Method for screening single-phase high-energy-storage A-bit high-entropy additive

Abstract

The invention discloses a method for screening a single-phase high-energy-storage A-site high-entropy additive, which comprises the following steps of: 1, calculating tolerance factors t and A-site ion size difference delta of different ceramic systems, and preliminarily screening out a single-phase ceramic system from the different ceramic systems; 2, density functional theory calculation is conducted on the single-phase ceramic systems screened out in the step 1, the formation energy Ef of each single-phase ceramic system is obtained, the single-phase ceramic system with the maximum absolute value Ef of the formation energy is screened out, and the single-phase ceramic system is the single-phase high-energy-storage A-bit high-entropy additive; and 3, preparing the screened single-phase high-energy-storage A-bit high-entropy additive into a high-entropy ceramic sample based on traditional solid-phase sintering, and testing the performance so as to verify the accuracy of evaluation in the steps 1-2. According to the method, the A-site high-entropy additive with the optimal energy storage performance can be efficiently screened out, so that the development period is shortened, and material waste is reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of ceramic materials, and particularly relates to a method for screening single-phase high-energy-storage A-site high-entropy additives. BACKGROUND

[0002] With the increasing demand for high-performance energy storage capacitors in the fields of electronic information, aerospace, new energy vehicles and the like, how to effectively improve the energy density and energy storage efficiency of energy storage ceramics from the aspect of material design has become a key research direction. At present, researchers have proposed various performance optimization strategies for energy storage ceramics, including domain engineering, defect engineering, band gap engineering, grain engineering and super-conducting engineering. These methods have achieved remarkable results in improving energy storage density and optimizing energy efficiency ratio. However, the energy storage performance is affected by the coupling of multiple factors, and traditional methods still have limitations in achieving overall performance improvement.

[0003] In recent years, the new material design concept based on "entropy engineering" has been introduced into the field of energy storage ceramics and has become a research hotspot. High-entropy ceramics introduce multiple component elements into the crystal lattice, which can effectively control the lattice distortion and inhibit the generation of impurities, thereby improving the dielectric and ferroelectric properties.

[0004] At present, the application paths of high-entropy components mainly include two types: one is to design new energy storage ceramics based on high-entropy components, and the other is to modify traditional ceramic matrices by using high-entropy components as functional additives. Among them, the latter has been widely applied due to its strong process compatibility and flexible control advantages. For example, one study introduced Ba(Zr 0.5 Na 0.5 )TiO3-0.35SrTiO3 into the ceramic matrix 0.65(Bi 0.2 Ti 0.2 Sn 0.2 Hf 0.2 Ta 0.2 )O3 high-entropy additive, which increased the energy storage density of the ceramic material to 4.89J / cm 3 , and the energy storage efficiency reached 92.1%; another study introduced (Ba 0.2 Sr 0.2 Ca 0.2 Bi 0.2 Na 0.2 )TiO3 high-entropy component into the ceramic matrix, which effectively improved the energy storage efficiency of BiFeO3-based ceramics.

[0005] Although relevant research has verified the significant advantages of high-entropy additives in improving energy storage performance, there is still a lack of systematic research on the single-phase formation mechanism and component selection rules thereof, and in the actual research process, a large number of experiments need to be carried out to prepare a large number of ceramic samples, and then the performance of the ceramic samples is tested one by one to select the high-entropy additive with the optimal energy storage performance, resulting in a long development cycle and too much material waste. SUMMARY

[0006] The application aims to provide a method for screening single-phase high-energy storage A-site high-entropy additives, which can efficiently screen the A-site high-entropy additive with the optimal energy storage performance from a ceramic system composed of high-entropy perovskite oxides coexisting with multiple elements, thereby shortening the development cycle and reducing material waste.

