A method for regulating the magnetocaloric properties of a first-order phase-change magnetic refrigeration material by controlling the length of covalent bonds

Abstract

A method for regulating the magnetocaloric properties of a first-order phase-change magnetic refrigeration material by controlling the length of a covalent bond relates to the field of magnetocaloric properties. The invention can regulate the Curie temperature (T) of a first-order phase-change magnetic refrigeration material by controlling the length of a covalent bond. C ) and thermal hysteresis (ΔT hys ). This method is simple, convenient and effective. By adjusting the element ratio or doping other elements to affect the covalent bond length, the magnetocaloric properties of the material can be changed. This provides an effective way to study the design of components of magnetic refrigeration materials and improve magnetocaloric properties in the future.

Description

Technical Field

[0001] The invention relates to the field of magnetocaloric properties, and is a method for regulating the magnetocaloric properties of a magnetic refrigeration material with a primary phase change by controlling the length of a covalent bond. Background Art

[0002] In recent years, the increasingly serious environmental problems have received widespread attention from the international community. Among the many environmental problems, the increasingly serious greenhouse effect and the ozone hole should be paid special attention to. The greenhouse effect will not only lead to global warming and sea level rise, but also slow down the ocean currents that bring cold and hot air. The ozone hole will cause harmful ultraviolet rays to enter the atmosphere. The culprits of the greenhouse effect are Freon and chlorofluorocarbons, which are essential refrigerants in traditional mechanical compression refrigeration. Magnetic refrigeration technology is to refrigerate by making the magnetic working fluid undergo phase change and the heat change generated before and after the phase change through heat conduction. This technology has the advantages of high efficiency and energy saving, long life, high reliability, easy maintenance, low vibration and noise, and environmental friendliness. It is one of the most promising new refrigeration technologies to replace traditional gas compression refrigeration in the 21st century.

[0003] Although materials with first-order phase transition have large entropy values, they have large thermal hysteresis (ΔT hys ) will lead to energy loss and affect its refrigeration capacity; and the Curie temperature (T C ), which determines the temperature range in which it works. Many researchers have adjusted the Curie temperature and thermal hysteresis of magnetic refrigeration materials by adjusting the element ratio and doping with other elements.

[0004] However, blindly adjusting components and doping with new elements will increase the workload of scientific researchers and reduce efficiency. We understand the changes in magnetocaloric properties from the perspective of covalent bonds within the material crystals. Through systematic research, we discovered and established the intrinsic relationship between magnetocaloric properties and the length of covalent bonds. We have achieved the regulation of magnetocaloric properties by controlling the length of covalent bonds, thus forming a new method for finding suitable material components. Summary of the invention

[0005] The purpose of the present invention is to provide an effective way to study the design components of magnetic refrigeration materials and improve the magnetocaloric properties, and a method for regulating the magnetocaloric properties of magnetic refrigeration materials with a first-order phase change by controlling the length of covalent bonds.

[0006] The method of the present invention for regulating the magnetocaloric properties of a magnetic refrigeration material having a first-order phase change by controlling the length of a covalent bond comprises the following steps:

[0007] (1) The magnetocaloric material whose components need to be regulated is subjected to magnetocaloric performance test to obtain the Curie temperature (T C ) and thermal hysteresis (ΔT hys );

[0008] (2) performing X-ray diffraction (XRD) testing to obtain a series of XRD spectra;

[0009] (3) After the XRD spectrum is fitted with the Rietveld full spectrum, the lattice constants a, b, c, α, β, γ of the compound, the coordinates of each atom in the compound, and the occupancy rate are obtained; the XRD spectrum of the sample is refined for crystal structure to obtain the crystal structure parameters of each sample; the crystal structure refinement uses the full spectrum analysis software to perform Rietveld full spectrum fitting using the least squares principle, input the XRD data of the sample, and when the difference between three consecutive calculations is less than 0.001, it is determined to be convergent, and the structural parameters of the sample are output;

[0010] (4) Using crystal structure parameters to obtain the length of each covalent bond;

[0011] (5) Based on the data, mathematical induction is used to summarize the relationship between covalent bond length and Curie temperature (T C ), the difference in covalent bond length before and after phase transition and thermal hysteresis (ΔT hys ) is a proportional relationship straight line;

[0012] (6) By reversing the conclusion, we can control the magnetocaloric properties of first-order phase change magnetic refrigeration materials by controlling the length of the covalent bonds.

