: In S4, the ball milling medium for the secondary ball milling is anhydrous ethanol, and the ball milling time for the secondary ball milling is 6 hours to 10 hours.

6. The method for preparing a piezoelectric ceramic with high mechanical quality factor and high temperature aging resistance according to claim 2, characterized in that: In S6, a polyvinyl alcohol aqueous solution with a mass percentage of 6 wt% to 8 wt% is added to the secondary powder, and the screen is sieved with a 120-mesh sieve; the secondary powder is pressed into round tablets using a manual tablet press at a pressure of 8 MPa.

7. The method for preparing a piezoelectric ceramic with high mechanical quality factor and high temperature aging resistance according to claim 2, characterized in that: In the above-mentioned S7, the sintering temperature is 1100° C. to 1150° C., and the sintering time is 1 hour to 3 hours.

8. The method for preparing a piezoelectric ceramic with high mechanical quality factor and high temperature aging resistance according to claim 2, characterized in that: In the above-mentioned S8, the polarization voltage of the piezoelectric ceramic body is 4 kV / cm to 5 kV / cm, and the polarization time is 20 minutes to 40 minutes.

9. The method for preparing a piezoelectric ceramic with high mechanical quality factor and high temperature aging resistance according to any one of claims 2 to 8, characterized in that: The piezoelectric coefficient d of the prepared piezoelectric ceramics 33 72pC / N~75pC / N, mechanical quality factor Q m The electromechanical coupling coefficient k is 482~730. p is 18% to 19%, and the dielectric constant ε r The dielectric loss tanδ is 362~469, the dielectric loss tanδ is 1.43%~2.74%, and it has good aging resistance at a high temperature of 150℃.

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