Gadolinium-based molybdate magnetic refrigeration material and preparation method and application thereof

Abstract

The invention belongs to the field of magnetic refrigeration materials, and particularly discloses a gadolinium-based molybdate magnetic refrigeration material and a preparation method and application thereof. The gadolinium-based molybdate magnetic refrigeration material comprises GdXMoO4, wherein X is F, Cl, Br or I; the magnetic phase change temperature of the gadolinium-based molybdate magnetic refrigeration material is less than 2K, and the maximum magnetic entropy change of the gadolinium-based molybdate magnetic refrigeration material is greater than or equal to 12J. Kg <-1 >. K <-1 > when the magnetic field change is 0-50kOe. The gadolinium-based molybdate magnetic refrigeration material disclosed by the invention has extremely low magnetic phase transition temperature, has relatively high magnetocaloric efficiency in a low magnetic field, is an extremely low temperature region magnetic refrigeration material with excellent performance, and has a wide application prospect in the field of extremely low temperature magnetic refrigeration.

Description

Technical Field

[0001] The invention belongs to the field of magnetic refrigeration materials, and specifically relates to a gadolinium-based molybdate magnetic refrigeration material and a preparation method and application thereof. Background Art

[0002] Ultra-low temperature refrigeration technology is a major national need and one of the key supporting technologies for cutting-edge science. Low temperature refrigeration technology has brought about amazing discoveries such as superconductivity and superfluids, driving scientists to explore unknown things at lower temperatures. Ultra-low temperature refrigeration technology is usually used in aerospace and space exploration, condensed matter physics, and quantum computers. The increasing demand for refrigeration technology in the scientific field is also driving new changes in refrigeration technology. Traditional ultra-low temperature zone refrigeration methods include: 3 He adsorption refrigeration and 3 He- 4 He dilution refrigeration technology. Usually dilution refrigeration can achieve lower temperatures, but it requires 3 He, 4 He is stably placed in different cabins and relies on gravity for operation. When applied in the aerospace field, it is limited. Both adsorption refrigeration and dilution refrigeration rely on scarce resources. 3 He. 3 He mainly comes from the byproduct of tritium radioactive decay produced in nuclear reactors or nuclear weapons stockpiles. The reserves on Earth are very scarce, so it is necessary to find a source that does not rely on 3 New refrigeration technology for He resources.

[0003] Solid-state phase change materials will rapidly respond thermally (isothermal entropy change and adiabatic temperature change) when driven by external fields such as magnetic field, electric field, uniaxial pressure and net water pressure (pressure), which is the solid-state phase change thermal effect. This effect can absorb and release heat from the surrounding environment, and a cooling effect can be produced by the endothermic process. This type of material has very little impact on the environment, so the solid-state phase change thermal effect provides a theoretical basis for the research and development of a new generation of green refrigeration technology. Magnetic refrigeration technology is a new solid-state refrigeration technology based on the magnetocaloric effect (MCE) of magnetic materials, that is, the physical phenomenon that magnetic materials release heat when the magnetic field is enhanced and absorb heat when the magnetic field is weakened. The essence is the change in the order of the magnetic moment (that is, magnetic entropy change). Adiabatic demagnetization refrigeration (ADR) technology does not rely on 3 It is a more feasible alternative because it is resource-efficient, energy-efficient and highly efficient.

[0004] High-performance magnetocaloric materials play a key role in magnetic refrigeration technology, especially refrigerants with large magnetocaloric effect (MCE) under low external magnetic field (≤20000kOe) are very desirable because they can simplify the design by using permanent magnets and greatly reduce the cost of magnetic refrigerators. Therefore, materials with large magnetocaloric effect under low magnetic field have more application prospects. However, in the field of magnetic refrigeration materials, the existing methods are not only unable to obtain magnetic refrigeration materials with large magnetocaloric effect under low external magnetic field (especially ≤50kOe), but also usually have defects such as environmental pollution, difficulty in large-scale production, high energy consumption, long preparation cycle, and easy deterioration, which cannot meet the needs of practical applications.

[0005] Therefore, it is necessary to develop ultra-low temperature magnetic refrigeration materials with large magnetic entropy change under lower magnetic fields, simple preparation process, short cycle, and suitable for industrial production. Summary of the invention

[0006] In view of the defects of the magnetic refrigeration materials involved in the above-mentioned prior art, such as the lack of magnetocaloric effect under low external magnetic field and the existence of defects in the preparation process, such as environmental pollution, difficulty in large-scale production, high energy consumption, long preparation cycle, and easy deterioration, the present invention will provide a gadolinium-based molybdate magnetic refrigeration material and its preparation method and application.

