A high-energy storage sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic and its preparation method and application

Abstract

The present invention belongs to the technical field of ceramics, and discloses a sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic with high energy storage, its preparation method and application. The chemical formula of the ferroelectric ceramic is (1-x)(0.7Na 0.5 Bi 0.5 TiO3 - 0.3Sr 0.7 Bi 0.2 TiO3) - xBi(Mg 0.5 Zr 0.5 )O3, where 0 < x ≤ 0.18. This ceramic has good temperature stability, frequency stability, a large saturation polarization intensity, a low remanent polarization intensity, and a higher breakdown field strength. The energy storage density of the ferroelectric ceramic of the present invention is 4.7 J / cm 3 or more, and the energy storage efficiency is 75% or more, which is suitable for high-power pulse devices.

Description

Technical Field

[0001] The present invention belongs to the technical field of ceramic materials, and more specifically, relates to a high-energy storage sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic, a preparation method thereof, and an application thereof. Background Art

[0002] With the continuous development of energy storage technology and the increasing demand for energy supply, efficient and clean energy storage capacitors are constantly being developed and reported. Dielectric functional ceramics are suitable for scenarios with high instantaneous power demand due to their advantages such as high power density, extremely short charge and discharge time, long cycle life, safety and stability, and are widely used in military and medical fields. However, the energy storage density of commercial dielectric capacitors that have been mass-produced in life is generally less than 2J / cm 3 , so it is meaningful to develop dielectric capacitors with higher energy storage density and higher energy storage efficiency.

[0003] Generally speaking, the total energy storage density (W tot ), recoverable energy storage density (W rec ) and energy storage efficiency (η) can be calculated using the PE hysteresis loop according to formulas (1)-(3):

[0004]

[0005]

[0006]

[0007] Where P m 、P r and E represent the saturation polarization intensity, residual polarization intensity and external electric field respectively. As shown in the above formula, high dielectric breakdown field strength and large ΔP(P m -P r ) are two key factors in achieving high energy storage performance in dielectric materials. If high energy storage density is required, a high W rec , high η and good working stability.

[0008] Although sodium bismuth titanate ceramics have a high maximum polarization intensity P max , but due to its higher coercive electric field and higher P r This results in extremely low energy storage density and efficiency of the matrix. Therefore, it is necessary to dope and modify sodium bismuth titanate ceramics to achieve higher energy storage density and efficiency at a certain temperature, while also obtaining ceramics with excellent energy storage performance over a wide temperature range, which has important practical significance for applications in the field of electronic devices at conventional temperatures. Summary of the Invention

[0009] In order to address the deficiencies and shortcomings of the above-mentioned prior art, the primary purpose of the present invention is to provide a high-energy storage sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic. The ceramic has good temperature stability, frequency stability, large saturation polarization strength, low residual polarization strength, and higher breakdown electric field strength. Its energy storage density is 4.8 J / cm 3 Above, the energy storage efficiency is more than 75%.

[0010] Another object of the present invention is to provide a method for preparing the aforementioned sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic. This method improves energy storage density and efficiency by regulating the composition of the sodium bismuth titanate ceramic system, while also ensuring good stability over a wide temperature range and frequency range.

[0011] Another object of the present invention is to provide an application of the above-mentioned sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic.

[0012] The purpose of the present invention is achieved through the following technical solutions:

[0013] A high energy storage sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic, the chemical formula of which is (1-x)(0.7Na 0.5 Bi 0.5 TiO3-0.3Sr 0.7 Bi 0.2 TiO3)-xBi(Mg 0.5 Zr 0.5 )O3, where x represents the mole fraction, 0 <x≤0.18。

[0014] Preferably, the energy storage density of the ferroelectric ceramic is 4.7 J / cm 3 Above, the energy storage efficiency is more than 75%.

[0015] Preferably, the chemical formula of the ferroelectric ceramic is (0.85)(0.7Na 0.5 Bi 0.5 TiO3-0.3Sr 0.7 Bi 0.2 TiO3)-0.15Bi(Mg 0.5 Zr 0.5 )O3.

[0016] Preferably, the energy storage density of the ferroelectric ceramic is 6.75 J / cm 3 , the energy storage efficiency is 79.44%.

