High-energy-storage sodium bismuth titanate-based lead-free relaxor type ferroelectric ceramic as well as preparation method and application of high-energy-storage sodium bismuth titanate-based lead-free relaxor type ferroelectric ceramic

Abstract

The invention belongs to the technical field of ceramics, and discloses a high-energy-storage sodium bismuth titanate-based lead-free relaxation type ferroelectric ceramic as well as a preparation method and application thereof, the chemical formula of the ferroelectric ceramic is (1-x) (0.7 Na < 0.5 > Bi < 0.5 > TiO < 3 >-0.3 Sr < 0.7 > Bi < 0.2 > TiO < 3 >)-xBi (Mg < 0.5 > Zr < 0.5 >) O < 3 >, x is smaller than or equal to 0.18. The ceramic has relatively good temperature stability and frequency stability, relatively large saturation polarization intensity, relatively low remanent polarization intensity and relatively high breakdown-resistant electric field intensity. The energy storage density of the ferroelectric ceramic is 4.7 J / cm < 3 > or above, the energy storage efficiency is 75% or above, and the ferroelectric ceramic 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 scenes with large 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 through 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 of 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 field and higher P r As a result, the energy storage density and energy storage efficiency of the matrix are extremely low. Therefore, it is necessary to dope and modify sodium bismuth titanate ceramics to obtain a higher energy storage density and efficiency at a certain temperature, and also to obtain ceramics with excellent energy storage performance in a wide temperature range, which has important practical significance for the application in the field of electronic equipment at normal temperatures. Summary of the invention

[0009] In order to solve the above-mentioned deficiencies and shortcomings in the 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 intensity, low residual polarization intensity, higher breakdown electric field strength, and its energy storage density is 4.8 J / cm 3 Above, the energy storage efficiency is over 75%.

[0010] Another object of the present invention is to provide a method for preparing the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic. The method improves the energy storage density and efficiency by regulating the composition of the sodium bismuth titanate ceramic system, and at the same time makes it have good stability in a wide temperature range and frequency.

[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 TiO 3 -0.3Sr 0.7 Bi 0.2 TiO 3 )-xBi(Mg 0.5 Zr 0.5 ) 3 , 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 over 75%.

[0015] Preferably, the chemical formula of the ferroelectric ceramic is (0.85)(0.7Na 0.5 Bi 0.5 TiO 3 -0.3Sr 0.7 Bi 0.2 TiO 3 )-0.15Bi(Mg 0.5 Zr 0.5 ) 3 .

[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 method for preparing the high energy storage sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic comprises the following steps:

[0018] S1. Na 2 CO 3 、Bi 2 O 3 、TiO 2 、SrCO 3 、ZrO 2 and MgO uniformly mixed to obtain ceramic powder;

[0019] S2. The ceramic powder is calcined at 845-855°C, and then cooled naturally in the furnace, and a binder polyvinyl butyral is added (compared with common binders such as polyurethane and polyvinyl alcohol, it has a higher degree of ceramic bonding and leaves no residue during the furnace debinding process) to obtain a powder mass, and then axially pressed at a pressure of 5-10 MPa to obtain a green body, and 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 of electricity (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 TiO 3 -0.3Sr 0.7 Bi 0.2 TiO 3 )-xBi(Mg 0.5 Zr 0.5 ) 3 , Bi(Mg 0.5 Zr0.5 ) 3 The addition of makes the ceramic change from rhombic phase to tetragonal phase, and also makes the grain size smaller, the grain boundary density increases, and the ceramic is more dense, which will help to improve the breakdown field strength. The ceramic has good temperature stability, frequency stability, large saturation polarization strength, low residual polarization strength, higher breakdown electric field strength, and its energy storage density is 4.8J / cm 3 The energy storage efficiency is above 75%. 0.5 Zr 0.5 ) 3 The incorporation of leads to an increase in the tilting of oxygen octahedrons, which ultimately enhances the short-range structural disorder, induces nano-polar micro-regions, and further improves the relaxor properties of the material. The average breakdown field strength increases from 165.92 kV / cm in the matrix component (x=0) to 393.39 kV / cm in the preferred group (x=0.15), and decreases with the increase in the incorporation amount after the preferred group. The maximum ΔP (50.58 μC / cm) is obtained in the preferred 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 13.2%. Its temperature stability is excellent; in the frequency range of 1-200Hz, W rec The change is 12.6%, which proves its good frequency stability.

