Lead-free piezoelectric ceramic and its preparation method and application

Abstract

The present invention belongs to the technical field of ceramic material preparation methods, and specifically relates to a lead-free piezoelectric ceramic, its preparation method, and application. The lead-free piezoelectric ceramic is a KNN-based lead-free piezoelectric ceramic or a BT-based lead-free piezoelectric ceramic having a perovskite structure; the KNN-based lead-free piezoelectric ceramic is prepared by doping gallium nitride with potassium sodium niobate (KNN) ceramic as the matrix, and the chemical formula is 0.955 (K 0.48 Na 0.52 )Nb 0.98 Sb 0.02 O3‒0.045Bi 0.5 Na 0.5 ZrO3‒0.75mol% GaN; The BT-based lead-free piezoelectric ceramic is prepared by doping gallium nitride with barium nitride (BT) as the matrix, and the chemical formula is (Ba 0.85 Ca 0.15 )(Ti 0.9 Zr 0.1 ) O‒1.75mol% GaN; the lead-free piezoelectric ceramic has a dense structure, is lead-free, and exhibits excellent electrochemical properties. The preparation method for the lead-free piezoelectric ceramic is simple, low-cost, pollution-free, and utilizes readily available raw materials. The lead-free piezoelectric ceramic can be used to prepare energy harvesters and has significant application value.

Description

Technical Field

[0001] The present invention belongs to the technical field of ceramic material preparation methods, and in particular relates to a lead-free piezoelectric ceramic and a preparation method and application thereof. Background Art

[0002] In recent years, technological advancements have led to rapid development of the Internet of Things (IoT) and the miniaturization of electronic components. These devices have also become smaller, but the batteries that power them are not only short-lived, highly polluting, and relatively large. Consequently, there is an urgent need to find a compact, clean, and long-lasting energy source to replace traditional batteries. Among the many new energy sources, vibration energy harvesters not only convert waste mechanical energy from the environment into electrical energy to continuously power small, low-power electronic devices, but also have a simple structure, good flexibility, and a long service life, making them highly favored by researchers.

[0003] To improve energy harvesting efficiency, it's necessary not only to optimize the overall structure of the energy harvesting device but also to develop materials with high electromechanical conversion coefficients. In recent years, lead-based perovskite ceramics, exemplified by PZT (lead zirconate titanate), have long dominated the energy harvesting device market due to their superior performance. However, their primary component, lead oxide (PbO), is a volatile and toxic substance. Therefore, its production, use, and disposal can easily pollute the environment, posing a serious health risk to humans and other organisms. Therefore, developing a lead-free material with a high electromechanical conversion coefficient is crucial. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the first object of the present invention is to provide a lead-free piezoelectric ceramic; the lead-free piezoelectric ceramic; the lead-free piezoelectric ceramic is composed of a first-phase original ceramic matrix and gallium nitride (GaN) material, has the characteristics of dense structure, is lead-free and has good electrochemical properties.

[0005] The second object of the present invention is to provide a method for preparing the above-mentioned lead-free piezoelectric ceramic; the preparation method has the advantages of simple operation, low cost, no pollution and readily available raw materials.

[0006] The third object of the present invention is to provide an application of the lead-free piezoelectric ceramic; the lead-free piezoelectric ceramic can be used to prepare an energy harvester.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A lead-free piezoelectric ceramic, wherein the lead-free piezoelectric ceramic is a KNN-based lead-free piezoelectric ceramic or a BT-based lead-free piezoelectric ceramic;

[0009] The KNN-based lead-free piezoelectric ceramic is prepared by doping gallium nitride (GaN) with potassium sodium niobate (KNN) ceramic as the matrix; the chemical formula of the KNN-based lead-free piezoelectric ceramic is 0.955 (K 0.48 Na 0.52 )Nb 0.98 Sb 0.02 O3‒0.045Bi 0.5 Na 0.5 ZrO3‒0.75mol% GaN;

[0010] The BT-based lead-free piezoelectric ceramic is prepared by doping gallium nitride (GaN) with barium nitride (BT) as the matrix; the chemical formula of the BT-based lead-free piezoelectric ceramic is (Ba 0.85 Ca 0.15 )(Ti 0.9 Zr 0.1 )O3‒1.75mol% GaN.