[0007] To achieve the above purpose, the following technical solutions are specifically included:

[0008] In a first aspect, the present invention provides a gadolinium-based molybdate magnetic refrigeration material, including GdXMoO4, X is F, Cl, Br or I; the magnetic phase transition temperature of the gadolinium-based molybdate magnetic refrigeration material is less than 2K, and the maximum magnetic entropy change of the gadolinium-based molybdate magnetic refrigeration material is ≥12J·kg under a magnetic field change of 0-50kOe. -1 ·K -1 .

[0009] The gadolinium-based molybdate magnetic refrigeration material of the present invention has a magnetic phase transition temperature in an extremely low temperature region and has a high magnetocaloric effect under a low magnetic field, and is an extremely low temperature magnetic refrigeration material with excellent performance.

[0010] The magnetic phase transition temperature in the present invention refers to the temperature at which a material changes from a paramagnetic state to an antiferromagnetic state.

[0011] The present invention can use Maxwell's relation to calculate the magnetic entropy change under different magnetic field strength changes according to the isothermal magnetization curve of the gadolinium-based molybdate magnetic refrigeration material, and can obtain the maximum magnetic entropy change under the change of the magnetic field strength. And the maximum magnetic entropy change of the gadolinium-based molybdate magnetic refrigeration material of the present invention is obtained at a temperature near 1.3K.

[0012] As a preferred embodiment of the present invention, X is F or Cl.

[0013] As a preferred embodiment of the present invention, the magnetic phase transition temperature of the gadolinium-based molybdate magnetic refrigeration material is 0.4K to 1.8K, and more preferably 1.1-1.4K. For example, it can be 0.4K, 0.6K, 0.8K, 1K, 1.2K, 1.4K, 1.6K, 1.8K, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0014] As a preferred embodiment of the present invention, when the magnetic field changes from 0 to 10 kOe, the maximum magnetic entropy change of the gadolinium-based molybdate magnetic refrigeration material is ≥13 J·kg -1 ·K -1 .

[0015] As a further preferred embodiment of the present invention, when the magnetic field changes from 0 to 10 kOe, the maximum magnetic entropy change of the gadolinium-based molybdate magnetic refrigeration material is 13.5 J·kg -1 ·K -1 Up to 20 J·kg -1 ·K -1 , for example, it can be 13.5 J·kg -1 ·K -1 , 14.5 J·kg -1 ·K -1 , 15.5 J·kg -1 ·K -1 , 16.5 J·kg -1 ·K -1 , 17.5 J·kg -1 ·K -1 , 18.5 J·kg -1 ·K -1 、19.5J·kg -1 ·K -1 , 20J·kg -1 ·K -1 , but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0016] As a preferred embodiment of the present invention, when the magnetic field changes from 0 to 20 kOe, the maximum magnetic entropy change of the gadolinium-based molybdate magnetic refrigeration material is ≥30 J·kg -1 ·K -1 .