[0026] 2. The present invention obtains environmentally friendly, non-toxic, high energy storage performance lead-free ceramics through powder mixing, drying and screening, pressing and shaping, and sintering. The production process is simple, no difficult process requirements, the raw materials do not contain lead, rare earth elements and precious metals, the raw materials are cheap, and it is 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 4PE single hysteresis loops of the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramics obtained in Examples 1-4 and Comparative Example 1 measured at 20° C. (standard atmospheric pressure) under respective larger electric fields;

[0031] Figure 5 The 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 It is a comparison diagram 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 The PE single hysteresis loop of the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic prepared in Example 3 changes with frequency at 20° C. (standard atmospheric pressure) and an electric field of 200 kV / cm;

[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] Fig. 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] Fig.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] Fig.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 variation, and the inset is I max Graph of changes with electric field;

[0038] Fig.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] Fig.13 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] Fig.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] Fig.15 It 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), and part of the circuit diagram in the figure is an equivalent circuit diagram. DETAILED DESCRIPTION

[0042] The content of the present invention is further described below in conjunction with specific examples, but it should not be construed as limiting the present invention. If not specifically indicated, 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. Analytical pure Na 2 CO 3 、Bi 2 O 3 、TiO 2 、SrCO 3 、ZrO 2 and MgO powder at 0.91(0.7Na 0.5 Bi 0.5 TiO 3 -0.3Sr 0.7 Bi 0.2 TiO 3 )-0.09Bi(Mg 0.5 Zr 0.5 ) 3 The 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 250 rpm for 24 hours. The zirconium balls were filtered from the obtained slurry, and then placed in an oven at 80°C for drying and passed through a 40-mesh sieve to obtain ceramic powder.

[0045] 2. Pre-sinter the ceramic powder in a muffle furnace at 850°C for 3 hours to obtain pre-sintered powder. Weigh 5g of pre-sintered powder and add 5wt% of the binder polyvinyl butyral (PVB) to mix, continue grinding to mix the PVB and the above powder evenly to obtain a sticky powder, put it into a mold, and axially press it at 7MPa for 2min to obtain a green body with a thickness of 1mm and a diameter of 10mm, then put it into a PP vacuum sealed bag and keep it at 200MPa for 5min to obtain a ceramic green body.

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

[0047] Example 2

[0048] 1. Analytical pure Na 2 CO 3 、Bi 2 O 3 、TiO 2 、SrCO 3 、ZrO 2 and MgO powder at 0.88 (0.7Na 0.5 Bi 0.5 TiO 3 -0.3Sr 0.7 Bi 0.2 TiO 3 )-0.12Bi(Mg 0.5 Zr 0.5 ) 3 The stoichiometric ratio was weighed, anhydrous ethanol was used as the medium, zirconium balls were added, and the mixture was evenly mixed using a planetary ball mill at 250 rpm for 24 hours. The zirconium balls were filtered from the obtained slurry, and the mixture was placed in an oven at 80°C for drying and passed through a 40-mesh sieve to obtain ceramic powder.

[0049] 2. Pre-sinter the ceramic powder in a muffle furnace at 850°C for 3 hours to obtain pre-sintered powder. Weigh 5g of pre-sintered powder and add 5wt% of polyvinyl butyral, continue to grind and mix evenly to obtain sticky powder, put it into a mold, and axially press it at 7MPa for 2min to obtain a green body with a thickness of 1mm and a diameter of 10mm, then put it into a PP vacuum sealed bag and keep it at 200MPa for 5min to obtain a ceramic green body.

