Composite material for enhancing electrocaloric effect as well as construction method and application of composite material
By periodically alternating ferroelectric and relaxor materials on a crystal to form a superlattice structure, and combining this with computational simulation methods, the problem of insufficient material optimization in existing technologies has been solved, thereby enhancing the electrocaloric effect and improving the efficiency of cooling devices.
Patent Information
- Application Number
- CN202511338066.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-18
- Publication Date
- 2025-12-16
AI Technical Summary
The lack of universal and efficient material performance optimization schemes in existing technologies has limited the development of electric card refrigeration technology, and traditional methods have limited effectiveness and lack theoretical guidance.
By periodically alternating ferroelectric and relaxor materials in one crystal direction to form a superlattice structure, and combining first-principles calculations and Hamiltonian parameters, composite materials are designed to enhance the electrocaloric effect.
It significantly improves the adiabatic temperature change of the electrocaloric effect, enhances the efficiency of refrigeration devices, and provides theoretical guidance through computational simulation methods, saving resources and time.
Smart Images
Figure CN121152544A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of refrigeration devices, in particular to a composite material for enhancing electrocaloric effect and a construction method and application thereof. BACKGROUND
[0002] Under the background of increasingly severe global warming and energy consumption, efficient and environmentally friendly refrigeration technology is crucial. However, the high-pollution refrigerant and high-energy consumption problem of traditional gas compression refrigeration technology has become the main bottleneck of its development. Scientists are urgently seeking a new generation of solid-state refrigeration scheme, among which the electrocaloric refrigeration technology is emerging. This technology uses the reversible temperature change of special materials under the action of an electric field to achieve refrigeration, which has great potential for zero greenhouse gas emissions, high energy conversion efficiency, and compact equipment.
[0003] Since the discovery of the electrocaloric effect, a variety of materials with electrocaloric effect have been reported, such as PVDF-based polymer materials, BaTiO3 thin films, PbZr 0.95 Ti 0.05 O3 thin films, etc. Among them, PbSc 0.5 Ta 0.5 O3, Ba(Zr,Ti)O3, etc. Perovskite ferroelectric and relaxor ferroelectric materials have been found to have strong electrocaloric effect in a wide temperature range, and some refrigeration prototypes have been designed based on this. However, the academic and industrial communities still lack a universal and efficient material performance optimization scheme. Existing researches mostly focus on improving performance through traditional strategies such as element doping, compounding or regulating phase transition temperature, but these methods often have limited effect and are mostly "trial and error" exploration, lacking clear theoretical guidance. Developing a universal scheme to enhance the electrocaloric effect based on physical principles is crucial for the development of electrocaloric refrigeration technology. SUMMARY
[0004] In order to solve the above-mentioned deficiencies existing in the prior art, the purpose of the present application is to provide a composite material for enhancing electrocaloric effect and a construction method and application thereof, so as to enhance the electrocaloric effect of the composite material and improve the efficiency of the refrigeration device.
[0005] The technical scheme for solving the above technical problems of the present application is as follows: a composite material for enhancing electrocaloric effect is provided, which comprises a ferroelectric material and a relaxor material; the ferroelectric material and the relaxor material are periodically arranged alternately in one crystal direction of the crystal to form a superlattice structure.
[0006] Further, the ferroelectric material is a perovskite structure ferroelectric crystal material with spontaneous polarization at low temperature.
[0007] Further, the perovskite structure ferroelectric crystal material includes BaTiO3 and Pb(Sc,Ta,Ti)O3.
[0008] Further, the relaxor material is a perovskite structure relaxor ferroelectric material without spontaneous polarization or with small spontaneous polarization.
[0009] Further, the peroviskite structure relaxor ferroelectric material includes Ba(Ti,Zr)O3 and PbSc 0.5 Ta 0.5 O3.
[0010] The application provides a construction method of the composite material, comprising the following steps: (1) selecting a cell structure according to the elements and crystal structures contained in the selected ferroelectric material and relaxor material, and constructing a material cell structure; (2) obtaining the effective Hamiltonian parameters of the material cell structure in step (1) by using the first principle calculation; (3) constructing a supercell structure based on the effective Hamiltonian parameters in step (2), and arranging different atomic positions in the ferroelectric material region and the relaxor material region to construct a superlattice structure periodically arranged along one crystal direction.
[0011] The application further provides an application of the composite material in preparing a refrigeration device.