[0011] The preparation method of the lead-free piezoelectric ceramic comprises the following steps:

[0012] (1) Weigh the raw materials and mix them;

[0013] (2) Drying the mixed raw materials obtained in step (1), ball milling, and pre-calcining to obtain a powder;

[0014] (3) According to the stoichiometric relationship of each element in the chemical formula in step (1), gallium nitride is added to the powder obtained in step (2), and secondary ball milling is performed to obtain a mixed powder;

[0015] (4) Adding a binder to the mixed powder obtained in step (3) and grinding and granulating the mixture to prepare a round green body;

[0016] (5) Debinding the circular green body obtained in step (4), sintering it, and silver polarizing it to obtain the lead-free piezoelectric ceramic;

[0017] When the lead-free piezoelectric ceramic is a KNN-based lead-free piezoelectric ceramic, in step (1), according to the chemical formula 0.955 (K 0.48 Na 0.52 )Nb 0.98 Sb 0.02 O3‒0.045Bi 0.5 Na 0.5 Stoichiometric relationship of ZrO3‒0.75mol% GaN Weigh K2CO3, Na2CO3, Nb2O5, Bi2O3, Sb2O3 and ZrO2 and mix;

[0018] When the lead-free piezoelectric ceramic is a BT-based lead-free piezoelectric ceramic, in step (1), according to the chemical formula (Ba0.85 Ca 0.15 )(Ti 0.9 Zr 0.1 ) Stoichiometric relationship of O3‒1.75mol% GaN: Weigh BaCO3, CaCO3, TiO2 and ZrO2 and mix them.

[0019] Furthermore, in step (2), the drying temperature is 70-100°C and the drying time is 8-24 h.

[0020] Furthermore, in step (2), the primary ball milling comprises the following steps: adding zirconium oxide balls and anhydrous ethanol to the mixed raw material obtained in step (1) and performing a primary ball milling; the time for the primary ball milling is 8 to 24 hours; and the mass ratio of the mixed raw material, zirconium oxide balls and anhydrous ethanol is 1:15:5.

[0021] Furthermore, the ball milling is further subjected to drying; the drying temperature is 70°C.

[0022] Furthermore, in step (2), the pre-firing temperature is 850-1300° C., and the pre-firing time is 3-6 h.

[0023] Furthermore, in step (3), the secondary ball milling time is 8 to 24 hours.

[0024] Furthermore, in step (4), the pressurizing method for making the circular green body is unidirectional pressurizing; the pressure of the unidirectional pressurizing is 2 MPa; the diameter of the circular green body is 10 mm and the thickness is 1 mm.

[0025] Furthermore, in step (5), the temperature of the debinding treatment is 500-900°C, and the time is 3-6 hours; the temperature of the sintering is 1000-1500°C, and the time is 3-5 hours; the heating rates of the debinding treatment and sintering are both 1-5°C / min.

[0026] Furthermore, in step (5), the silver polarization includes the following steps: brushing silver paste on both sides of the ceramic sample obtained after sintering, baking at 600°C for 30 minutes, placing it in silicone oil, and polarizing it under an electric field of 1~5kV / mm for 15~60 minutes.

[0027] Application of the lead-free piezoelectric ceramics: The lead-free piezoelectric ceramics can be used to prepare energy harvesters.

[0028] The lead-free piezoelectric ceramic provided by the present invention is prepared by doping gallium nitride with KNN ceramic or BT ceramic as a matrix. The gallium nitride is dispersed at the grain boundaries of the ceramic matrix. Due to different expansion coefficients, the grains are squeezed during the sintering process, thereby suppressing the growth of the grains to achieve a uniform microstructure of the ceramic. At the same time, the dielectric constant of the ceramic is reduced, thereby improving the energy conversion coefficient of the ceramic. Moreover, by controlling the sintering conditions, the gallium nitride itself does not undergo phase change. After the gallium nitride is doped, the performance of the ceramic is significantly improved compared with the original ceramic.

[0029] Beneficial effects

[0030] (1) The lead-free piezoelectric ceramic provided by the present invention is prepared by doping gallium nitride with KNN ceramic or BT ceramic as a matrix, that is, the lead-free piezoelectric ceramic is a KNN-based lead-free piezoelectric ceramic or a BT-based lead-free piezoelectric ceramic; the lead-free piezoelectric ceramic has good crystallinity and presents a typical perovskite structure, with dense grains and good dielectric properties; the lead-free piezoelectric ceramic can be used to prepare energy collectors.

[0031] The piezoelectric voltage constant of the KNN-based lead-free piezoelectric ceramic is 14.92 (10 -3 Vm / N), the electromechanical conversion factor is 5318 (10 -15 m 2 / N). The energy harvester made of KNN-based lead-free piezoelectric ceramics can achieve an open circuit voltage of 10.5V, a short circuit current of 17.98µA, and a maximum power density of 46.9µW under 1G acceleration vibration excitation. The piezoelectric voltage constant of the BT-based lead-free piezoelectric ceramics is 15.3 (10 -3 Vm / N), the electromechanical conversion factor is 10022 (10 -15 m 2 / N). An energy harvester fabricated from BT-based lead-free piezoelectric ceramics, tested under 1G acceleration vibration excitation, achieved an open-circuit voltage of 20.5V, a short-circuit current of 21.1µA, and a maximum power density of 99.5µW. The incorporation of gallium nitride into the ceramic significantly improves the electromechanical conversion coefficient, thereby achieving higher energy harvesting efficiency.