[0013] The present invention provides an effective method for designing material composition so that the Curie temperature (T C ) and thermal hysteresis (ΔT hys )The magnetocaloric properties can be adjusted to the optimal value. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Mn 2-x Fe x P y Ge 1-y The crystal structures of a series of compounds and the covalent bonds therein.

[0015] Figure 2 For L bond-Ⅰ Curie temperature (T C ) and thermal hysteresis (ΔT hys ) relationship.

[0016] Figure 3 For L bond-Ⅱ Curie temperature (T C ) and thermal hysteresis (ΔT hys ) relationship.

[0017] Figure 4 For L bond-Ⅲ , L bond-Ⅳ Relationship with Curie temperature (a, b) and thermal hysteresis (c, d).

[0018] Figure 5 ΔL for 6 samples bond-Ⅲ , ΔL bond-Ⅳ and thermal hysteresis. DETAILED DESCRIPTION

[0019] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solution in the embodiments will be clearly and completely described below in conjunction with the accompanying drawings. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0020] The following uses Mn 2-x Fe x P y Ge 1-y M z (M is a doping element, and there are 54 samples of different components) A series of compounds with a first-order phase transition are used as examples to further describe the present invention in detail in conjunction with the accompanying drawings:

[0021] A series of Mn 2-x Fe x P y Ge 1-y M z (M is the doping element) to obtain the Curie temperature (T C ) and thermal hysteresis (ΔT hys ).

[0022] Then perform XRD test on the sample to obtain a series of XRD spectra. After the XRD spectrum is fitted with Rietveld full spectrum, the lattice constants a, b, c, the coordinates of each atom in the compound, the occupancy rate and the temperature factor (B) are obtained. The length of each covalent bond is obtained using the structural parameters. bond-Ⅰ , L bond-Ⅱ , L bond-Ⅲ and L bond-Ⅳ Curie temperature (T C ) and thermal hysteresis (ΔT hys ) relationship.

[0023] Figure 1 Mn 2-x Fe x P y Ge 1-ySchematic diagram of the crystal structure of a series of compounds. The crystal structure has a hexagonal Fe2P type [(No.189), Z = 3], where the atomic occupancy is Mn: 3g (x, 0, 1 / 2), Fe / Mn: 3f (x, 0, 0), P / Ge (1): 1b (0, 0, 1 / 2), P / Ge (2): 2c (1 / 3, 2 / 3, 0), part of Fe is replaced by Mn, and P is replaced by Ge. Therefore, Mn 2-x Fe x P y Ge 1-y There are four kinds of tight covalent bonds in the unit cell of the series of compounds, including two interlayer covalent bonds, namely Fe / Mn-P(3f-1b) bond (named bond-Ⅰ) and Mn-P / Ge(3g-2c) bond (named bond-Ⅱ), and two coplanar covalent bonds, namely Fe / Mn-Ge / P(3f-2c) bond and Mn-P(3g-1b) bond (named bond-Ⅲ and bond-Ⅳ, respectively). The lengths of bond-Ⅰ, bond-Ⅱ, bond-Ⅲ and bond-Ⅳ are denoted as L bond-Ⅰ , L bond-Ⅱ , L bond-Ⅲ and L bond-Ⅳ .

[0024] Figure 2 and Figure 3 L bond-Ⅰ , L bond-Ⅱ The relationship between the Curie temperature and thermal hysteresis and the length of the interlayer covalent bond is shown in Figure 1. bond-Ⅰ , L bond-Ⅱ The Curie temperature and thermal hysteresis fluctuate slightly near the fitting curve and remain basically unchanged. Therefore, it can be concluded that the magnetocaloric properties are not highly correlated with the changes in the length of the interlayer covalent bonds.