[0017] As a further preferred embodiment of the present invention, when the magnetic field changes from 0 to 20 kOe, the maximum magnetic entropy change of the gadolinium-based molybdate magnetic refrigeration material is 30 J·kg -1 ·K -1 Up to 40 J·kg -1 ·K -1 , for example, it can be 30 J·kg-1 ·K -1 、31.5J·kg -1 ·K -1 、32.5J·kg -1 ·K -1 、33.5J·kg -1 ·K -1 、34.5J·kg -1 ·K -1 、35.5J·kg -1 ·K -1 、36.5J·kg -1 ·K -1 、37.5J·kg -1 ·K -1 、38.5J·kg -1 ·K -1 、39.5J·kg -1 ·K -1 , 40J·kg -1 ·K -1 , but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0018] As a preferred embodiment of the present invention, when the magnetic field changes from 0 to 30 kOe, the maximum magnetic entropy change of the gadolinium-based molybdate magnetic refrigeration material is ≥32 J·kg -1 ·K -1 ; More preferably 35J·kg -1 ·K -1 Up to 40 J·kg -1 ·K -1 , for example, it can be 35 J·kg -1 ·K -1 、36J·kg -1 ·K -1 、37J·kg -1 ·K -1 、38J·kg -1 ·K -1 、39J·kg -1 ·K -1 , 40J·kg -1 ·K -1 , but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0019] As a preferred embodiment of the present invention, when the magnetic field changes from 0 to 40 kOe, the maximum magnetic entropy change of the gadolinium-based molybdate magnetic refrigeration material is ≥39 J·kg -1 ·K -1 ; More preferably 40J·kg -1 ·K-1 Up to 45 J·kg -1 ·K -1 , for example, it can be 40 J·kg -1 ·K -1 , 41J·kg -1 ·K -1 , 42J·kg -1 ·K -1 、43J·kg -1 ·K -1 , 44J·kg -1 ·K -1 、45J·kg -1 ·K -1 , but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0020] As a preferred embodiment of the present invention, when the magnetic field changes from 0 to 50 kOe, the maximum magnetic entropy change of the gadolinium-based molybdate magnetic refrigeration material is 12.5 J·kg -1 ·K -1 Up to 50J·kg -1 ·K -1 , and more preferably 45 J·kg -1 ·K -1 Up to 49 J·kg -1 ·K -1 , for example, it can be 12.5 J·kg -1 ·K -1 , 15J·kg -1 ·K -1 , 20J·kg -1 ·K -1 , 25J·kg -1 ·K -1 、30J·kg -1 ·K -1 、35J·kg -1 ·K -1 , 40J·kg -1 ·K -1 , 45J·kg -1 ·K -1 , 50J·kg -1 ·K -1 , but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0021] As a preferred embodiment of the present invention, the gadolinium-based molybdate magnetic refrigeration material includes GdFMoO4, and the maximum magnetic entropy change of the GdFMoO4 is ≥14 J·kg under a magnetic field change of 0-50 kOe. -1 ·K -1 .

[0022] As a preferred embodiment of the present invention, the gadolinium-based molybdate magnetic refrigeration material includes GdClMoO4, and the maximum magnetic entropy change of the GdClMoO4 is ≥17 J·kg under a magnetic field change of 0-50 kOe. -1 ·K -1 .

[0023] As a preferred embodiment of the present invention, the gadolinium-based molybdate magnetic refrigeration material includes GdFMoO4, and the unit cell information of the GdFMoO4 is as follows: α=γ=90°, β=106°, belongs to the monoclinic crystal system, and the space group is P21 / c.

[0024] As a preferred embodiment of the present invention, the gadolinium-based molybdate magnetic refrigeration material includes GdClMoO4, and the unit cell information of the GdClMoO4 is as follows: α=γ=90°, β=112°, it belongs to the monoclinic crystal system and its space group is C2 / m.

[0025] In a second aspect, the present invention provides a method for preparing the gadolinium-based molybdate magnetic refrigeration material, comprising the following steps:

[0026] S1, mixing Gd2O3, GdX3, MoO3 and a solvent, and sequentially ball milling and drying to obtain a mixture;

[0027] S2, performing a first tableting and a first sintering on the mixed material in sequence to obtain a precursor;

[0028] S3, grinding, tableting and sintering the precursor in sequence to obtain the gadolinium-based molybdate magnetic refrigeration material.

[0029] In the method of the present invention, the raw materials are first mixed by ball milling to make them more evenly mixed, and then tableting is performed to increase the contact area between the reaction raw materials and reduce the volatilization of the raw materials; then the first sintering is performed to form a precursor; and grinding and tableting are continued to increase the uniformity and contact area between the substances again, thereby improving the activity of the solid phase reaction and facilitating the improvement of the purity of the product.

[0030] As a preferred embodiment of the present invention, in step S1, the GdX3 includes GdF3.

[0031] As a preferred embodiment of the present invention, in step S1, the molar ratio of Gd2O3, GdX3 and MoO3 is Gd2O3:GdX3:MoO3=1:(0.9-1.1):(2-4).

[0032] As a preferred embodiment of the present invention, in step S1, the ball milling time is 5-8 hours.

[0033] As a preferred embodiment of the present invention, in step S1, the solvent includes ethanol.

[0034] As a preferred embodiment of the present invention, in step S1, the mass ratio of the total mass of Gd2O3, GdX3, and MoO3 to the mass ratio of the solvent is 1:(1-4).