[0032] (2) The preparation method of the lead-free piezoelectric ceramic provided by the present invention has the advantages of simple operation, low cost, no pollution and easy availability of raw materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The XRD pattern of the KNN-based lead-free piezoelectric ceramic prepared in Example 1;

[0034] Figure 2 This is a SEM image of the KNN-based lead-free piezoelectric ceramic prepared in Example 1;

[0035] Figure 3 The dielectric-temperature spectrum of the KNN-based lead-free piezoelectric ceramic prepared in Example 1;

[0036] Figure 4 This is a hysteresis loop diagram of the KNN-based lead-free piezoelectric ceramic prepared in Example 1;

[0037] Figure 5 1 is a strain curve diagram of the KNN-based lead-free piezoelectric ceramic prepared in Example 1;

[0038] Figure 6 This is an open circuit voltage curve of the energy harvester prepared in Example 1;

[0039] Figure 7 This is a short-circuit current curve of the energy harvester prepared in Example 1;

[0040] Figure 8 This is a graph showing the average output voltage, current, and power density of the energy harvester prepared in Example 1; Figure 8 a is the average output voltage diagram; Figure 8 b is the current diagram; Figure 8 c is the power density curve;

[0041] Figure 9 The XRD pattern of the BT-based lead-free piezoelectric ceramic prepared in Example 2;

[0042] Figure 10 This is a SEM image of the BT-based lead-free piezoelectric ceramic prepared in Example 2;

[0043] Figure 11 The dielectric-temperature spectrum of the BT-based lead-free piezoelectric ceramic prepared in Example 2;

[0044] Figure 12 This is the hysteresis loop diagram of the BT-based lead-free piezoelectric ceramic prepared in Example 2;

[0045] Figure 13 This is a strain curve diagram of the BT-based lead-free piezoelectric ceramic prepared in Example 2;

[0046] Figure 14 This is an open circuit voltage curve of the energy harvester prepared in Example 2;

[0047] Figure 15 This is a short-circuit current curve of the energy harvester prepared in Example 2;

[0048] Figure 16 This is a graph showing the average output voltage, current, and power density of the energy harvester prepared in Example 2; Figure 16 a is the average output voltage diagram; Figure 16 b is the current diagram; Figure 16 c is the power density curve;

[0049] Figure 17 The XRD pattern of the ceramic material prepared in Comparative Example 1;

[0050] Figure 18 This is an SEM image of the ceramic material prepared in Comparative Example 1;

[0051] Figure 19 The dielectric temperature spectrum of the ceramic material prepared in Comparative Example 1;

[0052] Figure 20 This is a hysteresis loop diagram of the ceramic material prepared in Comparative Example 1;

[0053] Figure 21 This is a strain curve diagram of the ceramic material prepared in Comparative Example 1;

[0054] Figure 22 This is an open circuit voltage curve of the energy harvester prepared in Comparative Example 1;

[0055] Figure 23 This is a short-circuit current curve of the energy harvester prepared in Comparative Example 1;

[0056] Figure 24 The average output voltage, current and power density curves of the energy harvester prepared in Comparative Example 1; Figure 24 a is the average output voltage diagram; Figure 24 b is the current diagram; Figure 24 c is the power density curve;

[0057] Figure 25 This is the synchrotron radiation XRD pattern of the ceramic material prepared in Comparative Example 2;

[0058] Figure 26 This is an SEM image of the ceramic material prepared in Comparative Example 2;

[0059] Figure 27 This is the dielectric temperature spectrum of the ceramic material prepared in Comparative Example 2;

[0060] Figure 28 This is a hysteresis loop diagram of the ceramic material prepared in Comparative Example 2;

[0061] Figure 29 This is a strain curve diagram of the ceramic material prepared in Comparative Example 2;

[0062] Figure 30 This is an open circuit voltage curve of the energy harvester prepared in Comparative Example 2;

[0063] Figure 31 This is a short-circuit current curve of the energy harvester prepared in Comparative Example 2;

[0064] Figure 32 This is a graph showing the average output voltage, current, and power density of the energy harvester prepared in Comparative Example 2; Figure 32 a is the average output voltage diagram; Figure 32 b is the current diagram; Figure 32 c is the power density curve. DETAILED DESCRIPTION

[0065] In order to further describe the present invention in detail, the following specific implementation examples are given, but they are only used to illustrate the present invention and make the steps clearer, and are not intended to limit the scope of application of the present invention.

[0066] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods. Unless otherwise specified, the materials, reagents, etc. used in the following examples are all commercially available.

[0067] The dielectric properties of the ceramics prepared in the following Examples 1-2 and Comparative Examples 1-2 were tested according to the methods disclosed in the National Standards of the People's Republic of China, "Quasi-static Test Method for Hysteresis Loops of Ferroelectric Ceramic Materials" (GB / T6426-1999); "Test Method for Dielectric Properties of Dielectric Crystals" (GB / T 16822-1997); "Piezoelectric Ceramic Material Performance Test Method - Test of Electric Field Strain Characteristics" (GB / T 16304-2008); "Piezoelectric Ceramic Material Performance Test Method - Column Longitudinal Length Extension Vibration Mode" (GB / T3389.5-1995); and "Piezoelectric Ceramic Material Performance Test Method - Test of Performance Parameters" (GB / T 3389-2008).