[0050] 3. The ceramic green body was sintered in a muffle furnace in two steps, first heated to 600℃ and kept for 6h, then heated to the highest temperature of 1160℃ and kept for 1h, then cooled to 1120℃ and kept for 4h. After the furnace cavity cooled, 0.88(0.7Na 0.5 Bi 0.5 TiO 3 -0.3Sr 0.7 Bi 0.2 TiO 3 )-0.12Bi(Mg 0.5 Zr0.5 ) 3 The ceramic is a high energy storage sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic with an energy storage density of 5.32 J / cm 3 , the energy storage efficiency is 76.84%.

[0051] Example 3

[0052] 1. Analytical pure Na 2 CO 3 、Bi 2 O 3 、TiO 2 、SrCO 3 、ZrO 2 and MgO powder at 0.85(0.7Na 0.5 Bi 0.5 TiO 3 -0.3Sr 0.7 Bi 0.2 TiO 3 )-0.15Bi(Mg 0.5 Zr 0.5 ) 3 The stoichiometric ratio was weighed, anhydrous ethanol was used as the medium, zirconium balls were added, and the mixture was evenly mixed using a planetary ball mill at 250 rpm for 24 hours. The obtained slurry was filtered to remove the zirconium balls, and then placed in an oven at 80°C for drying and passed through a 40-mesh sieve to obtain ceramic powder.

[0053] 2. Pre-sinter the ceramic powder in a muffle furnace at 850℃ for 3h to obtain pre-sintered powder. Weigh 5g of pre-sintered powder and add 5wt% of polyvinyl butyral, grind and mix in a mortar to obtain a sticky powder, put it into a mold, and press it at 7MPa for 2min to obtain a green body with a thickness of 1mm and a diameter of 10mm. Then put it into a PP vacuum sealed bag and press it at 200MPa for 5min to obtain a ceramic green body.

[0054] 3. The ceramic green body was sintered in a muffle furnace in two steps, first heated to 600℃ and kept for 6h, then heated to the highest temperature of 1160℃ and kept for 1h, then cooled to 1120℃ and kept for 4h. After the furnace cavity cooled, 0.85(0.7Na 0.5 Bi 0.5 TiO 3 -0.3Sr 0.7 Bi 0.2 TiO 3 )-0.15Bi(Mg 0.5 Zr 0.5 ) 3 The ceramic is a high energy storage sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic with an energy storage density of 6.75 J / cm3 , the energy storage efficiency is 79.44%.

[0055] Example 4

[0056] 1. Analytical pure Na 2 CO 3 、Bi 2 O 3 、TiO 2 、SrCO 3 、ZrO 2 and MgO powder at 0.82(0.7Na 0.5 Bi 0.5 TiO 3 -0.3Sr 0.7 Bi 0.2 TiO 3 )-0.18Bi(Mg 0.5 Zr 0.5 ) 3 The stoichiometric ratio was weighed, anhydrous ethanol was used as the medium, zirconium balls were added and mixed evenly by ball milling for 24 hours, and this step used a planetary ball mill at a speed of 250 rpm. The obtained slurry was filtered with zirconium balls, placed in an oven at 80°C for drying, and passed through a 40-mesh sieve to obtain ceramic powder.

[0057] 2. Pre-sinter the ceramic powder in a muffle furnace at 850℃ for 3h to obtain pre-sintered powder. Weigh 5g of pre-sintered powder and add 5wt% of polyvinyl butyral, grind and mix in a mortar to obtain a sticky powder, put it into a mold, and press it at 7MPa for 2min to obtain a green body with a thickness of 1mm and a diameter of 10mm. Then put it into a PP vacuum sealed bag and press it at 200MPa for 5min to obtain a ceramic green body.

[0058] 3. The ceramic green body was sintered in a muffle furnace in two steps, first heated to 600 ° C and kept for 6 hours, then raised to the highest temperature of 1140 ° C and kept for 1 hour, and then lowered to 1120 ° C and kept for 4 hours. After the furnace cavity was cooled, 0.82 (0.7Na 0.5 Bi 0.5 TiO 3 -0.3Sr 0.7 Bi 0.2 TiO 3 )-0.18Bi(Mg 0.5 Zr 0.5 ) 3 The ceramic is a high energy storage sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic with 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 Na 2 CO 3 、Bi 2 O 3 、TiO 2 、SrCO 3 、ZrO 2 and MgO powder according to 0.7Na 0.5 Bi 0.5 TiO 3 -0.3Sr 0.7 Bi 0.2 TiO 3 The stoichiometric ratio was weighed, anhydrous ethanol was used as the medium, zirconium balls were added, and a planetary ball mill was used to ball mill at 250 rpm for 24 hours to mix evenly. The obtained slurry was filtered to remove the zirconium balls and then placed in an oven at 80°C for drying, and passed through a 40-mesh sieve to obtain ceramic powder.