[0007] The application is realized by the following technical scheme:

[0008] The application is realized by the following technical scheme:

[0009] Step 1, (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3, (Na 0.2 La 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3, (Li 0.2 La 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 and (Li 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 are respectively denoted as A1, A2, A3 and A4, and single-phase ceramic systems are preliminarily screened from A1, A2, A3 and A4 by calculating the tolerance factor t and the A-site ion size difference δ of A1, A2, A3 and A4;

[0010] Step 2, the single-phase ceramic systems screened in step 1 are respectively subjected to density functional theory calculation to obtain the formation energy E f of each single-phase ceramic system, and the single-phase ceramic system with the maximum absolute value |E f | of the formation energy (Na 0.2 La 0.2 Ba 0.2 Sr 0.2 Ca 0.2)TiO3, which is a single-phase high-energy A-site high-entropy additive;

[0011] Step 3, based on traditional solid-phase sintering, the single-phase ceramic system (Na 0.2 La 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 is prepared into a high-entropy ceramic sample and tested for performance to verify the accuracy of steps 1-2.

[0012] Further, the tolerance factor t and the A-site ion size difference δ of step 1 are respectively expressed by the formulae:

[0013]

[0014] In the formulae, and are the average ion radii of the A-site and B-site cations, respectively, and t is closer to 1, which is more conducive to forming a stable single-phase structure.

[0015]

[0016] In the formulae, N is the number of elements at the A-site or B-site, C i is the mole fraction of element i, R i is the ion radius of element i, and δ is smaller, which is more conducive to forming a stable phase structure.

[0017] Further, the specific process of step 2 is: using the Vienna first-principles simulation program VASP to perform density functional theory (DFT) calculations on the single-phase ceramic system screened in step 1, in which the plane wave energy cutoff value is set to 450 eV, and the convergence accuracy of total energy and residual force is set to 10 -4 eV and All structures are doped with a 5×5×2 supercell, and a 2×2×5 k-point grid is constructed based on the Monkhorst-Pack method to represent the Brillouin zone, so as to accurately calculate the formation energy E f of the single-phase ceramic system, which is expressed as:

[0018] E f = [E total -4μ(M1)-4μ(M2)-4μ(M3)-4μ(M4)-4μ(M5)-20μ(Ti)

[0019] -60μ(O)] / 100

[0020] In the formulae, M1, M2, M3, M4, and M5 represent different metal elements in the ceramic system, μ represents the chemical potential of each element, and E totalTotal energy of the ceramic system.

[0021] Further, the specific process of step 3 is: according to the chemical formula of A1, A2, A3 and A4, weigh the raw materials and mix, sequentially carry out one wet ball milling, drying, pre-sintering, second wet ball milling, drying, sieving and tabletting, then transfer to a tube furnace, heat to 1250 DEG C at a heating rate of 5 DEG C / min and keep for 4h, then cool to 500 DEG C at a cooling rate of 5 DEG C / min, and finally cool to room temperature with the furnace, to obtain high-entropy ceramics.

[0022] Further, the wet ball milling is carried out at a rotation speed of 350 r / min for 8h with the mass ratio of material:ball:alcohol being 1:1:0.8.

[0023] Further, the drying is carried out at 90 DEG C for 3h.

[0024] Further, the pre-sintering is carried out in a muffle furnace at 1000 DEG C for 4h.

[0025] Further, the sieving is carried out through a 120 mesh sieve.

[0026] Further, the tabletting is first dry-pressed at 35 MPa, and then cold isostatic pressed at 200 MPa.

[0027] The present application has the following beneficial technical effects:

[0028] 1) Efficiently screen high-entropy components, improve screening accuracy and scientificity: combine the tolerance factor and cation radius difference, two common empirical indicators, with first-principle density functional theory (DFT) calculation, systematically study the relationship between formation energy, lattice distortion degree and ceramic single-phase formation, evaluate the structural stability of high-entropy components, and build an element screening system with predictability and guidance, which greatly improves the scientificity and accuracy of component screening, significantly shortens the development cycle of new energy storage ceramic materials, and provides theoretical guidance for ceramic material design and composition optimization.