[0068] Example 1

[0069] KNN-based composite 0.75mol% GaN ceramics (KNN-based lead-free piezoelectric ceramics), the chemical formula of which is 0.955(K 0.48 Na 0.52 )Nb 0.98 Sb 0.02 O3‒0.045Bi 0.5 Na 0.5 ZrO3‒0.75mol% GaN.

[0070] The specific preparation method comprises the following steps:

[0071] (1) According to the above chemical formula, K2CO3, Na2CO3, Nb2O5, Bi2O3, Sb2O3, and ZrO2 were weighed and dried in a vacuum drying oven at 90 °C for 12 h. The raw materials, zirconium oxide balls, and anhydrous ethanol (mass ratio of 1:15:15) were then placed in a nylon jar and ball milled in a planetary ball mill for 24 h.

[0072] (2) The ball-milled slurry was dried at 70 °C and then pre-calcined in a muffle furnace at 850 °C for 6 h;

[0073] (3) GaN was weighed according to the stoichiometric ratio, added to the pre-sintered powder, and ball milled again for 24 hours;

[0074] (4) After ball milling for 24 hours and drying, an appropriate amount of polyvinyl butyral binder was added for grinding and granulation, and uniaxial pressure molding was performed at 2 MPa to obtain a ceramic circular green body with a diameter of about 10 mm and a thickness of about 1 mm;

[0075] (5) The disc obtained in step (4) was heated to 600 °C at a rate of 3 °C / min and kept at this temperature for 3 h for debinding. The disc after debinding was sintered at 1140-1170 °C for 3 h to prepare piezoelectric ceramic samples. The crystal structure and microstructure of the sintered ceramics were analyzed. The results are as follows: Figure 1 and Figure 2 As shown;

[0076] (6) The sintered ceramic was printed with high-temperature silver paste on both sides, baked at 600 °C for 0.5 h, allowed to stand for 24 h, and then placed in silicone oil and polarized at an electric field of 3 kV / mm for 15 min to obtain the KNN-based lead-free piezoelectric ceramic. The electrical properties of the ceramic sample containing silver electrodes were tested.

[0077] (7) Preparation of ceramics as cantilever energy harvesters. The structure is to connect a vibration screen of model HEV-20 produced by Nanjing Fo Neng Company to a custom fixture. A Shanghai Chengke CT1050LC accelerometer is loaded on top of the custom fixture. Then a cantilever beam with a size of 120 mm × 12 mm × 0.9 mm is clamped to the fixture. A square piezoelectric ceramic piece is loaded on the cantilever beam at a suitable stress point. Finally, it is connected to a Keysight InfiniiVision DSOX3014T oscilloscope and a 2450 digital source meter from the United States. The HEAS-20 power amplifier produced by Nanjing Fo Neng Company is responsible for giving the system an alternating signal. Finally, the voltage and current can be measured at the test end to characterize the energy harvesting capability of the piezoelectric ceramic.

[0078] Figure 1 This is the X-ray diffraction (XRD) pattern of the KNN-based lead-free piezoelectric ceramic prepared in this embodiment. It can be seen from the figure that the prepared KNN-based ceramic has good crystallinity and presents a typical perovskite structure.

[0079] Figure 2 This is a scanning electron microscope (SEM) image of the KNN-based lead-free piezoelectric ceramic. It can be seen from the image that the ceramic grains are sintered densely without obvious pores.

[0080] Conduct dielectric property tests on ceramics. Figure 3 The dielectric temperature spectrum of KNN-based lead-free piezoelectric ceramics. Figure 3 It can be seen from the dielectric temperature curve that in the range of -120~400 °C, the prepared two-phase lead-free perovskite ceramics presents the coexistence of R‒O‒T three phases, and the dielectric loss is also very small at room temperature, which is 0.028.

[0081] Figure 4 This is the hysteresis loop spectrum of KNN-based lead-free piezoelectric ceramics. It can be seen that a saturated hysteresis loop is displayed under an electric field, indicating that the ceramics have good ferroelectric properties.

[0082] Figure 5 This is the strain curve of KNN-based lead-free piezoelectric ceramics under electric field. The strain can reach 0.16%. .

[0083] Figure 6 The open circuit voltage curve of the prepared ceramic energy harvester tested under 1G acceleration vibration excitation can reach 10.5V.

[0084] Figure 7 The short-circuit current curve of the prepared ceramic energy harvester tested under 1G acceleration vibration excitation can reach 17.98µA.

[0085] Figure 8 The average output voltage of the prepared ceramic energy harvester tested under 1G acceleration and different load resistances ( Figure 8 a) Current ( Figure 8 b) and power density ( Figure 8 c) Graph showing that as the load resistance increases, the output current decreases and the output voltage increases, with the maximum power density reaching 46.9µW.