[0017] The preparation method of the high energy storage sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic comprises the following steps:

[0018] S1. Na2CO3, Bi2O3, TiO2, SrCO3, ZrO2 and MgO are uniformly mixed to obtain a ceramic powder;

[0019] S2. The ceramic powder is calcined at 845-855°C, then naturally cooled in the furnace, and a binder, polyvinyl butyral, is added (which has a higher degree of ceramic adhesion than common binders such as polyurethane and polyvinyl alcohol and leaves no residue during the firing and debinding process) to obtain a powder mass. The powder mass is then axially pressed at a pressure of 5-10 MPa to obtain a green body, which is then cold isostatically pressed at 195-205 MPa to obtain a ceramic body.

[0020] S3. The ceramic body is first heated to 595-605°C and kept warm, then heated to 1130-1195°C for sintering, and then cooled to 1000-1120°C to obtain a sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic with high energy storage.

[0021] Preferably, the calcination time in step S2 is 3 to 4 hours, and the axial pressing time is 3 to 5 minutes.

[0022] Preferably, the insulation time in step S3 is 6 to 7 hours, and the sintering time is 4 to 5 hours.

[0023] The application of the high energy storage sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic in high power pulse devices. The power density of the high energy storage ceramic reaches 48.73MW / cm 3 , i.e. 1cm 3 The power of this ceramic is 48730KW, which is tens of thousands times the energy of one kilowatt-hour (3.6KW).

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The ceramic of the present invention is (1-x)(0.7Na 0.5 Bi 0.5 TiO3-0.3Sr 0.7 Bi 0.2 TiO3)-xBi(Mg 0.5 Zr 0.5 )O3,Bi(Mg 0.5 Zr 0.5 The incorporation of )O3 causes the ceramic to transform from a rhombic phase to a tetragonal phase, while also reducing the grain size, increasing the grain boundary density, and making the ceramic denser, which will help improve the breakdown field strength. The ceramic has good temperature stability, frequency stability, large saturation polarization intensity, low residual polarization intensity, and higher breakdown electric field strength. Its energy storage density is 4.8J / cm 3 Above, the energy storage efficiency is above 75%. 0.5 Zr0.5 The incorporation of )O3 leads to an increase in the tilt of oxygen octahedrons, ultimately enhancing the short-range structural disorder, inducing nano-polar microdomains, and further improving the relaxor properties of the material. The average breakdown field strength increases from 165.92kV / cm in the matrix component (x=0) to 393.39kV / cm in the optimized group (x=0.15). After the optimized group, it decreases with the increase of the incorporation amount. The maximum ΔP (50.58μC / cm) is obtained in the optimized group (x=0.15). 2 ), energy storage density is 6.75J / cm 3 The efficiency is 79.44%. In the variable temperature range (20-180℃), as the temperature increases, the efficiency increases from 75.6% (20℃) to 90.92% (110℃), and the deviation value is reduced to 13.2%. Its temperature stability is excellent; in the frequency range of 1-200Hz, W rec The change is 12.6%, which proves that its frequency stability is good.

[0026] 2. This invention produces environmentally friendly, non-toxic, lead-free ceramics with high energy storage performance through powder mixing, drying and screening, compaction and shaping, and sintering. The production process is simple, requiring no complex processes, and the raw materials are free of lead, rare earth elements, and precious metals, making them inexpensive and suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The scanning electron microscope images of the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramics prepared in Examples 1-4 and Comparative Example 1 and the corresponding grain size statistics;

[0028] Figure 2 X-ray diffraction patterns of sodium bismuth titanate-based lead-free relaxor ferroelectric ceramics prepared in Examples 1-4 and Comparative Example 1;

[0029] Figure 3 The dielectric thermograms of the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramics prepared in Examples 1-4 and Comparative Example 1;

[0030] Figure 4 PE single hysteresis loops of the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramics prepared in Examples 1-4 and Comparative Example 1 measured at 20° C. (standard atmospheric pressure) under respective maximum electric fields;

[0031] Figure 5 1 is a Weibull distribution diagram of the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramics prepared in Examples 1-4 and Comparative Example 1;

[0032] Figure 6 A comparison chart of the energy storage performance of sodium bismuth titanate-based lead-free relaxor ferroelectric ceramics prepared in Examples 1-4 and Comparative Example 1;