[0035] As a preferred embodiment of the present invention, in step S2, the temperature of the first sintering is 600-700°C, for example, it can be 600°C, 610°C, 620°C, 630°C, 640°C, 650°C, 660°C, 670°C, 680°C, 690°C, 700°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0036] As a preferred embodiment of the present invention, in step S2, the first sintering time is 4-8h, for example, it can be 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0037] As a preferred embodiment of the present invention, in step S3, the temperature of the second sintering is 800-1000°C, for example, it can be 800°C, 825°C, 850°C, 875°C, 900°C, 925°C, 950°C, 975°C, 1000°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0038] As a preferred embodiment of the present invention, in step S3, the time of the second sintering is 3-9h, for example, it can be 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0039] In a third aspect, the present invention provides another method for preparing the gadolinium-based molybdate magnetic refrigeration material, comprising the following steps:

[0040] S1, sintering GdX3·nH2O for the first time to obtain GdOX, wherein n in GdX3·nH2O represents that GdX3 contains n molecules of crystal water, and n is 1 to 6;

[0041] S2, sintering the GdOX and MoO3 for a second time in an inert gas atmosphere to obtain the gadolinium-based molybdate magnetic refrigeration material.

[0042] As a preferred embodiment of the present invention, in step S1, the GdX3·nH2O includes GdF3·6H2O.

[0043] As a preferred embodiment of the present invention, in step S1, the temperature of the first sintering is 400-600°C, for example, it can be 400°C, 425°C, 450°C, 475°C, 500°C, 525°C, 550°C, 575°C, 600°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0044] As a preferred embodiment of the present invention, in step S1, the first sintering time is 3-6h, for example, it can be 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0045] As a preferred embodiment of the present invention, in step S2, the temperature of the second sintering is 800-1000°C, for example, it can be 800°C, 825°C, 850°C, 875°C, 900°C, 925°C, 950°C, 975°C, 1000°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0046] As a preferred embodiment of the present invention, in step S2, the time for the second sintering is 10-20 hours, for example, it can be 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0047] As a preferred embodiment of the present invention, in step S2, the second sintering is in a sealed environment.

[0048] As a preferred embodiment of the present invention, in step S2, the molar ratio of GdOX to MoO3 is 1:(0.9-1.1).

[0049] As a preferred embodiment of the present invention, in step S2, the inert gas atmosphere includes at least one of nitrogen, helium and argon.

[0050] The present invention provides two solid-phase reaction methods for preparing gadolinium-based molybdate magnetic refrigeration materials, both of which can efficiently, in a short period of time and with relatively low energy consumption, prepare gadolinium-based molybdate magnetic refrigeration materials with high magnetocaloric effect, stable performance and not easy to deteriorate under a low external magnetic field, and are suitable for industrial applications.

[0051] In a fourth aspect, the present invention provides an application of the gadolinium-based molybdate magnetic refrigeration material in the preparation of a magnetic refrigeration device.

[0052] The gadolinium-based molybdate magnetic refrigeration material of the present invention has a high magnetocaloric effect in an extremely low temperature region and under a low external magnetic field, and is very suitable for use in the preparation of devices in the fields of condensed matter physics, dark matter search, quantum information science, and space exploration magnetic refrigeration technology.

[0053] Compared with the prior art, the present invention has the following beneficial effects:

[0054] (1) The gadolinium-based molybdate magnetic refrigeration material provided by the present invention has an extremely low magnetic phase transition temperature and a high magnetocaloric effect under low magnetic fields. In particular, when the magnetic field changes from 0 to 50 kOe, the maximum magnetic entropy change of the gadolinium-based molybdate magnetic refrigeration material is ≥12 J·kg -1 ·K -1 , is a magnetic refrigeration material with superior performance in the ultra-low temperature range.

[0055] (2) The preparation method of the gadolinium-based molybdate magnetic refrigeration material provided by the present invention is a solid-phase reaction method, which has a simple preparation process, a short preparation cycle, low energy consumption, and is suitable for large-scale industrial production. In addition, no acid or alkali or other substances that seriously pollute the environment are required during the preparation process, and the green environmental protection advantage is significant. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 This is a crystal structure diagram of the gadolinium-based molybdate magnetic refrigeration material GdFMoO4 of the present invention.

[0057] Figure 2 This is a comparison chart of the X-ray diffraction spectrum of GdFMoO4 prepared in Examples 1-4 of the present invention and the theoretical spectrum.