[0086] The piezoelectric voltage constant of KNN-based lead-free piezoelectric ceramics is calculated according to the formula g 33 = d 33 / ε 0 ε r The result is 14.92 (10 -3 Vm / N), the conversion coefficient is based on the formula d 33 × g 33 The result is 5318 (10 -15 m 2 / N).

[0087] Example 2

[0088] BT-based composite 1.75mol% GaN ceramics (BT-based lead-free piezoelectric ceramics), the chemical formula is (Ba 0.85 Ca 0.15 )(Ti 0.9 Zr 0.1 )O3‒1.75mol% GaN.

[0089] The specific preparation method comprises the following steps:

[0090] (1) BaCO3, CaCO3, TiO2, and ZrO2 were weighed according to the above chemical formula and dried in a vacuum drying oven at 90 °C for 12 h. The raw materials, zirconium oxide balls, and anhydrous ethanol (mass ratio of 1:15:15) were then placed in a nylon jar and ball milled in a planetary ball mill for 24 h.

[0091] (2) The ball-milled slurry was dried at 70 °C and then pre-calcined in a muffle furnace at 1300 °C for 3 h;

[0092] (3) GaN was weighed according to the stoichiometric ratio, added to the pre-sintered powder, and ball milled again for 24 hours;

[0093] (4) After ball milling for 24 hours and drying, an appropriate amount of polyvinyl butyral binder was added for grinding and granulation, and uniaxial pressure molding was performed at 2 MPa to obtain a ceramic circular green body with a diameter of about 10 mm and a thickness of about 1 mm;

[0094] (5) The disc obtained in step (4) was heated to 600 °C at a rate of 3 °C / min and kept at this temperature for 3 h for debinding. The disc after debinding was sintered at 1420-1460 °C for 3 h to prepare piezoelectric ceramic samples. The crystal structure and microstructure of the sintered ceramics were analyzed. The results are as follows: Figure 9 and Figure 10 As shown;

[0095] (6) Print high-temperature silver paste on both sides of the sintered ceramic, bake at 600 °C for 0.5 h, and then test the electrical properties of the ceramic sample containing silver electrodes after standing for 24 h;

[0096] The sintered ceramic was printed with high-temperature silver paste on both sides, baked at 600 °C for 0.5 h, allowed to stand for 24 h, and then placed in silicone oil and polarized at an electric field of 3 kV / mm for 15 min to test the dielectric properties of the ceramic sample containing silver electrodes.

[0097] (7) Preparation of ceramics as cantilever energy harvesters. The structure is to connect a vibration screen of model HEV-20 produced by Nanjing Fo Neng Company to a custom fixture. A Shanghai Chengke CT1050LC accelerometer is loaded on top of the custom fixture. Then a cantilever beam with a size of 120 mm × 12 mm × 0.9 mm is clamped to the fixture. A square piezoelectric ceramic piece is loaded on the cantilever beam at a suitable stress point. Finally, it is connected to a Keysight InfiniiVision DSOX3014T oscilloscope and a 2450 digital source meter from the United States. The HEAS-20 power amplifier produced by Nanjing Fo Neng Company is responsible for giving the system an alternating signal. Finally, the voltage and current can be measured at the test end to characterize the energy harvesting capability of the piezoelectric ceramic.

[0098] Figure 9 This is the XRD pattern of the BT-based lead-free piezoelectric ceramic prepared in this example. It can be seen from the figure that the BT-based lead-free piezoelectric ceramic has good crystallinity and presents a typical perovskite structure.

[0099] Figure 10 This is the SEM image of BT-based lead-free piezoelectric ceramics. It can be seen from the figure that the ceramic grains are sintered densely and there are no obvious pores.

[0100] Conduct electrical performance tests on ceramics. Figure 11 This is the dielectric-temperature spectrum of BT-based lead-free piezoelectric ceramics tested in the temperature range of -50~200 °C. The results show that in the range of -50–200 °C, the three phases R‒O‒T coexist, and the dielectric loss is also very small at room temperature.

[0101] Figure 12 This is the hysteresis loop spectrum of BT-based lead-free piezoelectric ceramics tested at 1 Hz and room temperature. The results show that BT-based lead-free piezoelectric ceramics exhibit a saturated hysteresis loop under an electric field.

[0102] Figure 13 The strain curve of BT-based lead-free piezoelectric ceramics tested at 1 Hz and room temperature shows that the strain of BT-based lead-free piezoelectric ceramics under electric field can reach 0.19%. .

[0103] Figure 14 The open circuit voltage curve of the prepared energy harvester was obtained by testing under 1G acceleration vibration excitation. The results show that the open circuit voltage can reach 20.5V.

[0104] Figure 15 The short-circuit current curve of the prepared energy harvester was obtained by testing under 1G acceleration vibration excitation. The results show that the short-circuit current can reach 21.1µA.