[0033] Figure 7 This is the PE single hysteresis loop of the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic prepared in Example 3 at 20° C. (standard atmospheric pressure) and an electric field of 200 kV / cm that varies with frequency;

[0034] Figure 8 The energy storage performance of the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic prepared in Example 3 at 20° C. (standard atmospheric pressure) and 200 kV / cm electric field varies with frequency;

[0035] Figure 9 The PE single hysteresis loop of the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic prepared in Example 3 changes with temperature at a frequency of 100 Hz and an electric field of 200 kV / cm;

[0036] Figure 10 This is a graph showing the energy storage performance of the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic prepared in Example 3 at a frequency of 100 Hz and an electric field of 200 kV / cm as a function of temperature;

[0037] Figure 11 The underdamping curve of the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic prepared in Example 3 at 20°C (standard atmospheric pressure) with electric field changes, the inset is I max Graph showing changes with electric field;

[0038] Figure 12 This is a graph showing the variation of current density and power density with electric field at 20° C. (standard atmospheric pressure) for the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic prepared in Example 3;

[0039] Figure 13 This is the overdamping curve of the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic prepared in Example 3 at 20° C. (standard atmospheric pressure) as the electric field changes;

[0040] Figure 14 This is a graph showing the variation of discharge energy storage density with electric field at 20° C. (standard atmospheric pressure) for the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic prepared in Example 3;

[0041] Figure 15 This is an impedance test analysis diagram of the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramics prepared in Examples 1-4 and Comparative Example 1 at 20°C (standard atmospheric pressure). Part of the circuit diagram in the figure is an equivalent circuit diagram. DETAILED DESCRIPTION

[0042] The present invention will be further described below in conjunction with specific examples, but should not be construed as limiting the present invention. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0043] Example 1

[0044] 1. Prepare analytically pure Na2CO3, Bi2O3, TiO2, SrCO3, ZrO2 and MgO powders at 0.91 (0.7 Na 0.5 Bi 0.5 TiO3-0.3Sr 0.7 Bi 0.2 TiO3)-0.09Bi(Mg 0.5 Zr 0.5 )O3 stoichiometric ratio was weighed, anhydrous ethanol was used as the medium, zirconium balls were added, and a planetary ball mill was used to mix at a speed of 250 rpm for 24 h. The obtained slurry was filtered through the zirconium balls and placed in an 80°C oven to dry and passed through a 40-mesh sieve to obtain ceramic powder.

[0045] 2. Pre-calcine the ceramic powder in a muffle furnace at 850°C for 3 hours to obtain a pre-calcined powder. Weigh 5g of the pre-calcined powder and add 5wt% of the binder polyvinyl butyral (PVB). Continue grinding to evenly mix the PVB and the above powder to obtain a viscous powder. This powder is then placed in a mold and axially pressed at 7MPa for 2 minutes to obtain a green body with a thickness of 1mm and a diameter of 10mm. This green body is then placed in a PP vacuum-sealed bag and pressurized at 200MPa for 5 minutes to obtain a ceramic green body.

[0046] 3. The ceramic green body was sintered in a muffle furnace in two steps. The temperature was first raised to 600℃ and kept for 6 hours, then raised to the highest temperature of 1180℃ and kept for 1 hour, and then lowered to 1120℃ and kept for 4 hours. After the furnace cavity cooled, 0.91(0.7Na 0.5 Bi 0.5 TiO3-0.3Sr 0.7 Bi 0.2 TiO3)-0.09Bi(Mg 0.5 Zr 0.5 )O3 ceramics, namely sodium bismuth titanate-based lead-free relaxor ferroelectric ceramics with high energy storage, have an energy storage density of 4.77 J / cm 3 , the energy storage efficiency is 78.41%.

[0047] Example 2

[0048] 1. Prepare analytically pure Na2CO3, Bi2O3, TiO2, SrCO3, ZrO2 and MgO powders at 0.88 (0.7 Na 0.5 Bi 0.5 TiO3-0.3Sr 0.7 Bi 0.2 TiO3)-0.12Bi(Mg 0.5 Zr 0.5)O3 stoichiometric ratio was weighed, anhydrous ethanol was used as the medium, zirconium balls were added and ball milled at 250 rpm in a planetary ball mill for 24 h to mix evenly, the obtained slurry was filtered through the zirconium balls and placed in an 80°C oven to dry and passed through a 40-mesh sieve to obtain ceramic powder.