[0029] 2) Achieve theoretical-experimental closed-loop verification and improve material research and development efficiency: establish a three-stage closed-loop optimization path of "empirical preliminary screening-theoretical prediction-experimental verification", back-propagate experimental preparation parameters through calculation results, realize rapid verification and screening of material performance, and is suitable for high-entropy perovskite oxides with multiple elements coexisting, which can effectively reduce the problems of high experimental trial and error cost, long verification period and material waste in traditional energy storage ceramic development.

[0030] 3) Obtain new high-entropy additives with excellent performance and improve energy storage performance: through the screening process, (Na 0.2 La 0.2 Ba 0.2 Sr0.2 Ca 0.2 )TiO3 as a single-phase A-site high-entropy additive, as a high-entropy oxide of a kind of linear material, has a fine hysteresis loop, and the energy storage density reaches 3.83 J / cm 3 at 430 kV / cm electric field, the energy storage efficiency reaches 94.4%, and shows good application potential.

[0031] 4) Promote the development of high-entropy energy storage ceramic material design system: the screening method has good scalability and universality, provides a standardized technical path for the component design of different system high-entropy energy storage ceramics, and has an important promoting effect on the performance improvement of energy storage capacitors, energy management elements and other key devices. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 XRD pattern of the high-entropy perovskite compound pre-fired in the present application examples 1-4;

[0033] Figure 2 XRD pattern of the single-phase high-entropy ceramic prepared in the present application examples 1-3;

[0034] Figure 3 Structure schematic diagram and lattice distortion degree comparison of the high-entropy ceramic prepared in the present application examples 2 and 4;

[0035] Fig. 4(a) is the hysteresis loop of the high-entropy ceramic prepared in the present application example 2 under different electric fields;

[0036] Fig. 4(b) is the maximum polarization intensity, residual polarization intensity and polarization difference of the high-entropy ceramic prepared in the present application example 2 under different electric fields;

[0037] Fig. 4(c) is the energy storage density and energy storage efficiency of the high-entropy ceramic prepared in the present application example 2 under different electric fields;

[0038] Figure 5 The energy storage density and efficiency values of the high-entropy ceramic prepared in the present application example 2 and the currently reported equimolar ratio high-entropy perovskite ceramic are compared. DETAILED DESCRIPTION

[0039] The present application will be further described in detail below in combination with specific examples, which are an explanation of the present application rather than a limitation.

[0040] The ceramic system (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3, (Na0.2 La 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3、(Li 0.2 La 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 and (Li 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 are denoted as A1, A2, A3 and A4 respectively. The calculation formulas of the tolerance factors t of A1, A2, A3 and A4 and the A-site ion size difference δ are expressed as follows:

[0041]

[0042] Where, and are the average ionic radius of the cations at the A and B sites, respectively. The closer t is to 1, the more conducive it is to the formation of a stable single-phase cubic or nearly cubic perovskite structure;

[0043]

[0044] Where N is the number of elements in position A or B, C i is the mole fraction of element i, R i is the ionic radius of element i. The smaller δ is, the more stable the phase structure is formed.

[0045] The alcohol used in the wet ball milling of the present invention is an ethanol aqueous solution with a mass fraction of 75%.

[0046] Example 1

[0047] Step 1. Calculate (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 tolerance factor t and A-site ion size difference δ are: t = 0.997; δ = 6.8%;

[0048] Step 2: Use Vienna Ab initio Simulation Package (VASP) to simulate (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2)TiO3 was subjected to density functional theory (DFT) calculations. During the simulation, a plane wave energy cutoff of 450 eV was used to improve the convergence of the calculation. At the same time, the convergence accuracy of the total energy and residual force reached 10 -4 eV and All structures are doped with a 5×5×2 supercell, and a 2×2×5 special k-point grid is constructed based on the Monkhorst-Pack method to represent the Brillouin zone, so as to achieve accurate calculation of the electronic structure and energy characteristics, and then calculate (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 formation energy E f , to form energy E f The absolute value of |E f | As a measure of phase stability, thus predicting the single-phase stability of ceramic systems, E f The calculation formula is expressed as:

[0049] E f =[E total -4μ(Na)-4μ(Bi)-4μ(Ba)-4μ(Sr)-4μ(Ca)-20μ(Ti)

[0050] -60μ(O)] / 100

[0051] Where μ is the chemical potential of each element, E total for (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )The total energy of TiO3, after calculation, E f =-7.588eV / atom;

[0052] Step 3: Preparation of high entropy ceramics (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3, the specific process is:

[0053] Step 3.1, according to the chemical formula (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2TiO3, respectively, and then mixed. First, the mixture was wet planetary ball milled at a speed of 350 r / min for 8 h with a mass ratio of material: ball: alcohol being 1:1:0.8, and then dried in an oven at 90 °C for 3 h to obtain a mixture;

[0054] Step 3.2, the mixture was briquetted and pre-sintered in a muffle furnace at 1000 °C for 4 h. Then, the mixture was wet planetary ball milled at a speed of 350 r / min for 8 h with a mass ratio of material: ball: alcohol being 1:1:0.8, and then dried in an oven at 90 °C for 3 h to obtain a mixture of (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3;

[0055] Step 3.3, the (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 powder was dry-pressed at 35 MPa and then cold isostatic pressed at 200 MPa to obtain a green ceramic body with a diameter of 10 mm and a thickness of 11 mm;

[0056] Step 3.4, the green ceramic body was placed in an alumina crucible with a zirconia pad, and the alumina crucible was placed in a box furnace. The temperature was raised to 1250 °C at a rate of 5 °C / min and maintained for 4 h, and then the temperature was lowered to 500 °C at a rate of 5 °C / min, and finally the furnace was cooled to room temperature, to obtain high-entropy ceramic (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3.

[0057] Example 2

[0058] Step 1, the tolerance factor t and the difference in A-site ion size δ of (Na 0.2 La 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 were calculated, and were 0.997 and 6.8%, respectively;

[0059] Step 2, the Vienna ab initio simulation package (VASP) was used to simulate (Na 0.2 La 0.2 Ba 0.2 Sr 0.2Ca 0.2 )TiO3 was subjected to density functional theory (DFT) calculations. During the simulation, a plane wave energy cutoff of 450 eV was used to improve the convergence of the calculation. At the same time, the convergence accuracy of the total energy and residual force reached 10 -4 eV and All structures are doped with a 5×5×2 supercell, and a 2×2×5 special k-point grid is constructed based on the Monkhorst-Pack method to represent the Brillouin zone, so as to achieve accurate calculation of the electronic structure and energy characteristics, and then calculate (Na 0.2 La 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 formation energy E f , to form energy E f The absolute value of |E f | As a measure of phase stability, thus predicting the single-phase stability of ceramic systems, E f The calculation formula is expressed as:

[0060] E f =[e total -4μ(Na)-4μ(La)-4μ(Ba)-4μ(Sr)-4μ(Ca)-20μ(Ti)

[0061] -60μ(O)] / 100

[0062] Where μ is the chemical potential of each element, E total for (Na 0.2 La 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )The total energy of TiO3, after calculation, E f =-7.83eV / atom;

[0063] Step 3: Preparation of high entropy ceramics (Na 0.2 La 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3, the specific process is:

[0064] Step 3.1, according to the chemical formula (Na 0.2 La 0.2 Ba 0.2 Sr 0.2 Ca 0.2)TiO3, respectively, and then mixed. First, the mixture was wet planetary ball milled at a speed of 350 r / min for 8 h with a mass ratio of material: ball: alcohol being 1:1:0.8, and then dried in an oven at 90℃ for 3 h to obtain a mixture;

[0065] Step 3.2, the mixture was briquetted and pre-sintered in a muffle furnace at 1000℃ for 4 h. Then, the mixture was wet planetary ball milled at a speed of 350 r / min for 8 h with a mass ratio of material: ball: alcohol being 1:1:0.8, and then dried in an oven at 90℃ for 3 h, and then sieved through a 120 mesh sieve to obtain a(Na 0.2 La 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3powder;