[0025] Figure 4 Display L bond-Ⅲ , L bond-Ⅳ The relationship between Curie temperature and thermal hysteresis shows that T C With L bond-Ⅲ , L bond-Ⅳ Through mathematical induction, it is concluded that the covalent bond length (L bond-Ⅲ and L bond-Ⅳ ) and Curie temperature (T C ) are respectively

[0026] L bond-Ⅲ =(2.91±0.210)×10 -4 T C +2.24(±0.006)

[0027] L bond-Ⅳ =(4.41±0.317)×10 -4 T C +3.50(±0.009)

[0028] The table below shows the Curie temperature and thermal hysteresis of 6 typical undoped samples selected near the fitting curve.

[0029]

[0030] L bond-Ⅲ and L bond-Ⅳ The difference between the ferromagnetic phase and the paramagnetic phase is defined as ΔL bond-Ⅲ and ΔL bond-Ⅳ . Figure 5 = ΔL bond-Ⅲ , ΔL bond-Ⅳ and thermal hysteresis. It is noted that the covalent bond length on the ab plane of the ferromagnetic phase is significantly higher than that of the paramagnetic phase. It can be concluded that thermal hysteresis is positively correlated with the change in the covalent bond length between the ferromagnetic phase and the paramagnetic phase. By mathematical induction, it is concluded that the difference in covalent bond length (ΔL bond-Ⅲ and ΔL bond-Ⅳ ) and thermal hysteresis (ΔT hys ) are respectively

[0031] ΔL bond-Ⅲ =(5.326±1.2840)×10 -4 ΔT hys +0.026(±0.0009)

[0032] ΔL bond-Ⅳ =(9.770±1.9045)×10 -4 ΔT hys +0.068(±0.0014)

[0033] Through the "Curie temperature and L bond-Ⅲ , L bond-Ⅳ The two conclusions and corresponding expressions can be reversed, and the covalent bond length can be designed according to the required magnetocaloric properties to deduce the corresponding components.

[0034] It is understandable that the purpose of publishing this embodiment is to further help understand the present invention. However, the embodiments of the present invention are not limited thereto. Any changes and modifications are possible without departing from the scope of the present invention and the appended claims. Therefore, the scope defined by the claims of the present invention is within the scope of protection of the present invention.

Claims

1. A method for regulating the magnetocaloric properties of a first-order phase-change magnetic refrigeration material by controlling the length of a covalent bond, characterized in that: Here are the steps: Step 1: Test the magnetocaloric properties of the sample to obtain magnetocaloric performance parameters, including Curie temperature. T C and thermal hysteresis Δ T hys ; The XRD spectrum of the sample is refined for crystal structure to obtain the crystal structure parameters of each sample; the crystal structure refinement uses the full spectrum analysis software to perform Rietveld full spectrum fitting using the least squares principle, input the XRD data of the sample, and when the difference between three consecutive calculations is less than 0.001, it is judged to be converged, and the structural parameters of the sample are output; Step 2: Using crystal structure parameters to obtain the covalent bond length of the compound; the primary phase change magnetic refrigeration material is Mn 2-x Fe x P y Ge 1-y M z , and M is a doping element; Step 3, summarize the coupling relationship between the covalent bond length and the magnetocaloric properties by mathematical induction; the coupling relationship between the covalent bond length and the magnetocaloric properties is that the covalent bond length is proportional to the Curie temperature, and the difference in the covalent bond length before and after the phase change is proportional to the thermal hysteresis; Step 4: Design the compound composition by regulating the covalent bond length of the compound to improve the magnetocaloric performance.

2. The method of controlling the magnetocaloric properties of a first-order phase change magnetic refrigeration material by controlling the length of a covalent bond according to claim 1, characterized in that: In step 2, the crystal structure parameters include lattice constants a , b , c , α , β , γ and atomic occupancy.

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