[0058] Figure 3 It is a comparison diagram of the X-ray diffraction patterns of the materials obtained in Example 1 of the present invention and Comparative Examples 1-2 and the theoretical spectrum of GdFMoO4.

[0059] Figure 4 Field cooling (FC) thermomagnetic curve of GdFMoO4 prepared in Example 1 of the present invention under a magnetic field of 500Oe.

[0060] Figure 5 This is the isothermal magnetization curve of GdFMoO4 prepared in Example 1 of the present invention at 0.4K-1.8K under a magnetic field variation of 0-50kOe.

[0061] Figure 6 This is the relationship between the magnetic entropy change and temperature of GdFMoO4 prepared in Example 5 of the present invention under different magnetic field changes.

[0062] Figure 7 This is a crystal structure diagram of the gadolinium-based molybdate magnetic refrigeration material GdClMoO4 of the present invention.

[0063] Figure 8 This is a comparison chart of the X-ray diffraction spectrum of GdClMoO4 prepared in Examples 5-8 of the present invention and the theoretical spectrum.

[0064] Fig. 9 It is a comparison chart of the X-ray diffraction patterns of the materials prepared in Example 5 of the present invention and Comparative Examples 3-4 and the theoretical spectrum of GdClMoO4.

[0065] Fig.10 This is the field cooling (FC) thermomagnetic curve of GdClMoO4 prepared in Example 5 of the present invention under a magnetic field of 500Oe.

[0066] Fig.11 This is the isothermal magnetization curve of GdClMoO4 prepared in Example 5 of the present invention at 0.4K-1.8K under a magnetic field variation of 0-50kOe.

[0067] Fig.12 This is the relationship between the magnetic entropy change and temperature of GdClMoO4 prepared in Example 5 of the present invention under different magnetic field changes. DETAILED DESCRIPTION

[0068] In order to better illustrate the purpose, technical scheme and advantages of the present invention, the present invention will be further described below through specific examples. The test methods used in the examples and / or comparative examples are conventional methods unless otherwise specified; the materials, reagents, etc. used can be obtained from commercial channels unless otherwise specified.

[0069] Example 1

[0070] A method for preparing a gadolinium-based molybdate magnetic refrigeration material comprises the following steps:

[0071] S1. Preparation of mixed material: Gd2O3, GdF3 and MoO3 were mixed in a molar ratio of 1:1:3, and then an appropriate amount of anhydrous ethanol was added, followed by ball milling for 6 hours and drying to obtain a mixed material;

[0072] S2, pre-sintering: the mixed material obtained in step S1 is pressed into a sheet for the first time, placed in a tube furnace, and sintered for the first time at 600° C. in an argon atmosphere for 6 hours to obtain a precursor;

[0073] S3. Grind the precursor obtained in step S2, perform a second tabletting, place it in a tube furnace, and perform a second sintering for 6 hours at 850° C. in an argon atmosphere to obtain a GdFMoO4 magnetic refrigeration material.

[0074] Example 2

[0075] A method for preparing a gadolinium-based molybdate magnetic refrigeration material comprises the following steps:

[0076] S1. Preparation of mixed material: Gd2O3, GdF3 and MoO3 were mixed, and an appropriate amount of anhydrous ethanol was added, followed by ball milling for 6 hours and drying to obtain a mixed material;

[0077] S2, pre-sintering: the mixed material obtained in step S1 is pressed into a sheet for the first time, placed in a tube furnace, and sintered for the first time at 600° C. in an argon atmosphere for 6 hours to obtain a precursor;

[0078] S3. Grind the precursor obtained in step S2, perform a second tabletting, place it in a tube furnace, and perform a second sintering for 9 hours at 800° C. in an argon atmosphere to obtain a GdFMoO4 magnetic refrigeration material.

[0079] Example 3

[0080] A method for preparing a gadolinium-based molybdate magnetic refrigeration material comprises the following steps:

[0081] S1. Preparation of mixed material: Gd2O3, GdF3 and MoO3 were mixed, and an appropriate amount of anhydrous ethanol was added, followed by ball milling for 6 hours and drying to obtain a mixed material;

[0082] S2, pre-sintering: the mixed material obtained in step S1 is pressed into a sheet for the first time, placed in a tube furnace, and sintered for the first time at 600° C. in an argon atmosphere for 6 hours to obtain a precursor;

[0083] S3. Grind the precursor obtained in step S2, perform a second tabletting, place it in a tube furnace, and perform a second sintering for 6 hours at 900° C. in an argon atmosphere to obtain a GdFMoO4 magnetic refrigeration material.