[0066] Step 3.3, the(Na 0.2 La 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3powder was dry-pressed at 35 MPa and then cold isostatic pressed at 200 MPa to obtain a green ceramic body with a diameter of 10 mm and a thickness of 11 mm;

[0067] Step 3.4, the green ceramic body was placed in an alumina crucible with a zirconia pad, and the alumina crucible was placed in a box furnace. The temperature was raised to 1250℃ at a rate of 5℃ / min and maintained for 4 h, and then the temperature was lowered to 500℃ at a rate of 5℃ / min, and finally the furnace was cooled to room temperature. A high-entropy ceramic(Na 0.2 La 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3was obtained.

[0068] Example 3

[0069] Step 1, the tolerance factor t and the difference in A-site ion size δ of(Li 0.2 La 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3were calculated, respectively, as follows: t = 0.964; δ = 17.08%;

[0070] Step 2, a high-entropy ceramic(Li 0.2 La 0.2 Ba 0.2 Sr 0.2 Ca 0.2)TiO3, the specific process is as follows:

[0071] Step 2.1, according to the chemical formula (Li 0.2 La 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3, TiO2, BaCO3, Li2CO3, SrCO3, CaCO3 and La2O3 are weighed respectively and mixed, first wet planetary ball milling at a speed of 350 r / min for 8 h with the mass ratio of material: ball: alcohol being 1:1:0.8, then drying in an oven at 90℃ for 3 h to obtain a mixture;

[0072] Step 2.2, the mixture is pressed into a block and placed in a muffle furnace, pre-sintering at 1000℃ for 4 h, then wet planetary ball milling at a speed of 350 r / min for 8 h with the mass ratio of material: ball: alcohol being 1:1:0.8, followed by drying in an oven at 90℃ for 3 h, and then sieving through a 120 mesh sieve to obtain (Li 0.2 La 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 powder;

[0073] Step 2.3, the (Li 0.2 La 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 powder is dry-pressed at 35 MPa and then cold isostatic pressed at 200 MPa to obtain a ceramic green body with a diameter of 10 mm and a thickness of 11 mm;

[0074] Step 2.4, the ceramic green body is placed in an alumina crucible with zirconia as the pad plate, and the alumina crucible is placed in a box furnace, heated to 1250℃ at a rate of 5℃ / min and kept for 4 h, then cooled to 500℃ at a rate of 5℃ / min, and finally cooled to room temperature with the furnace, to obtain high-entropy ceramic (Li 0.2 La 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3.

[0075] Example 4

[0076] Step 1, calculating (Li 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2)TiO3 tolerance factor t and A-site ion size difference δ are: t = 0.964; δ = 17.7%;

[0077] Step 2: Use Vienna first principle simulation program (VASP) to simulate (Li 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 was subjected to density functional theory (DFT) calculations. During the simulation, a plane wave energy cutoff of 450 eV was used to improve the convergence of the calculation. At the same time, the convergence accuracy of the total energy and residual force reached 10 -4 eV and All structures are doped with a 5×5×2 supercell, and a 2×2×5 special k-point grid is constructed based on the Monkhorst-Pack method to represent the Brillouin zone, so as to achieve accurate calculation of the electronic structure and energy characteristics, and then calculate (Li 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 formation energy E f , to form energy E f The absolute value of |E f | As a measure of phase stability, thus predicting the single-phase stability of ceramic systems, E f The calculation formula is expressed as:

[0078] E f =[E total -4μ(Li)-4μ(Bi)-4μ(Ba)-4μμ(Sr)-4μ(Ca)-20μ(Ti)-60μ(O)] / 100

[0079] Where μ is the chemical potential of each element, E total for (Li 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )The total energy of TiO3, after calculation, E f =-7.577eV / atom;

[0080] Step 3: Preparation of high entropy ceramics (Li 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3, the specific process is:

[0081] Step 3.1, according to the chemical formula (Li 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3, respectively, TiO2, BaCO3, Li2CO3, SrCO3, CaCO3 and Bi2O3 were weighed and mixed, first with a mass ratio of material: ball: alcohol of 1:1:0.8, wet planetary ball milling at a speed of 350 r / min for 8 h, then placed in an oven at 90℃ for 3 h to dry, to obtain a mixture;

[0082] Step 3.2, the mixture was pressed into a block and placed in a muffle furnace at 1000℃ for 4 h, then wet planetary ball milling at a speed of 350 r / min for 8 h with a mass ratio of material: ball: alcohol of 1:1:0.8, followed by drying in an oven at 90℃ for 3 h, and then sieved through a 120 mesh sieve to obtain (Li 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 powder;

[0083] Step 3.3, the (Li 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 powder was dry pressed at 35 MPa and then cold isostatic pressed at 200 MPa to obtain a ceramic green body with a diameter of 10 mm and a thickness of 11 mm;

[0084] Step 3.4, the ceramic green body was placed in an alumina crucible with zirconia as the pad, and the alumina crucible was placed in a box furnace, heated to 1250℃ at a rate of 5℃ / min and held for 4 h, then cooled to 500℃ at a rate of 5℃ / min, and finally cooled to room temperature with the furnace, to obtain high-entropy ceramic (Li 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3.

[0085] In order to more intuitively compare, the tolerance factor t and the difference in A-site ion size δ of the four ceramic systems A1, A2, A3 and A4 calculated in Step 1 of Examples 1-4 are listed in Table 1;

[0086] Table 1: Single-phase formation, tolerance factor and cation valence difference of four ceramic systems

[0087]

[0088] From Table 1, the tolerance factor t of the ceramic systems A1 and A2 of Example 1 and Example 2 is closer to 1, and the A-site ion size difference δ is also the smallest. It can be preliminarily judged that the ceramic systems A1 and A2 of Example 1 and Example 2 are most likely to form a stable single-phase cubic or approximately cubic perovskite structure; whether the ceramic systems A3 and A4 of Example 3 and Example 4 can form a stable single-phase cubic or approximately cubic perovskite structure cannot be determined yet.

[0089] In order to further screen the ceramic system capable of forming the most stable single-phase perovskite compound from the ceramic systems A1 and A2, the formation energy of A1 and A2 needs to be calculated respectively. At the same time, in order to verify whether the ceramic system A3 and A4 can form a stable single-phase perovskite structure, the formation energy of A4 is taken as an example. The formation energies E f are calculated for Example 1, Example 2 and Example 4 for comparison.

[0090] Table 2: Formation energy (E f ) of ceramic systems A1, A2 and A4

[0091]

[0092] As can be seen from Table 2, the absolute values of the formation energies of the ceramic systems A1 and A2 of Example 1 and Example 2 are higher than the absolute value of the formation energy of the ceramic system A4 of Example 4, and the absolute value |E f | of the formation energy of A2 is the highest, and the greater the absolute value |E f | of the formation energy, the higher the thermodynamic stability of the system. Therefore, it is indicated that A1 and A2 can form a stable single-phase structure, and A4 cannot form a single-phase structure. This trend matches the experimental results of step 1. In addition, it is also indicated that the ceramic system A2 of Example 2 can form the most stable single-phase perovskite compound.