[0105] Figure 16The average output voltage of the prepared energy harvester tested under 1G acceleration and different load resistances ( Figure 16 a) Current ( Figure 16 b) and power density ( Figure 16 c) Curve. The results show that as the load resistance increases, the output current decreases and the output voltage increases, and the maximum power density can reach 99.5µW.

[0106] In addition, the piezoelectric voltage constant of the ceramic is given by the formula g 33 = d 33 / ε 0 ε r The result is 15.3 (10 -3 Vm / N), the conversion coefficient is based on the formula d 33 × g 33 The result is 10022 (10 -15 m 2 / N).

[0107] Comparative Example 1

[0108] KNN-based ceramics without gallium nitride (GaN) doping, with a chemical formula of 0.955 (K 0.48 Na 0.52 )Nb 0.98 Sb 0.02 O3‒0.045Bi 0.5 Na 0.5 ZrO3.

[0109] The specific preparation method comprises the following steps:

[0110] (1) According to the above chemical formula, K2CO3, Na2CO3, Nb2O5, Bi2O3, Sb2O3, and ZrO2 were weighed and dried in a vacuum drying oven at 90 °C for 12 h. The raw materials, zirconium oxide balls, and anhydrous ethanol (mass ratio of 1:15:15) were then placed in a nylon jar and ball milled in a planetary ball mill for 24 h.

[0111] (2) The ball-milled slurry was dried at 70 °C and then pre-calcined in a muffle furnace at 850 °C for 3 h;

[0112] (3) Place the pre-calcined powder in a nylon jar and ball mill again for 24 hours;

[0113] (4) After ball milling for 24 hours and drying, an appropriate amount of polyvinyl butyral binder was added for grinding and granulation, and uniaxial pressure molding was performed at 2 MPa to obtain a ceramic circular green body with a diameter of about 10 mm and a thickness of about 1 mm;

[0114] (5) The disc obtained in step (4) was heated to 600 °C at a rate of 3 °C / min and kept at this temperature for 3 h for debinding. The disc after debinding was sintered at 1140-1170 °C for 3 h to prepare a piezoelectric ceramic sample. The crystal structure and microstructure of the sintered ceramic were analyzed. The results are as follows: Figure 17 and Figure 18 As shown;

[0115] (6) After sintering, high-temperature silver paste was printed on both sides of the ceramic, baked at 600 °C for 0.5 h, allowed to stand for 24 h, and then placed in silicone oil and polarized at an electric field of 3 kV / mm for 15 min. The dielectric properties of the ceramic sample containing silver electrodes were tested;

[0116] (7) Preparation of ceramics as cantilever energy harvesters. The structure is to connect a vibration screen of model HEV-20 produced by Nanjing Fo Neng Company to a custom fixture. A Shanghai Chengke CT1050LC accelerometer is loaded on top of the custom fixture. Then a cantilever beam with a size of 120 mm × 12 mm × 0.9 mm is clamped to the fixture. A square piezoelectric ceramic piece is loaded on the cantilever beam at a suitable stress point. Finally, it is connected to a Keysight InfiniiVision DSOX3014T oscilloscope and a 2450 digital source meter from the United States. The HEAS-20 power amplifier produced by Nanjing Fo Neng Company is responsible for giving the system an alternating signal. Finally, the voltage and current can be measured at the test end to characterize the energy harvesting capability of the piezoelectric ceramic.

[0117] Figure 17 This is the XRD pattern of KNN-based ceramics without GaN doping. It can be seen from the figure that the prepared KNN-based ceramics have good crystallinity and present a typical perovskite structure.

[0118] Figure 18 This is a SEM image of a KNN-based ceramic without GaN doping. As can be seen from the image, the ceramic grains are sintered densely without obvious pores.

[0119] Conduct dielectric property tests on ceramics. Figure 19 The figure shows the dielectric-temperature spectrum of KNN-based ceramics without GaN doping tested in the temperature range of -50~200 °C. It can be seen from the figure that in the range of -120~400 °C, the prepared two-phase lead-free piezoelectric ceramics show the coexistence of R‒O‒T three phases, and the dielectric loss is also very small at room temperature.

[0120] Figure 20 The hysteresis loop of the KNN-based ceramic without GaN doping was obtained by testing at 1 Hz and room temperature. As can be seen from the figure, the KNN-based ceramic without GaN doping shows a saturated hysteresis loop under the electric field, indicating that the ceramic has good ferroelectric properties.

[0121] Figure 21 The strain curve of KNN-based ceramics without GaN doping was obtained at 1 Hz and room temperature. It can be seen from the figure that the strain of KNN-based ceramics without GaN doping can reach 0.11%. .

[0122] Figure 22 This is the open-circuit voltage curve of the energy harvester tested under 1G acceleration vibration excitation. The results show that the open-circuit voltage can reach 5.5V.

[0123] Figure 23 The short-circuit current curve of the energy harvester tested under 1G acceleration vibration excitation shows that the short-circuit current can reach 12.1µA.