[0084] Example 4

[0085] A method for preparing a gadolinium-based molybdate magnetic refrigeration material comprises the following steps:

[0086] S1. Preparation of mixed material: Gd2O3, GdF3 and MoO3 were mixed, and an appropriate amount of anhydrous ethanol was added, followed by ball milling for 6 hours and drying to obtain a mixed material;

[0087] S2, pre-sintering: the mixed material obtained in step S1 is pressed into a sheet for the first time, placed in a tube furnace, and sintered for the first time at 700° C. in an argon atmosphere for 6 hours to obtain a precursor;

[0088] S3. Grind the precursor obtained in step S2, perform a second tabletting, place it in a tube furnace, and perform a second sintering for 3 hours at 1000° C. in an argon atmosphere to obtain a GdFMoO4 magnetic refrigeration material.

[0089] Example 5

[0090] A method for preparing a gadolinium-based molybdate magnetic refrigeration material comprises the following steps:

[0091] S1. Precursor preparation: 5 g of GdCl3·6H2O was placed in a muffle furnace, sintered for the first time at 500°C and kept warm for 4 h to obtain GdOCl;

[0092] S2. Preparation of mixed material: GdOCl and MoO3 were mixed evenly in a molar ratio of 1:1, loaded into an alumina crucible, filled with nitrogen and sealed in a quartz tube, placed in a muffle furnace, and sintered for the second time at 900°C for 14 hours to obtain GdClMoO4 magnetic refrigeration material.

[0093] Example 6

[0094] A method for preparing a gadolinium-based molybdate magnetic refrigeration material comprises the following steps:

[0095] S1. Precursor preparation: 5 g of GdCl3·6H2O was placed in a muffle furnace, sintered for the first time at 500°C and kept warm for 4 h to obtain GdOCl;

[0096] S2. Preparation of mixed material: GdOCl and MoO3 are mixed evenly in a molar ratio of 1:1, loaded into an alumina crucible, filled with nitrogen and sealed in a quartz tube, placed in a muffle furnace, sintered for the second time at 800°C and kept warm for 20 hours to obtain GdClMoO4 magnetic refrigeration material.

[0097] Example 7

[0098] A method for preparing a gadolinium-based molybdate magnetic refrigeration material comprises the following steps:

[0099] S1. Precursor preparation: 5 g of GdCl3·6H2O was placed in a muffle furnace, sintered for the first time at 500°C and kept warm for 4 h to obtain GdOCl;

[0100] S2. Preparation of mixed material: GdOCl and MoO3 were mixed evenly in a molar ratio of 1:1, loaded into an alumina crucible, filled with nitrogen and sealed in a quartz tube, placed in a muffle furnace, sintered for the second time at 850°C and kept warm for 18 hours to obtain GdClMoO4 magnetic refrigeration material.

[0101] Example 8

[0102] A method for preparing a gadolinium-based molybdate magnetic refrigeration material comprises the following steps:

[0103] S1. Precursor preparation: 5 g of GdCl3·6H2O was placed in a muffle furnace, sintered for the first time at 500°C and kept warm for 4 h to obtain GdOCl;

[0104] S2. Preparation of mixed material: GdOCl and MoO3 are mixed evenly in a molar ratio of 1:1, loaded into an alumina crucible, filled with nitrogen and sealed in a quartz tube, placed in a muffle furnace, sintered for the second time at 1000°C and kept warm for 10 hours to obtain GdClMoO4 magnetic refrigeration material.

[0105] Comparative Example 1

[0106] The preparation method of the magnetic refrigeration material in this comparative example is different from that in Example 1, the first sintering temperature in step S2 is 400° C., and the second sintering temperature in step S3 is 500° C., and the rest are the same.

[0107] Comparative Example 2

[0108] The preparation method of the magnetic refrigeration material in this comparative example is different from that in Example 1, the first sintering temperature in step S2 is 900° C., and the second sintering temperature in step S3 is 1200° C., and the rest are the same.

[0109] Comparative Example 3

[0110] The preparation method of the magnetic refrigeration material in this comparative example is different from that in Example 5, the first sintering temperature in step S1 is 500° C., and the second sintering temperature in step S2 is 600° C., and the rest are the same.

