Potassium europium phosphate extremely-low-temperature magnetic refrigeration material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of magnetic refrigeration materials, and particularly discloses a potassium europium phosphate extremely-low-temperature magnetic refrigeration material and a preparation method and application thereof. The material KEuPO4 belongs to an orthorhombic system, and the space group is Pnma; the polycrystalline block of the material can be prepared by adopting a step-by-step solid-phase reaction method in a hydrogen-argon mixed gas atmosphere. The magnetic phase change temperature of the material ranges from 1.0 K to 1.2 K along with the reversible giant magnetocaloric effect, under the magnetic field changes of 0-2 T and 0-5 T, the maximum isothermal magnetic entropy change values of the material range from 32.8 J / kg.K to 33.4 J / kg.K and 49.7 J / kg.K to 52.1 J / kg.K respectively, and the maximum isothermal magnetic entropy change values of the material are both superior to those of a commercial extremely-low-temperature magnetic refrigeration material Gd3Ga5O12. The europium-based phosphate KEuPO4 material provided by the invention has the advantages of simple preparation process, good material stability, remarkable magnetocaloric effect and the like, and has a relatively good application prospect in the field of extremely low-temperature magnetic refrigeration.

Description

Technical Field

[0001] This invention relates to the field of rare earth magnetic functional materials technology, and in particular to a potassium europium phosphate ultra-low temperature magnetic refrigeration material, its preparation method and application. Background Technology

[0002] High-performance cryogenic refrigeration technology has broad application prospects and plays an irreplaceable role in scientific and technological fields such as quantum computing, space exploration, high-energy physics, low-temperature superconductivity, and nuclear technology. These fields generally require cold source equipment to have low vibration, low noise, high stability, and long operating cycles. Magnetic refrigeration technology is a novel solid-state refrigeration method that utilizes the magnetocaloric effect of materials to achieve refrigeration. Compared with traditional gas compression / expansion refrigeration technology, magnetic refrigeration has advantages such as compact structure, fewer moving parts, long lifespan, less leakage, no dependence on gravity, and potential high efficiency, which can fully meet the above requirements.

[0003] Magnetocaloric effect is a physical phenomenon characterized by heat absorption / release during the change in magnetic moment order of a material system due to a change in an applied magnetic field. The magnitude of the magnetocaloric effect is crucial in determining the material's cooling capacity and efficiency. Current research on ultra-low temperature magnetic refrigeration materials mainly focuses on hydrated paramagnetic salts such as FeNH4(SO4)2·12H2O (ferric ammonium sulfate, FAA), Mn(NH4)2(SO4)2·6H2O (manganese ammonium sulfate, MAS), KCr(SO4)2·12H2O (potassium chromium sulfate, CPA), and rare-earth gallium garnet Gd3Ga5O4. 12 (GGG) single crystals or powders are commercially available. However, these magnetic refrigeration materials generally have relatively small magnetic entropy changes under low magnetic field variations, and there are certain limitations in their use, such as slow thermal diffusion of paramagnetic hydrate salts, easy dehydration by water molecules, poor crystal stability, and relatively complex preparation processes.

[0004] Existing technologies, such as "A New Type of Divalent Europium Compound MEuPO, (M = K, Rb, Cs), its Synthesis, Crystal Structure, and Properties," disclose a method for preparing potassium europium phosphate. This method involves first preparing a EuPO4 precursor by reacting Eu(NO3)3 or Eu2O3 with phosphate, and then using potassium alkali metal as a reducing agent. This method requires a sealed environment, and the entire preparation cycle takes several days. The reaction is slow, making mass production difficult, and it is unsuitable for magnetic refrigeration materials, as these materials require high yields to achieve a cooling effect and be applicable to magnetic refrigeration. Summary of the Invention

[0005] To address the aforementioned problems and shortcomings, this invention provides a potassium europium phosphate ultra-low temperature magnetic refrigeration material and its preparation method. The material, with the chemical formula KEuPO4 polycrystalline bulk, possesses advantages such as simple preparation process, good material stability, and significant magnetocaloric effect, making it suitable for ultra-low temperature magnetic refrigeration. The purpose of this invention is to solve the problems of low magnetic entropy, complex preparation process, long preparation cycle, and poor stability in existing ultra-low temperature magnetic refrigeration materials.