[0093] In order to verify the accuracy of the above evaluation, the ceramic systems of Example 1 to Example 4 are prepared into high-entropy ceramic samples by traditional solid-phase sintering. The phase structure of the ceramic samples is characterized by X-ray diffractometer (XRD). The XRD test uses Cu-Kα target, and the test parameters are as follows: scanning step 0.02°, scanning speed 5° / min, tube current 40 mA, tube voltage 40 kV, scanning range 20-80°, X-ray incident wavelength 0.15418 n, and the results are shown in Figure 1 and Figure 2 , wherein: Figure 1The XRD patterns of the ceramic samples of Examples 1-4 after pre-sintering at 1000℃ can be seen that the ceramic systems A1, A2 and A3 of Examples 1-3 can synthesize single-phase structure, and the ceramic system A4 of Example 4 has obvious secondary phase; Figure 2 The XRD patterns of the high-entropy ceramics of Examples 1-3 after sintering at 1250℃ can be seen that the main characteristic peaks of the samples match the standard PDF card of cubic phase SrTiO3(PDF #86-0719); the analysis results by XRD show that the tolerance factor t, the size difference δ of A-site ions and the formation energy of the calculated ceramic system can effectively screen out the ceramic system capable of synthesizing single-phase perovskite compounds.

[0094] Figure 3 The structural schematic diagram of the high-entropy ceramic samples prepared in Examples 2 and 4 and the comparison of the degree of lattice distortion can be obviously observed that Na + and Li + occupy the A position of the ABO3 structure, accompanied by lattice shift, wherein the shift degree of Li + is greater than that of Na + , so the degree of structural distortion is more serious, thus it can be inferred that the serious lattice distortion is an important reason why the ceramic system A4 of Example 4 cannot synthesize single-phase structure, and the serious structural distortion is not conducive to improving the energy storage performance of the material, because in the multi-atomic system energy storage ceramic, lattice distortion is one of the common structural characteristics, which is usually caused by factors such as A / B site ion radius mismatch and electronegativity difference, so that the ions deviate from the ideal position, thereby enhancing the local polarization, and the moderate distortion can improve the maximum polarization strength of the material and enhance the relaxor ferroelectric effect, thereby improving its energy storage density, therefore, in the high-entropy ceramic system, the lattice distortion effect on the structure endows it with more excellent ferroelectric properties, however, the greater the degree of lattice distortion is not necessarily the better, excessive distortion may lead to the increase of lattice energy, thereby reducing the thermodynamic stability of the structure, making the material easy to precipitate secondary phase, thereby affecting the formation of single-phase structure, in addition, excessive distortion may also lead to local stress concentration, increase charge trapping and defect activity, thereby increasing dielectric loss and reducing the energy storage efficiency of the material.

[0095] The high-entropy ceramic (Na 0.2 La 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 sample prepared in Example 2 was polished to a thickness of 0.2mm by using sandpaper with different mesh, and after ultrasonic cleaning, a gold electrode with a diameter of 0.2mm was sputtered on both sides, so as to test its energy storage performance, in the test process, a sinusoidal alternating electric field was applied, and the scanning frequency was set to 10Hz, and the results are as follows Figures 4(a) to 4(c)As shown in the figure, wherein: from figure 4(a), it can be seen that the hysteresis loop under different electric fields always keeps the slender shape; from figure 4(b), it can be observed that with the increase of electric field intensity, the remanent polarization intensity always keeps at a low level and has no obvious change, and the maximum polarization intensity gradually increases with the increase of electric field; from figure 4(c), it can be seen that the energy storage density of 3.83J / cm3 and the energy storage efficiency of 94.4% are obtained at 440kV / cm.

[0096] The high-entropy ceramic prepared in example 2 is compared with the existing energy storage performance of the equimolar high-entropy perovskite structure ceramic, and the results are shown in Figure 5 As can be seen from the figure, compared with other ceramic materials, the energy storage density and efficiency of the high-entropy ceramic prepared in example 2 have advantages, which can be used as a kind of linear A-site high-entropy additive, and can effectively improve the energy storage performance of the ceramic.

[0097] The present application firstly calculates the tolerance factor t and the size difference δ of A-site ions of different ceramic systems, preliminarily selects the perovskite compounds capable of forming single-phase structure, and then calculates the formation energy E f Finally, the perovskite compounds with good stability and single-phase structure are selected, without sintering each ceramic system into a high-entropy ceramic sample and testing the performance, the A-site high-entropy additive can be screened, which is of great benefit to shorten the development cycle and reduce material waste.