[0111] Comparative Example 4

[0112] The preparation method of the magnetic refrigeration material in this comparative example is different from that in Example 5, the first sintering temperature in step S1 is 900° C., and the second sintering temperature in step S2 is 1100° C., and the rest are the same.

[0113] Table 1

[0114]

[0115] Table 2

[0116]

[0117]

[0118] Performance Test:

[0119] (1) The GdFMoO4 and GdClMoO4 samples prepared in each example were subjected to X-ray powder diffraction phase analysis using a Brucker D8A A25 X-ray diffractometer (XRD).

[0120] (2) The GdFMoO4 and GdClMoO4 samples prepared in Examples 1 and 5 were subjected to magnetocaloric performance testing and analysis. The magnetic entropy change (-ΔS M ), the maximum value of the magnetic entropy change obtained is the maximum magnetic entropy change (-ΔS max ), where the magnetization intensity-temperature curve is obtained from the isothermal magnetization curve.

[0121] Maxwell relations:

[0122]

[0123] Among them, ΔS M (T,H) is the magnetic entropy change, M is the magnetization, T is the temperature, and H is the applied magnetic field.

[0124] Figure 1 The crystal structure diagram of the gadolinium-based molybdate magnetic refrigeration material GdFMoO4 of the present invention is shown in the attached figure. Figure 2 As shown, it can be seen that the samples of Examples 1-4 have good matching with the standard spectra, indicating that Examples 1-4 have all produced GdFMoO4 magnetic refrigeration materials. Among them, the XRD spectra of the samples in Examples 2-4 have a small amount of impurity peaks near 33°, and the XRD spectra of the sample in Example 3 have impurity peaks near 24° and 26°, indicating that there are fewer impurity phases in these materials, while the XRD spectra of the sample in Example 1 have good matching with the standard spectra, indicating that the sample has high purity, is composed of a single GdFMoO4 phase, belongs to the monoclinic system, has a space group of P21 / c, and a unit cell parameter α=γ=90°, β=106°. This indicates that the sintering temperature and sintering time need to be adjusted during preparation in order to obtain GdFMoO4 with better purity.

[0125] Figure 3It is the X-ray diffraction pattern of GdFMoO4 prepared by Example 1, Comparative Example 1 and Comparative Example 2 of the present invention. It can be seen that the sintering temperature of Comparative Examples 1-2 is too low or too high, which leads to the failure to successfully synthesize the GdFMoO4 magnetic refrigeration material with higher purity. The method of the present invention first forms a precursor by a first sintering, and then performs a second sintering to obtain a gadolinium-based molybdate magnetic refrigeration material. The gadolinium-based molybdate magnetic refrigeration material is prepared by two sinterings, which can effectively improve the reaction activity and the purity of the gadolinium-based molybdate magnetic refrigeration material. High-purity samples reduce the interference of impurities. The higher the purity, the more heat the material may release or absorb during the magnetization and demagnetization process under the magnetic field, which can achieve a higher magnetic entropy change and improve the efficiency of magnetic refrigeration. In the preparation of GdFMoO4 magnetic refrigeration material, the present invention can select the first sintering temperature to be 600-700°C and the first sintering time to be 4-8h, and the second sintering temperature to be 800-1000°C and the second sintering time to be 3-9h. Under the above sintering conditions, a GdFMoO4 magnetic refrigeration material with higher purity can be obtained, thereby improving the magnetic refrigeration efficiency.

[0126] Attached Figure 4 The thermomagnetic curve of the GdFMoO4 sample prepared in Example 1 of the present invention under field cooling (FC) in a 500Oe magnetic field. Figure 5 The isothermal magnetization curve of the GdFMoO4 sample prepared in Example 1 of the present invention at 0.4-1.8K under a 0-50kOe magnetic field. As can be seen from the figure, the magnetization intensity of the material increases rapidly with the increase of the external magnetic field under an external magnetic field of 15kOe, tends to saturation when the magnetic field is 50kOe, and the magnetic phase transition temperature is less than 2K.