[0006] The potassium europium phosphate ultra-low temperature magnetic refrigeration material provided by this invention has the molecular formula KEuPO4, is composed of a single phase, belongs to the orthorhombic crystal system, and has a space group of Pnma lattice constant a =7.3590(2)Å、 b =5.5690(6)Å、 c =9.6300(4)Å; α = β = γ =90 o The present invention also provides a method for preparing the potassium europium phosphate ultra-low temperature magnetic refrigeration material, which can be obtained by a stepwise solid-state reaction method in a hydrogen-argon mixed gas atmosphere; at the same time, the application of the potassium europium phosphate in ultra-low temperature magnetic refrigeration is disclosed, with a magnetic phase transition temperature of 1.0-1.2 K, and the maximum isothermal magnetic entropy change values ​​of 32.8-33.4 J / kg·K and 49.7-52.1 J / kg·K under an applied magnetic field of 0-2T and 0-5T, respectively.

[0007] Specifically, this invention provides a method for preparing a potassium europium phosphate ultra-low temperature magnetic refrigeration material, comprising the following steps: (1) Obtain europium source, K2CO3 and NH4H2PO4 as raw materials; the europium source is Eu2O3 or Eu(NO3)3; (2) Weigh the raw materials according to the molar ratio of Eu:K:P elements of 1:1:1.1 to 1:1:1.2, grind them thoroughly, mix them evenly, and pre-calcine them at 500-570℃ for 3-5 hours; (3) After the pre-calcined powder is fully ground and pressed into tablets, a second sintering is carried out at 950-1050℃ for 7-10 hours. After the second sintering is completed, the precursor is cooled to room temperature in the furnace. (4) After crushing the precursor obtained in step (3), add 1 to 1.25 times the amount of K2CO3 used in step (2), grind thoroughly again, mix evenly, compress into tablets, sinter at 1200-1320℃ for 12-18 hours, and then cool to room temperature in the furnace to obtain KEuPO4 polycrystalline bulk material; the KEuPO4 polycrystalline bulk material, as potassium europium phosphate ultra-low temperature magnetic refrigeration material, is composed of a single phase, belongs to the orthorhombic crystal system, has a space group of Pnma, and a lattice constant of a =7.3590(2)Å、b =5.5690(6)Å、 c =9.6300(4)Å; α = β = γ =90 o .

[0008] Preferably, in steps (3) and (4), the pressure applied during tablet compression is 500-800 MPa, and the pressure holding time is 3-8 minutes.

[0009] Preferably, the pre-firing in step (2), the sintering in step (3) and step (4) are all carried out in a flowing mixed atmosphere containing hydrogen and argon.

[0010] Preferably, the heating rate in step (2) preheating, step (3) and step (4) sintering is 3-5℃ / min.

[0011] Preferably, the volume fraction of hydrogen in the mixed atmosphere is 5-10%.

[0012] Preferably, the purity of Eu2O3, Eu(No3)3, NH4H2PO4 and K2CO3 is not less than 99.9%.

[0013] The present invention also provides a potassium europium phosphate low-temperature magnetic refrigeration material prepared by the preparation method described above.

[0014] The present invention also provides the application of the potassium europium phosphate cryogenic magnetic refrigeration material, which performs cryogenic magnetic refrigeration at an ambient temperature of 1.0-1.2 K and an applied magnetic field of 0-2T and 0-5T. The isothermal magnetic entropy change of the potassium europium phosphate cryogenic magnetic refrigeration material reaches 32.8-33.4 J / kg·K and 49.7-52.1 J / kg·K, respectively.