Claims

1. A method for screening single-phase high energy storage A-site high entropy additives, characterized in that: The steps include: Step 1, Design (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3、(Na 0.2 La 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3、(Li 0.2 La 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 and (Li 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 ) Four TiO3 ceramic systems are denoted as A1, A2, A3 and A4 respectively. By calculating the tolerance factor t and the A-site ion size difference δ of A1, A2, A3 and A4, single-phase ceramic systems are preliminarily screened out from A1, A2, A3 and A4. Step 2: Perform density functional theory calculations on the single-phase ceramic systems selected in step 1 to obtain the formation energy E of each single-phase ceramic system. f , filter out the absolute value of formation energy |E f |The largest single-phase ceramic system (Na 0.2 La 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3, which is a single-phase high energy storage A-site high entropy additive; Step 3: Based on the traditional solid phase sintering, the selected single-phase ceramic system (Na 0.2 La 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 was prepared into high entropy ceramic samples and the performance was tested to verify the accuracy of the evaluation in steps 1 and 2.

2. The method for screening a single-phase high energy storage A-site high entropy additive according to claim 1, characterized in that: The tolerance factor t and the A-site ion size difference δ in step 1 are respectively expressed as follows: Where, and are the average ionic radius of the cations at the A and B sites, respectively. The closer t is to 1, the more conducive it is to forming a stable single-phase structure; Where N is the number of elements in position A or B, C i is the mole fraction of element i, R i is the ionic radius of element i. The smaller δ is, the more stable the phase structure is formed.

3. The method for screening a single-phase high energy storage A-site high entropy additive according to claim 1, characterized in that: The specific process of step 2 is: using the Vienna first principle simulation program VASP to perform density functional theory DFT calculations on the single-phase ceramic system selected in step 1, in this process, the plane wave energy cutoff value is set to 450eV, and the convergence accuracy of the total energy and residual force is set to 10 -4 eV and All structures were doped using a 5×5×2 supercell, and a 2×2×5 k-point grid was constructed based on the Monkhorst-Pack method to represent the Brillouin zone, thereby accurately calculating the formation energy E of the single-phase ceramic system. f , expressed as: E f =[E total -4μ(M1)-4μ(M2)-4μ(M3)-4μ(M4)-4μ(M5)-20μ(Ti) -60μ(O)] / 100 Where M1, M2, M3, M4 and M5 represent different metal elements in the ceramic system, μ represents the chemical potential of each element, and E total Represents the total energy of the ceramic system.

4. The method for screening a single-phase high energy storage A-site high entropy additive according to claim 1, characterized in that: The specific process of step 3 is as follows: according to the chemical formulas of A1, A2, A3 and A4, the raw materials are weighed and mixed, and wet ball milling, drying, pre-calcining, secondary wet ball milling, drying, screening and tableting are carried out in sequence. Then, the raw materials are transferred to a tube furnace, heated to 1250°C at a heating rate of 5°C / min and kept at this temperature for 4 hours, then cooled to 500°C at a cooling rate of 5°C / min, and finally cooled to room temperature in the furnace to obtain a high-entropy ceramic.

5. The method for screening a single-phase high energy storage A-site high entropy additive according to claim 4, characterized in that: The wet ball milling is carried out at a mass ratio of material: ball: alcohol of 1:1:0.8 and a rotation speed of 350 r / min for 8 hours.

6. The method for screening a single-phase high energy storage A-site high entropy additive according to claim 4, characterized in that: The drying is carried out at 90° C. for 3 hours.

7. The method for screening a single-phase high energy storage A-site high entropy additive according to claim 4, characterized in that: The pre-calcination is carried out in a muffle furnace at 1000° C. for 4 hours.

8. The method for screening a single-phase high energy storage A-site high entropy additive according to claim 4, characterized in that: The sieving is through a 120-mesh sieve.

9. The method for screening a single-phase high energy storage A-site high entropy additive according to claim 4, characterized in that: The tablets are firstly dry pressed at 35 MPa and then cold isostatically pressed at 200 MPa.

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