[0124] Figure 24 is the average output voltage of the energy harvester tested under 1G acceleration and different load resistances ( Figure 24 a) Current ( Figure 24 b) and power density ( Figure 24 c) Curve. The results show that as the load resistance increases, the output current decreases and the output voltage increases, and the maximum power density can reach 12.3µW.

[0125] In addition, the piezoelectric voltage constant of the ceramic is given by the formula g 33 = d 33 / ε 0 ε r The result is 12.56 (10 -3 Vm / N), the conversion coefficient is based on the formula d 33 × g 33 The result is 3528 (10 -15 m 2 / N).

[0126] Comparative Example 2

[0127] BT-based ceramics without gallium nitride (GaN) doping, the chemical formula of which is (Ba 0.85 Ca 0.15 )(Ti 0.9 Zr 0.1 )O3.

[0128] The specific preparation method comprises the following steps:

[0129] (1) BaCO3, CaCO3, TiO2, and ZrO2 were weighed according to the above chemical formula and dried in a vacuum drying oven at 90 °C for 12 h. The raw materials, zirconium oxide balls, and anhydrous ethanol (mass ratio of 1:15:15) were then placed in a nylon jar and ball milled in a planetary ball mill for 24 h.

[0130] (2) The ball-milled slurry was dried at 70°C and then pre-calcined in a muffle furnace at 1300°C for 3 h.

[0131] (3) Place the pre-calcined powder in a nylon jar and ball mill again for 24 hours;

[0132] (4) After ball milling for 24 hours and drying, an appropriate amount of polyvinyl butyral binder was added for grinding and granulation, and uniaxial pressure molding was performed at 2 MPa to obtain a ceramic circular green body with a diameter of about 10 mm and a thickness of about 1 mm;

[0133] (5) The disc obtained in step (4) was heated to 600 °C at a rate of 3 °C / min and kept at this temperature for 3 h for debinding. The disc after debinding was sintered at 1420-1460 °C for 3 h to prepare a piezoelectric ceramic sample. The crystal structure and microstructure of the sintered ceramic were analyzed. The results are as follows: Figure 25 and Figure 26 As shown;

[0134] (6) After sintering, high-temperature silver paste was printed on both sides of the ceramic, baked at 600 °C for 0.5 h, allowed to stand for 24 h, and then placed in silicone oil and polarized at an electric field of 3 kV / mm for 15 min. The dielectric properties of the ceramic sample containing silver electrodes were tested;

[0135] (7) Preparation of ceramics as cantilever energy harvesters. The structure is to connect a vibration screen of model HEV-20 produced by Nanjing Fo Neng Company to a custom fixture. A Shanghai Chengke CT1050LC accelerometer is loaded on top of the custom fixture. Then a cantilever beam with a size of 120 mm × 12 mm × 0.9 mm is clamped to the fixture. A square piezoelectric ceramic piece is loaded on the cantilever beam at a suitable stress point. Finally, it is connected to a Keysight InfiniiVision DSOX3014T oscilloscope and a 2450 digital source meter from the United States. The HEAS-20 power amplifier produced by Nanjing Fo Neng Company is responsible for giving the system an alternating signal. Finally, the voltage and current can be measured at the test end to characterize the energy harvesting capability of the piezoelectric ceramic.

[0136] Figure 25 This is the XRD pattern of BT-based ceramics without GaN doping. It can be seen from the figure that BT-based ceramics have good crystallinity and present a typical perovskite structure.

[0137] Figure 26This is the SEM image of BT-based ceramics without GaN doping. It can be seen from the figure that the ceramic grains are sintered densely without obvious pores.

[0138] Conduct dielectric property tests on ceramics. Figure 27 The figure shows the dielectric-temperature spectrum of BT-based ceramics without GaN doping tested in the temperature range of -50~200 °C. It can be seen that in the range of -50~200 °C, the prepared two-phase lead-free piezoelectric ceramics presents the coexistence of R‒O‒T three phases, and the dielectric loss is also very small at room temperature.

[0139] Figure 28 The hysteresis loop of BT-based ceramics without GaN doping was obtained by testing at 1 Hz and room temperature. As can be seen from the figure, BT-based ceramics without GaN doping show a saturated hysteresis loop under an electric field, indicating that the ceramics have good ferroelectric properties.

[0140] Figure 29 The strain curve of BT-based ceramics without GaN doping was obtained by testing at 1 Hz and room temperature. It can be seen from the figure that the strain of BT-based ceramics without GaN doping can reach 0.13%. .

[0141] Figure 30 This is the open circuit voltage curve of the energy harvester prepared in comparative example 2 tested under 1G acceleration vibration excitation. As can be seen from the figure, the open circuit voltage can reach 13.2V.

[0142] Figure 31 The short-circuit current curve of the energy harvester prepared in comparative example 2 was obtained by testing under 1G acceleration vibration excitation. As can be seen from the figure, the short-circuit current can reach 16.1µA.