[0015] The present invention has the following beneficial effects: 1. The potassium europium phosphate ultra-low temperature magnetic refrigeration material KEuPO4 prepared in this invention has a magnetic phase transition temperature of 1.0-1.2K. Under applied magnetic fields of 0-2T and 0-5T, the maximum isothermal magnetic entropy change is 32.8-33.4 J / kg·K and 49.7-52.1 J / kg·K, respectively, both of which are superior to the commercially available ultra-low temperature magnetic refrigeration material Gd3Ga5O. 12 (14.6 J / kg·K and 32.8 J / kg·K).

[0016] 2. The potassium europium phosphate ultra-low temperature magnetic refrigeration material KEuPO4 described in this invention can be prepared by a stepwise solid-phase reaction method, which has the advantages of simple preparation process, short preparation cycle and good structural stability, and has excellent application prospects in the field of low temperature magnetic refrigeration.

[0017] 3. This invention relates to rare earth magnetic functional materials, which can simultaneously promote the high-value-added utilization of rare earth resources and enhance the international competitiveness and technological strength of my country's rare earth industry.

[0018] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0019] Figure 1 X-ray powder diffraction pattern of potassium europium phosphate ultra-low temperature magnetic refrigeration material KEuPO4 prepared in Example 1 of this invention; Figure 2 The crystal structure diagram of potassium europium phosphate ultra-low temperature magnetic refrigeration material KEuPO4 prepared in Example 1 of the present invention is shown. Figure 3 The X-ray photoelectron spectrum of potassium europium phosphate ultra-low temperature magnetic refrigeration material KEuPO4 prepared in Example 1 of this invention; Figure 4 Transmission electron micrograph of potassium europium phosphate ultra-low temperature magnetic refrigeration material KEuPO4 prepared in Example 1 of this invention; Figure 5 The graph shows the magnetization intensity as a function of temperature for the potassium europium phosphate ultra-low temperature magnetic refrigeration material KEuPO4 prepared in Example 1 of this invention under magnetic field cooling and zero field cooling tests at 0.1T. Figure 6 The isothermal magnetic entropy change curve of potassium europium phosphate ultra-low temperature magnetic refrigeration material KEuPO4 prepared in Example 1 of the present invention as a function of temperature under different magnetic field strengths; Figure 7 The graph shows the magnetization intensity of the potassium europium phosphate low-temperature magnetic refrigeration material KEuPO4 prepared in Example 1 of the present invention as a function of magnetic field at different temperatures. Detailed Implementation

[0020] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0021] Example 1 KEuPO4 material was prepared and tested using a stepwise solid-state method, including the following steps: (1) Weigh 0.1 mol of Eu2O3, 0.1 mol of K2CO3 and 0.22 mol of NH4H2PO4 respectively, grind them thoroughly, mix them evenly, and pre-calcine them at 520°C for 5 hours in a 5% hydrogen-argon mixed gas. (2) The pre-calcined powder is fully ground and pressed into tablets, sintered at 1000°C for 8 hours in a 5% hydrogen-argon mixed gas, and then cooled to room temperature in the furnace to obtain the precursor. (3) After crushing the precursor obtained in the previous step, add 0.1 mol of K2CO3 and grind it thoroughly again. Mix it evenly, press it into tablets, and sinter it at 1250°C for 16 hours in a 5% hydrogen-argon mixed gas. Then cool it to room temperature in the furnace to obtain KEuPO4 polycrystalline bulk.

[0022] The crystal structure of the KEuPO4 material obtained in this embodiment was characterized by X-ray powder diffraction, and the results are as follows: Figure 1 As shown, the measured sample exhibits excellent single-phase properties, and after refinement, it was found to belong to the orthorhombic crystal system with a space group of [missing information]. Pnma lattice constant a =7.3590(2)Å、 b =5.5690(6)Å、 c =9.6300(4)Å; α = β = γ =90 o Its crystal structure diagram is as follows: Figure 2 As shown.