[0049] 2. Pre-calcine the ceramic powder in a muffle furnace at 850°C for 3 hours to obtain a pre-calcined powder. Weigh 5g of the pre-calcined powder and add 5wt% polyvinyl butyral. Continue grinding and mixing to obtain a viscous powder. This powder is then placed in a mold and axially pressed at 7MPa for 2 minutes to obtain a green body with a thickness of 1mm and a diameter of 10mm. This green body is then placed in a PP vacuum-sealed bag and pressurized at 200MPa for 5 minutes to obtain a ceramic green body.

[0050] 3. The ceramic green body was sintered in a muffle furnace in two steps. The temperature was first raised to 600℃ and kept for 6 hours, then raised to the highest temperature of 1160℃ and kept for 1 hour, and then lowered to 1120℃ and kept for 4 hours. After the furnace cavity cooled, 0.88 (0.7Na 0.5 Bi 0.5 TiO3-0.3Sr 0.7 Bi 0.2 TiO3)-0.12Bi(Mg 0.5 Zr 0.5 )O3 ceramics, namely sodium bismuth titanate-based lead-free relaxor ferroelectric ceramics with high energy storage, have an energy storage density of 5.32 J / cm 3 , the energy storage efficiency is 76.84%.

[0051] Example 3

[0052] 1. Prepare analytically pure Na2CO3, Bi2O3, TiO2, SrCO3, ZrO2 and MgO powders at 0.85 (0.7 Na 0.5 Bi 0.5 TiO3-0.3Sr 0.7 Bi 0.2 TiO3)-0.15Bi(Mg 0.5 Zr 0.5 )O3 stoichiometric ratio was weighed, anhydrous ethanol was used as the medium, zirconium balls were added and ball milled at 250 rpm using a planetary ball mill for 24 h to mix evenly, the obtained slurry was filtered through the zirconium balls and then placed in an 80°C oven for drying and passed through a 40-mesh sieve to obtain ceramic powder.

[0053] 2. Pre-calcine the ceramic powder in a muffle furnace at 850°C for 3 hours to obtain a pre-calcined powder. Weigh 5g of the pre-calcined powder and add 5wt% polyvinyl butyral. Grind and mix thoroughly in a mortar to obtain a viscous powder. This powder is then placed in a mold and axially pressed at 7MPa for 2 minutes to obtain a green body with a thickness of 1mm and a diameter of 10mm. This green body is then placed in a PP vacuum-sealed bag and pressurized at 200MPa for 5 minutes to obtain a ceramic green body.

[0054] 3. The ceramic green body was sintered in a muffle furnace in two steps. The temperature was first raised to 600℃ and kept for 6 hours, then raised to the highest temperature of 1160℃ and kept for 1 hour, and then lowered to 1120℃ and kept for 4 hours. After the furnace cavity cooled, 0.85 (0.7Na 0.5 Bi 0.5 TiO3-0.3Sr 0.7 Bi 0.2 TiO3)-0.15Bi(Mg 0.5 Zr 0.5 )O3 ceramics, namely sodium bismuth titanate-based lead-free relaxor ferroelectric ceramics with high energy storage, have an energy storage density of 6.75 J / cm 3 , the energy storage efficiency is 79.44%.

[0055] Example 4

[0056] 1. Prepare analytically pure Na2CO3, Bi2O3, TiO2, SrCO3, ZrO2 and MgO powders at 0.82 (0.7 Na 0.5 Bi 0.5 TiO3-0.3Sr 0.7 Bi 0.2 TiO3)-0.18Bi(Mg 0.5 Zr 0.5 )O3 in a stoichiometric ratio was weighed, and zirconium balls were added to anhydrous ethanol as the medium. The mixture was then ball-milled for 24 hours to achieve uniformity. This was done using a planetary ball mill at 250 rpm. The resulting slurry was filtered through the zirconium balls, dried in an 80°C oven, and passed through a 40-mesh sieve to obtain a ceramic powder.