[0143] Figure 32 is the average output voltage of the energy harvester tested under 1G acceleration and different load resistances ( Figure 32 a) Current ( Figure 32 b) and power density ( Figure 32 c) Curve. The results show that as the load resistance increases, the output current decreases and the output voltage increases. As can be seen from the figure, the maximum power density can reach 73.9µW.

[0144] In addition, the piezoelectric voltage constant of the ceramic is given by the formula g 33 = d 33 / ε 0 ε r The result is 13.47 (10 -3 Vm / N), the conversion coefficient is based on the formula d33 × g 33 The result is 7945 (10 -15 m 2 / N).

Claims

1. A lead-free piezoelectric ceramic, characterized in that: The lead-free piezoelectric ceramic is a KNN-based lead-free piezoelectric ceramic or a BT-based lead-free piezoelectric ceramic; the structure of the lead-free piezoelectric ceramic is a perovskite structure; The KNN-based lead-free piezoelectric ceramic is prepared by doping gallium nitride with KNN ceramic as the matrix; the chemical formula of the KNN-based lead-free piezoelectric ceramic is 0.955 (K 0.48 Na 0.52 )Nb 0.98 Sb 0.02 O3‒0.045Bi 0.5 Na 0.5 ZrO3‒0.75mol% GaN; The BT-based lead-free piezoelectric ceramic is prepared by doping gallium nitride with BT ceramic as the matrix; the chemical formula of the BT-based lead-free piezoelectric ceramic is (Ba 0.85 Ca 0.15 )(Ti 0.9 Zr 0.1 )O3‒1.75mol% GaN.

2. The method for preparing the lead-free piezoelectric ceramic according to claim 1, wherein: The preparation method comprises the following steps: (1) Weigh the raw materials and mix them; (2) Drying the mixed raw materials obtained in step (1), ball milling once, and pre-calcining to obtain a powder; (3) According to the stoichiometric relationship of each element in the chemical formula in step (1), gallium nitride is added to the powder obtained in step (2), and secondary ball milling is performed to obtain a mixed powder; (4) Adding a binder to the mixed powder obtained in step (3) and grinding and granulating the mixture to prepare a round green body; (5) Debinding the circular green body obtained in step (4), sintering it, and silver polarizing it to obtain the lead-free piezoelectric ceramic; When the lead-free piezoelectric ceramic is a KNN-based lead-free piezoelectric ceramic, in step (1), according to the chemical formula 0.955 (K 0.48 Na 0.52 )Nb 0.98 Sb 0.02 O3‒0.045Bi 0.5 Na 0.5 Stoichiometric relationship of ZrO3‒0.75mol% GaN Weigh K2CO3, Na2CO3, Nb2O5, Bi2O3, Sb2O3 and ZrO2 and mix; When the lead-free piezoelectric ceramic is a BT-based lead-free piezoelectric ceramic, in step (1), according to the chemical formula (Ba 0.85 Ca 0.15 )(Ti 0.9 Zr 0.1 ) Stoichiometric relationship of O3‒1.75mol% GaN: Weigh BaCO3, CaCO3, TiO2 and ZrO2 and mix them.

3. The preparation method according to claim 2, wherein In step (2), the drying temperature is 70-100°C and the drying time is 8-24 hours; The first ball milling is to add zirconium oxide balls and anhydrous ethanol to the mixed raw materials obtained in step (1) and perform a first ball milling; the time of the first ball milling is 8 to 24 hours; The mass ratio of the mixed raw material, zirconium oxide balls and anhydrous ethanol is 1:15:5; After the first ball milling, the product needs to be dried; the drying temperature is 70°C.

4. The preparation method according to claim 2, wherein In step (2), the pre-firing temperature is 850-1300°C and the pre-firing time is 3-6 h.

5. The preparation method according to claim 2, wherein In step (3), the secondary ball milling time is 8 to 24 hours.

6. The preparation method according to claim 2, wherein In step (4), the pressurizing method for preparing the circular green body is unidirectional pressurizing; the pressure of the unidirectional pressurizing is 2 MPa; the diameter of the circular green body is 10 mm and the thickness is 1 mm.

7. The preparation method according to claim 2, wherein In step (5), the temperature of the debinding treatment is 500~900°C, and the time is 3~6 h; the temperature of the sintering is 1000~1500°C, and the time is 3~5 h; the heating rates of the debinding treatment and sintering are both 1~5°C / min.

8. The preparation method according to claim 2, wherein In step (5), the silver polarization includes the following steps: brushing silver paste on both sides of the ceramic sample obtained after sintering, baking at 600°C for 30 minutes, placing it in silicone oil, and polarizing it under an electric field of 1~5 kV / mm for 15~60 minutes.

9. Use of the lead-free piezoelectric ceramic according to claim 1 or the lead-free piezoelectric ceramic prepared by the method according to any one of claims 2 to 8, characterized in that: The lead-free piezoelectric ceramic is used for preparing an energy collector.

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