[0023] The chemical valence state of the KEuPO4 material obtained in this embodiment was characterized using X-ray photoelectron spectroscopy, and the results are as follows: Figure 3 As shown, it can be seen that in the sample measured, K has a +1 valence, Eu has a +2 valence, P has a +5 valence, and O has a -2 valence.

[0024] The microstructure and microstructure of the KEuPO4 material obtained in this embodiment were characterized using transmission electron microscopy, and the results are as follows: Figure 4 As shown, the low-magnification (a) and high-magnification (b) micrographs and the electron diffraction (c) pattern indicate that the measured sample has typical single-phase polycrystalline characteristics. The surface scanning elemental energy dispersive X-ray spectrum (dh) shows that all constituent elements are uniformly distributed, which is consistent with the X-ray powder diffraction results.

[0025] The magnetization of the KEuPO4 material obtained in this embodiment under different temperatures and magnetic fields was measured using a vibrating sample magnetometer manufactured by Quantum Design, Inc., USA. The results are as follows: Figure 5 and 6 As shown, it can be observed that the measured sample undergoes a magnetic phase transition from antiferromagnetic to ferromagnetic near 1.1K, and exhibits strong magnetism at extremely low temperatures.

[0026] The isothermal magnetic entropy change of the KEuPO4 material under different magnetic field variations was calculated based on Maxwell's relation, and the results are as follows: Figure 7 As shown, the isothermal magnetic entropy changes at 0-2T and 0-5T can reach 33.1 J / kg·K and 50.1 J / kg·K, respectively, both of which are superior to those of commercial Gd3Ga5O. 12(14.6 J / kg·K and 32.8 J / kg·K), indicating that the KEuPO4 material obtained in this embodiment has good application potential in the field of ultra-low temperature magnetic refrigeration.

[0027] Example 2 KEuPO4 material was prepared and tested using a stepwise solid-state method, including the following steps: (1) Weigh 0.2 mol of Eu2O3, 0.2 mol of K2CO3 and 0.46 mol of NH4H2PO4 respectively, grind them thoroughly, mix them evenly, and pre-calcine them at 560°C for 3 hours in an 8% hydrogen-argon mixed gas. (2) The pre-calcined powder is fully ground and pressed into tablets, sintered at 1020°C for 8 hours in an 8% hydrogen-argon mixed gas, and then cooled to room temperature in the furnace to obtain the precursor. (3) After crushing the precursor obtained in the previous step, add 0.25 mol of K2CO3 and grind it thoroughly again. Mix it evenly, press it into tablets, and sinter it at 1300℃ for 16 hours in an 8% hydrogen-argon mixed gas. Then cool it to room temperature in the furnace to obtain KEuPO4 polycrystalline bulk.

[0028] The crystal structure of the KEuPO4 material obtained in this embodiment was characterized by X-ray powder diffraction, which showed that the sample had good single-phase properties. The magnetization of the KEuPO4 material obtained in this embodiment under different temperatures and magnetic fields was measured using a vibrating sample magnetometer. It was found that the sample underwent an antiferromagnetic to ferromagnetic magnetic phase transition near 1.0 K. According to Maxwell's relation, the isothermal magnetic entropy change of the KEuPO4 material obtained in this embodiment at 0-2T and 0-5T can reach 33.4 J / kg·K and 52.1 J / kg·K, respectively, indicating that the KEuPO4 material obtained in this embodiment has good application potential in the field of ultra-low temperature magnetic refrigeration.