[0012] The application has the following beneficial effects: (1) the application promotes the formation of local dipole percolation clusters in the relaxor material by using the spontaneous polarization in the ferroelectric material and the periodic arrangement of the ferroelectric material and the relaxor material, thereby realizing the effective enhancement of the electrocaloric effect; (2) the application uses the method of calculation simulation to design the material and characterize the material performance, overcomes the blindness of the traditional "trial and error" experiment, provides theoretical guidance for the experiment, saves resources and time, and improves the efficiency of material design. BRIEF DESCRIPTION OF DRAWINGS
[0013] Figure 1 Fig. 1 is a structural schematic diagram of the composite material of the application; Figure 2 Fig. 4 is an adiabatic temperature change comparison diagram of BTO, BZT20 and BZT20 / BTO superlattice materials under the application of an electric field at 270 K. DETAILED DESCRIPTION
[0014] The following examples are only used to explain the application, and are not used to limit the scope of the application. The specific conditions are not marked in the examples, and are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not marked with the manufacturer, and are all conventional products that can be purchased on the market.
[0015] Embodiment: Taking Ba(Zr,Ti)O3 system as an example, a composite material with BaTi 0.8 Zr 0.2 O3 (BZT20) as a relaxor material and BaTiO3 (BTO) as a ferroelectric material is constructed, and the electrocaloric effect thereof is calculated. The specific steps are as follows: (1) Select the cell structure according to the elements and crystal structure contained in the selected ferroelectric material and relaxor material. The structures of BZT20 and BTO are both perovskite structures with the general formula ABO3, where A is Ba and B includes Ti and Zr. The cubic perovskite structure is selected as the reference phase. The cell of the reference phase contains 5 atoms, among which the B site is a mixed atom using virtual crystal approximation (VCA) to represent the average effect of Zr and Ti atoms mixed. The local mode corresponding to the lowest optical branch of the phonon spectrum Gamma point of BZT20 (u mode) and the local mode corresponding to the acoustic branch (v mode) are selected as the basis set of atomic displacement mode, and the cell structure is constructed; (2) The effective Hamiltonian parameters are obtained by first-principles calculation. In this embodiment, the first-principles calculation is realized by using VASP software. Cells with different atomic displacement modes are constructed, and the relationship between energy and atomic force with respect to atomic displacement is calculated. According to the analytical expression of the effective Hamiltonian, the numerical value of the parameter is obtained; (3) Build a supercell structure using ALFE-H software. In this embodiment, a 10x10x24 supercell is selected, corresponding to 12000 atoms. The selected supercell has periodic boundary conditions in three crystal directions (hereinafter referred to as x, y, z axes, corresponding to
[100] ,
[010] ,
[001] crystal directions of cubic system). The first 20 layers of the supercell along the z direction are arranged as relaxor layers (BZT20), and the last 4 layers are arranged as ferroelectric layers (BTO). Thus, a superlattice composed of alternating BZT20 relaxor layers and BTO ferroelectric layers along the z direction under periodic boundary conditions is formed, as shown in Figure 1 ; Because the B site in the relaxor layer BZT20 contains mixed sites of Zr and Ti, in order to avoid the influence of single atomic arrangement on the results, 24 different Zr / Ti atomic distributions are constructed, each of which is generated by using the pseudo-random number generator of the C++ standard library, and Zr accounts for 20%; (4) Calculate the temperature change of a series of material structures satisfying the above superlattice structure requirements with temperature using ALFE-H software. Using ALFE-H software, the structures of various different atomic arrangements generated above are simulated for cooling. In the calculation, the Metropolis Monte Carlo (MMC) algorithm is used, starting from 500 K, simulating 100000 scans at each temperature, with a step size of 10 K, and cooling to 10 K. The BZT20 and BZT20 / BTO superlattice structures use the parameters calculated in step 2 above, and the BTO structure uses the parameters provided in the literature [Physical Review B 52, 6301 (1995)]; (5) Calculate the temperature change of the system during the process of applying and removing the electric field adiabatically from the specified temperature using ALFE-H software. The supercell structure constructed in step (3) above is selected as the starting structure at the final structure at 270 K simulated in step (4), and a micro-canonical Monte Carlo simulation is performed. The initial temperature of the simulation is selected to be 270 K, and a uniform electric field along the <001> direction is applied under adiabatic conditions. The electric field strength gradually changes with the progress of the simulation, first slowly increasing from 0 to 12.0 MV / cm, and then gradually decreasing to 0. During the process of increasing and decreasing the electric field strength, the thermodynamic average value of the temperature is calculated at 24 evenly distributed electric field values.
[0016] Comparative Example 1: 24 BZT20 structures with different atomic arrangements were generated using the method of Example 1, with a supercell size of 12x12x12, corresponding to 8640 atoms.