[0057] 2. Pre-calcine the ceramic powder in a muffle furnace at 850°C for 3 hours to obtain a pre-calcined powder. Weigh 5g of the pre-calcined powder and add 5wt% polyvinyl butyral. Grind and mix thoroughly in a mortar to obtain a viscous powder. This powder is then placed in a mold and axially pressed at 7MPa for 2 minutes to obtain a green body with a thickness of 1mm and a diameter of 10mm. This green body is then placed in a PP vacuum-sealed bag and pressurized at 200MPa for 5 minutes to obtain a ceramic green body.

[0058] 3. The ceramic green body was sintered in a muffle furnace in two steps. The temperature was first raised to 600℃ and kept for 6 hours, then raised to the highest temperature of 1140℃ and kept for 1 hour, and then lowered to 1120℃ and kept for 4 hours. After the furnace cavity cooled, 0.82 (0.7Na 0.5 Bi 0.5 TiO3-0.3Sr 0.7 Bi 0.2 TiO3)-0.18Bi(Mg 0.5 Zr 0.5 )O3 ceramics, namely sodium bismuth titanate-based lead-free relaxor ferroelectric ceramics with high energy storage, have an energy storage density of 5.40 J / cm 3 , the energy storage efficiency is 78.01%.

[0059] Comparative Example 1

[0060] 1. Analytical pure Na2CO3, Bi2O3, TiO2, SrCO3, ZrO2 and MgO powders were mixed at 0.7Na 0.5 Bi 0.5 TiO3-0.3Sr 0.7 Bi 0.2 TiO3 was weighed in a stoichiometric ratio, and zirconium balls were added using anhydrous ethanol as a medium. The mixture was ball milled at 250 rpm for 24 h to obtain a uniform mixture. The obtained slurry was filtered through the zirconium balls and then dried in an oven at 80°C. The mixture was sieved through a 40-mesh sieve to obtain ceramic powder.

[0061] 2. The ceramic powder was calcined in a muffle furnace at 850°C for 3 hours to obtain a pre-calcined powder. 86.12 g of the pre-calcined powder was added to 5 wt% of the binder polyvinyl butyral (PVB). The mixture was further ground in a mortar to obtain a viscous powder. The powder was then placed in a mold and axially pressed at 7 MPa for 2 minutes to obtain a green body with a thickness of 1 mm and a diameter of 10 mm. The green body was then placed in a PP vacuum-sealed bag and pressure-sealed at 200 MPa for 5 minutes to obtain a ceramic green body.

[0062] 3. The ceramic green body was sintered in a muffle furnace in two steps. The temperature was first raised to 600℃ and kept for 6 hours, then raised to the highest temperature of 1195℃ and kept for 1 hour, and then lowered to 1120℃ and kept for 4 hours. After the furnace cavity cooled, 0.7Na 0.5 Bi 0.5 TiO3-0.3Sr 0.7 Bi 0.2 TiO3 ceramics are lead-free relaxor ferroelectric ceramics based on sodium bismuth titanate. The energy storage density of this ceramic is 1.16 J / cm 3 , the energy storage efficiency is 71.44%.

[0063] The ceramics obtained in Examples 1-4 and Comparative Example 1 were ground thin, and gold electrodes were sputtered on both sides of the ceramics, and various electrical tests were performed. Figure 1 The scanning electron micrographs and corresponding grain size statistics of the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramics of Examples 1-4 and Comparative Example 1 are shown. (a)-(e) are scanning electron micrographs when x=0, 0.09, 0.12, 0.15, and 0.18, respectively; (f)-(j) are grain sizes when x=0, 0.09, 0.12, 0.15, and 0.18, respectively. Figure 1 It can be seen that the grain structure of all ceramics is uniform and dense with clearly discernible grain boundaries, and the average grain size is 1 to 3 μm, indicating that the relative density of the ceramics exceeds 97%. Figure 2 The room temperature X-ray diffraction patterns of the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramics of Examples 1-4 and Comparative Example 1 are shown. Figure 2 It can be seen that all ceramics do not contain other impurity phases of perovskite structure. In addition, with the increase of Bi(Mg 0.5 Zr 0.5 As the O3 content increases, the diffraction front near 45° shifts to lower diffraction angles, and the asymmetric single peak gradually evolves into a weak splitting front, indicating the coexistence of multiple phases. This is because magnesium and zirconium, with their large ionic radius, enter the crystal lattice and replace the original titanium. Figure 3 The dielectric temperature spectra of the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramics of Examples 1-4 and Comparative Example 1 are shown in FIG. Figure 3 It can be seen that the dielectric constant-temperature peak moves toward low temperature with the increase of frequency. It shows the characteristic linearity of typical relaxor ferroelectrics. At the same time, two dielectric abnormal peaks appear on the dielectric constant-temperature curve, namely the low temperature side peak (T s ) and high temperature side peak (T m The low temperature side peak is due to the thermal evolution of the polar nano-microregions of the rhombohedral phase (space group R3c) and tetragonal phase (space group P4bm). The high temperature side peak is due to the thermal evolution of the polar nano-microregions of the tetragonal phase. 0.5 Zr 0.5 )O3 content increases, T m The temperature shifts from 329°C to a low temperature of 266°C, indicating that all ceramics are close to relaxor ferroelectrics.