[0061] 2. The ceramic powder was placed in a muffle furnace and calcined at 850°C for 3 hours to obtain a pre-burned powder. 86.12g of the pre-burned powder was weighed and added with 5wt% of the binder polyvinyl butyral (PVB), and the powder was ground and mixed evenly in a mortar to obtain a sticky powder, which was put into a mold and axially pressed at 7MPa for 2min to obtain a green body with a thickness of 1mm and a diameter of 10mm, which was then put into a PP vacuum sealed bag and kept at 200MPa for 5min 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 was cooled, 0.7Na 0.5 Bi 0.5 TiO 3 -0.3Sr 0.7 Bi 0.2 TiO 3 The ceramic is a lead-free relaxor ferroelectric ceramic based on sodium bismuth titanate. The energy storage density of the 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 sodium bismuth titanate-based lead-free relaxor ferroelectric ceramics of Examples 1-4 and Comparative Example 1. (a)-(e) are scanning electron micrographs when x=0, 0.09, 0.12, 0.15, and 0.18, respectively, and (f)-(j) are grain sizes when x=0, 0.09, 0.12, 0.15, and 0.18, respectively. Figure 1It can be seen that the grain structure of all ceramics is uniform and dense with clear 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 in FIG. Figure 2 It can be seen that all ceramics do not contain perovskite structures with other impurities. 0.5 Zr 0.5 ) 3 As the content increases, the diffraction front near 45° moves to a lower diffraction angle, and the asymmetric single peak gradually evolves into a weak splitting front, and multi-phase coexistence occurs. This is because the magnesium and zirconium elements with large ionic radius enter the lattice and replace the original titanium element. 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 anomaly 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 structural 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 structural polar nano-microregions of the tetragonal phase. 0.5 Zr 0.5 ) 3 The content of T m The temperature changes from 329℃ to 266℃, 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 ) 3 As the content of increases, 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. Figure 5 It can be seen that as Bi(Mg 0.5 Zr 0.5 ) 3As the content of increases, the breakdown field strength of the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramics of Examples 1-4 and Comparative Example 1 increases first and then decreases, and the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic of Example 3 reaches a maximum value. 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 chart 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 under an electric field of 385 kV / 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 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 as a function of frequency and the corresponding energy storage performance diagram. 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 better 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 under 100 Hz, 200 kV / cm electric field and the corresponding energy storage performance diagram. Fig. 9 and 10 It can be seen that the hysteresis loop presents a relatively slender shape in the range of 20 to 180°C (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. Fig.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) as the electric field changes, wherein the inset is I max With the electric field change diagram; Fig.11 It 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] Fig.12 The current density and power density of the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic of Example 3 at 20°C (under standard atmospheric pressure) vary with the electric field. Fig.12 It can be seen that the current density (C D) and power density (P D ) increase with the increase of electric field and reach the maximum value of 541.4A / cm at 180kV / cm electric field. 2 and 48.73MW / cm 3 . Fig.13 The overdamping curve of the sodium bismuth titanate-based lead-free relaxor ferroelectric ceramic of Example 3 at 20°C (under standard atmospheric pressure) as the electric field changes. Fig.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. Fig.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. Fig.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, 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. Fig.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. Fig.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 of the components. 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 4.8 J / 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 / cm 2 , 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 implementation modes of the present invention, but the implementation modes 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 equivalent replacement methods and are included in the protection scope 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)-xBi(Mg 0.5 Zr 0.5 )O3, where 0 <x≤0.18。 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 over 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 to 855 ° C, 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 to 10 MPa to obtain a green body, and then cold isostatically pressed at 195 to 205 MPa to obtain a ceramic body; 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.

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 insulation 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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