[0017] Comparative Example 2: The supercell structure of BaTiO3 (BTO) was constructed using the method of Example 1, with a supercell size of 12x12x12, corresponding to 8640 atoms. Since there are no mixed sites in BTO, it is not necessary to construct supercells with different atomic arrangements.
[0018] The temperature change curve of the examples and comparative examples 1-2 with the change of electric field is shown in Figure 2 Figure 2 Only the temperature change during the increase of the electric field is shown, and the curve during the decrease of the electric field is basically coincident with the curve of the increase process shown. Figure 2 It can be seen that the temperature of BTO (super cell composed of pure ferroelectric material) rises rapidly at the initial stage, and then quickly tends to saturation, and the temperature increases at a slower rate with the increase of electric field intensity. At the maximum electric field intensity, the maximum adiabatic temperature change is 15.28 K. BZT20 (super cell composed of pure relaxor material) has a slow temperature rise at the initial stage of applying electric field, and as the electric field intensity increases, the adiabatic temperature change increases significantly at first and then gradually decreases with the increase of electric field intensity. At the maximum electric field intensity, the maximum adiabatic temperature change is 20.15 K. The adiabatic temperature change of BZT20 / BTO composite material with the change of electric field intensity is similar to that of BZT20, but the adiabatic temperature change rate at the later stage is significantly higher than that of BZT20, and finally the maximum adiabatic temperature change is 22.36 K at the maximum electric field intensity, which is 46.3% higher than that of BTO and 11.0% higher than that of BZT20. In the embodiment, BTO is a ferroelectric material, and in its ferroelectric phase, the polarization intensity increases limitedly with the increase of electric field intensity, so the strength of electrocaloric effect under large electric field is weak. BZT20 is a relaxor ferroelectric material, and although there are local dipoles, their arrangement is scattered, and there is no spontaneous polarization in the macroscopic view. Under the external electric field, the local dipoles in BZT20 change their direction and gradually point to the direction of the external electric field, and under a large electric field, a large macroscopic polarization intensity can be formed, so there is a large electrocaloric effect potential. According to previous research [Physical Review B 105, 054104 (2022)], under the driving of external electric field, when the percolation cluster of local dipoles is quickly formed, the electrocaloric coefficient of the system is the largest, corresponding to the maximum change rate of adiabatic temperature change with respect to electric field intensity. In the BZT20 / BTO superlattice structure, the ferroelectric material BTO has spontaneous polarization and reaches a state with larger spontaneous polarization faster under the external electric field. In the periodically arranged structure, BZT20 forms a percolation cluster faster under the influence of the two sides of the ferroelectric BTO, thereby producing a stronger electrocaloric effect.
[0019] In summary, the superlattice structure composite material constructed by the effective Hamiltonian method based on the first principle can effectively improve the adiabatic temperature change and significantly enhance the electrocaloric effect.
[0020] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.
Claims
1. A composite material for enhancing electrocardiographic effect, characterized in that, It includes ferroelectric materials and relaxor materials; the ferroelectric materials and relaxor materials are arranged in a periodic alternation in one crystal direction of the crystal to form a superlattice structure.
2. The composite material according to claim 1, characterized in that, The ferroelectric material is a perovskite-structured ferroelectric crystal material that exhibits spontaneous polarization at low temperatures.
3. The composite material according to claim 2, characterized in that, The perovskite-structured ferroelectric crystal materials include BaTiO3 and Pb(Sc,Ta,Ti)O3.
4. The composite material according to claim 1, characterized in that, The relaxor material is a perovskite-structured relaxor ferroelectric material that does not have spontaneous polarization or has low spontaneous polarization.
5. The composite material according to claim 4, characterized in that, The perovskite-structured relaxor ferroelectric material includes Ba(Ti,Zr)O3 and PbSc. 0.5 Ta 0.5 O3.
6. A method for constructing the composite material according to any one of claims 1-5, characterized in that, Includes the following steps: (1) Based on the elements and crystal structure contained in the selected ferroelectric and relaxor materials, select the cell structure and construct the material cell structure; (2) The effective Hamiltonian parameters of the material cell structure in step (1) are obtained by first-principles calculation; (3) Based on the effective Hamiltonian parameters of step (2), a supercell structure is constructed. By arranging different atomic occupancy sites in the ferroelectric material region and the relaxor material region, a superlattice structure with periodic alternation along a crystal direction is constructed.
7. The application of the composite material described in claims 1-5 in the preparation of refrigeration devices.