[0064] Figure 4 The PE single hysteresis loops of the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramics of Examples 1-4 and Comparative Example 1 were measured at 20°C (under standard atmospheric pressure) under the respective larger electric fields. Figure 4 It can be seen that as Bi(Mg 0.5 Zr 0.5)With the increase of the O3 content, the residual polarization intensity continues to decrease, while the saturation polarization intensity first increases and then decreases with the increase of x. The sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic of Example 3 reaches a maximum value, showing a typical relaxor ferroelectric hysteresis loop. Figure 5 The Weibull distribution diagram of the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramics of Examples 1-4 and Comparative Example 1 is shown in FIG. Figure 5 It can be seen that as Bi(Mg 0.5 Zr 0.5 As the )O3 content increases, the breakdown field strengths of the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramics of Examples 1-4 and Comparative Example 1 first increase and then decrease, with the maximum value occurring in the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic of Example 3. The slope β of Examples 1-4 is greater than 20, indicating that the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramics have good stability. Figure 6 The figure is a comparison of the energy storage performance of sodium bismuth titanate-based lead-free relaxor ferroelectric ceramics of Examples 1-4 and Comparative Example 1. Figure 6 It can be seen that the energy storage performance increases first and then decreases with the increase of x. The sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic of Example 3 (when x = 0.15) obtains 6.75 J / cm 3 The energy storage density and energy storage efficiency of 79.44% are achieved, resulting in the optimal energy storage performance.

[0065] Figure 7-8 The PE single hysteresis loop diagram and the corresponding energy storage performance diagram of the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic of Example 3 at 20°C (standard atmospheric pressure) and 200kV / cm electric field vary with frequency. Figure 7 and 8 It can be seen that in the frequency range of 1-120Hz, W rec The value is higher than 2.9J / cm 3 , and η is greater than 81%, indicating that the sodium bismuth titanate-based lead-free relaxor ferroelectric has excellent frequency stability. Figure 9-10 The PE single hysteresis loop diagram of the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic of Example 3 at 100 Hz and 200 kV / cm electric field as a function of temperature and the corresponding energy storage performance diagram are shown. Figure 9 and 10 It can be seen that the hysteresis loop presents a relatively slender shape in the range of 20~180℃ (under standard atmospheric pressure), which shows that the sodium bismuth titanate-based lead-free relaxor ferroelectric has typical relaxor ferroelectric characteristics and relatively stable temperature stability. Figure 11 The underdamping curve of the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic of Example 3 at 20°C (under standard atmospheric pressure) varies with the electric field, wherein the inset is I max With the electric field change diagram; Figure 11It can be seen that the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic of Example 3 has an extremely fast discharge rate under various electric fields at room temperature, and the fastest discharge rate reaches 49.1 nanoseconds under an electric field of 180 kV / cm.