[0029] Example 3 KEuPO4 material was prepared and tested using a stepwise solid-state method, including the following steps: (1) Weigh 0.1 mol of Eu(No3)3, 0.05 mol of K2CO3 and 0.12 mol of NH4H2PO4 respectively, grind them thoroughly, mix them evenly, and pre-calcine them at 550°C for 3 hours in a 5% hydrogen-argon mixed gas. (2) The pre-calcined powder is fully ground and pressed into tablets, sintered at 980°C for 10 hours in a 10% hydrogen-argon mixed gas, and then cooled to room temperature in the furnace to obtain the precursor. (3) After crushing the precursor obtained in the previous step, add 0.06 mol of K2CO3 and grind it thoroughly again. Mix it evenly, press it into tablets, and sinter it at 1200℃ for 12 hours in a 5% hydrogen-argon mixed gas. Then cool it to room temperature in the furnace to obtain KEuPO4 polycrystalline bulk.

[0030] The crystal structure of the KEuPO4 material obtained in this embodiment was characterized by X-ray powder diffraction. It can be seen that the measured sample has good single-phase properties. The magnetization of the KEuPO4 material obtained in this embodiment under different temperatures and magnetic fields was measured using a vibrating sample magnetometer. It was found that the magnetic phase transition of the measured sample is 1.2K. At 0-2T and 0-5T, its isothermal magnetic entropy change can reach 32.8 J / kg·K and 49.7 J / kg·K, respectively. This indicates that the KEuPO4 material obtained in this embodiment has good application potential in the field of ultra-low temperature magnetic refrigeration.

[0031] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a potassium europium phosphate ultra-low temperature magnetic refrigeration material, characterized in that, Includes the following steps: (1) Obtain europium source, K2CO3 and NH4H2PO4 as raw materials; the europium source is Eu2O3 or Eu(NO3)3; (2) Weigh the raw materials according to the molar ratio of Eu:K:P elements of 1:1:1.1 to 1:1:1.2, grind them thoroughly, mix them evenly, and pre-calcine them at 500-570℃ for 3-5 hours; (3) After the pre-calcined powder is fully ground and pressed into tablets, a second sintering is carried out at 950-1050℃ for 7-10 hours. After the second sintering is completed, the precursor is cooled to room temperature in the furnace. (4) After crushing the precursor obtained in step (3), add 1 to 1.25 times the amount of K2CO3 used in step (2), grind thoroughly again, mix evenly, compress into tablets, sinter at 1200-1320℃ for 12-18 hours, and then cool to room temperature in the furnace to obtain KEuPO4 polycrystalline bulk material; the KEuPO4 polycrystalline bulk material, as potassium europium phosphate ultra-low temperature magnetic refrigeration material, is composed of a single phase, belongs to the orthorhombic crystal system, has a space group of Pnma, and a lattice constant of a =7.3590(2)Å、 b =5.5690(6)Å、 c =9.6300(4)Å; α = β = γ =90 o .

2. The preparation method according to claim 1, characterized in that, In steps (3) and (4), the pressure applied during tablet compression is 500-800 MPa, and the pressure holding time is 3-8 minutes.

3. The preparation method according to claim 1, characterized in that, The pre-firing in step (2), and the sintering in steps (3) and (4) are all carried out in a flowing mixed atmosphere containing hydrogen and argon.

4. The preparation method according to claim 1, characterized in that, The heating rate in step (2) pre-firing, step (3) and step (4) sintering is 3-5℃ / min.

5. The preparation method according to claim 3, characterized in that, The volume fraction of hydrogen in the mixed atmosphere is 5-10%.

6. The preparation method according to claim 1, characterized in that: The purity of Eu2O3, Eu(NO3)3, NH4H2PO4 and K2CO3 is not less than 99.9%.

7. A potassium europium phosphate low-temperature magnetic refrigeration material prepared using the preparation method according to any one of claims 1 to 6.

8. The application of the potassium europium phosphate ultra-low temperature magnetic refrigeration material according to claim 7, characterized in that: Low-temperature magnetic refrigeration was performed at an ambient temperature of 1.0-1.2K and an applied magnetic field of 0-2T and 0-5T, respectively. The isothermal magnetic entropy change of the potassium europium phosphate ultra-low temperature magnetic refrigeration material reached 32.8-33.4J / kg·K and 49.7-52.1J / kg·K, respectively.

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