[0066] Figure 12 The current density and power density of the lead-free relaxor ferroelectric ceramic based on sodium bismuth titanate of Example 3 at 20°C (under standard atmospheric pressure) vary with the electric field. Figure 12 It can be seen that the current density (C D ) and power density (P D ) increases with the increase of electric field and reaches the maximum value of 541.4 A / cm at 180 kV / cm. 2 and 48.73MW / cm 3 . Figure 13 The overdamping curve of the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic of Example 3 at 20°C (standard atmospheric pressure) varies with the electric field. Figure 13 It can be seen that the discharge current decay is not prominent and the oscillation plays a dominant role. If the resistance is larger, the decay will become significant and the discharge current oscillation will become unimportant. Figure 14 The graph of the discharge energy storage density of the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic of Example 3 at 20°C varies with the electric field. Figure 14 It can be seen that under an electric field of 180 kV / cm, the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic of Example 3 achieved an ultrafast discharge speed of 49.1 ns. At the same time, it achieved a discharge speed of 6.75 J / cm 3 The charge and discharge performance shows that the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic of the present invention has excellent energy storage performance and has great potential in practical applications. Figure 15 The impedance diagrams of the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramics of Examples 1-4 and Comparative Example 1 at 500°C and 100-2 MHz are shown. Part of the circuit diagram is an equivalent circuit diagram. Figure 15 As shown, the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic of Example 3 has the largest resistance, and the maximum grain boundary resistance obtained by fitting is 850890Ω. This shows that the increase in impedance and the decrease in oxygen vacancy concentration are beneficial to the improvement of the breakdown field strength of the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic.

[0067] The present invention obtains a material with excellent energy storage performance by changing the composition. The ceramic has good temperature stability, frequency stability, large saturation polarization intensity, low residual polarization intensity, and higher breakdown electric field strength. The energy storage density of the ceramic is 4.8J / cm 3 The energy storage efficiency is above 75%. Under the condition of room temperature and external electric field strength of 180kV / cm, the current density reaches 541.40A / cm2 , power density reaches 48.73MW / cm 3 , and an ultrafast discharge time of 49.1ns, which can be applied to high-power pulse devices.

[0068] The above embodiments are preferred implementations of the present invention, but the implementations of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A high energy storage sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic, characterized in that: The chemical formula of the ferroelectric ceramic is (1- x )(0.7Na 0.5 Bi 0.5 TiO3-0.3Sr 0.7 Bi 0.2 TiO3)- x Bi(Mg 0.5 Zr 0.5 )O3, of which 0.09< x ≤0.18; Na2CO3, Bi2O3, TiO2, SrCO3, ZrO2 and MgO are uniformly mixed to obtain ceramic powder, the ceramic powder is calcined at 845~855℃, and then naturally cooled in the furnace, a binder polyvinyl butyral is added to obtain a powder mass, and then axially pressed at a pressure of 5~10MPa to obtain a green body, and cold isostatic pressing is performed at 195~205MPa to obtain a ceramic body; the ceramic body is first heated to 595~605℃ and kept warm, then heated to 1130~1195℃ for sintering, and then cooled to 1000~1120℃ to obtain.

2. The sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic according to claim 1, characterized in that: The energy storage density of the ferroelectric ceramic is 4.7 J / cm 3 Above, the energy storage efficiency is above 75%.

3. The sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic according to claim 1, characterized in that: The chemical formula of the ferroelectric ceramic is (0.85)(0.7Na 0.5 Bi 0.5 TiO3-0.3Sr 0.7 Bi 0.2 TiO3)-0.15Bi(Mg 0.5 Zr 0.5 )O3.

4. The sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic according to claim 3, characterized in that: The energy storage density of the ferroelectric ceramic is 6.75 J / cm 3 , the energy storage efficiency is 79.44%.

5. The method for preparing the high energy storage sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. Na2CO3, Bi2O3, TiO2, SrCO3, ZrO2 and MgO are uniformly mixed to obtain a ceramic powder; S2. The ceramic powder is calcined at 845-855°C, then naturally cooled in the furnace. A binder, polyvinyl butyral, is added to form a powder mass. This mass is then axially pressed at a pressure of 5-10 MPa to form a green body. This is then cold isostatically pressed at a pressure of 195-205 MPa to obtain a ceramic body. S3. The ceramic body is first heated to 595-605°C and maintained at this temperature, then heated to 1130-1195°C for sintering, and then cooled to 1000-1120°C to obtain a high-energy-storage sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic.

6. The method for preparing the high energy storage sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic according to claim 5, characterized in that: The calcination time in step S2 is 3 to 4 hours, and the axial pressing time is 3 to 5 minutes.

7. The method for preparing the high energy storage sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic according to claim 5, characterized in that: The holding time in step S3 is 6 to 7 hours, and the sintering time is 4 to 5 hours.

8. Use of the high energy storage sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic according to any one of claims 1 to 4 in high power pulse devices.

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