[0127] The magnetic entropy change under different magnetic field changes can be calculated based on the isothermal magnetization curves at different temperatures using Maxwell relations. Figure 6 The relationship between the magnetic entropy change and temperature of the GdFMoO4 sample prepared in Example 1 of the present invention under different magnetic field changes. Figure 6 It can be seen that the maximum magnetic entropy change of the material -ΔS max Appears at 1.1K-1.3K. Figure 6 It can be seen that when the magnetic field changes to 10, 20 and 50 kOe, the maximum magnetic entropy change values ​​are 14.9 J·kg -1 ·K -1 、32.3J·kg -1 ·K -1 and 46.5 J·kg -1 ·K -1 , it has a large magnetocaloric effect in a low external magnetic field (especially ≤50kOe).

[0128] Figure 7 This is a crystal structure diagram of the magnetic refrigeration material GdClMoO4 of the present invention. Figure 8 The XRD spectra of Examples 5-8 show that the samples of Examples 5-8 have good matching with the standard spectra, indicating that GdClMoO4 magnetic refrigeration materials have been prepared in Examples 5-8. The XRD spectra of the sample in Example 6 have impurity peaks near 22°, 29°, and 32°, the XRD spectra of the sample in Example 7 have impurity peaks near 29°, and the XRD spectra of the sample in Example 8 have impurity peaks near 17° and 32°, indicating that there are fewer impurity phases in these materials, and the XRD spectra of the sample in Example 5 have good matching with the standard spectra, indicating that the sample has high purity, is composed of a single GdClMoO4 phase, belongs to the monoclinic system, has a space group of C2 / m, and has a unit cell parameter of α=γ=90°, β=106°. This indicates that the sintering temperature and sintering time need to be adjusted during preparation in order to obtain GdClMoO4 with better purity.

[0129] Fig. 9 It is the X-ray diffraction spectrum of GdClMoO4 prepared by Example 5, Comparative Example 3 and Comparative Example 4 of the present invention. It can be seen that the sintering temperature of Comparative Examples 3-4 is too low or too high, which leads to the failure to successfully synthesize the GdClMoO4 magnetic refrigeration material with higher purity. The method of the present invention first converts the GdX3·nH2O containing crystal water into GdOX by the first sintering, and then sinters it with MoO3 for the second time to obtain the gadolinium-based molybdate magnetic refrigeration material. The gadolinium-based molybdate magnetic refrigeration material is prepared by sintering twice, which can effectively improve the reaction activity and the purity of the gadolinium-based molybdate magnetic refrigeration material. In the preparation of the GdClMoO4 magnetic refrigeration material, the present invention can select the temperature of the first sintering to be 400-600℃ and the time of the first sintering to be 3-6h, and the temperature of the second sintering to be 800-1000℃ and the time of the second sintering to be 10-20h. Under the above sintering conditions, a GdClMoO4 magnetic refrigeration material with higher purity can be obtained to improve the efficiency of magnetic refrigeration.

[0130] Attached Fig.10 The FC thermomagnetic curve of the GdClMoO4 sample prepared in Example 5 of the present invention under a magnetic field of 500Oe. Fig.11 The isothermal magnetization curve of the GdClMoO4 sample prepared in Example 5 of the present invention at 0.4K-1.8K under a magnetic field variation of 0-50kOe is shown in the figure. As can be seen from the figure, the magnetization intensity of the material increases rapidly with the increase of the external magnetic field under an external magnetic field of 15kOe, tends to saturation when the magnetic field is 50kOe, and the magnetic phase transition temperature is less than 2K.

[0131] The magnetic entropy change under different magnetic field changes can be calculated based on the isothermal magnetization curves at different temperatures using Maxwell relations. Fig.12The relationship between the magnetic entropy change and temperature of the GdClMoO4 sample prepared in Example 5 of the present invention under different magnetic field changes. Fig.12 It can be seen that the maximum magnetic entropy change of the material -ΔS max Appears at 1.1K-1.3K. Fig.12 It can be seen that when the magnetic field changes to 10, 20 and 50 kOe, the maximum magnetic entropy change values ​​are 17.4 J·kg -1 ·K -1 、34.0J·kg -1 ·K -1 and 48.2 J·kg -1 ·K -1 It has a large magnetocaloric effect in a low external magnetic field (especially ≤50kOe) and is an ultra-low temperature magnetic refrigeration material with excellent performance.

[0132] In summary, the present invention adopts solid phase reaction sintering to obtain two new types of ultra-low temperature magnetic refrigeration materials. The materials have excellent magnetocaloric properties at ultra-low temperatures and have broad application prospects in the field of ultra-low temperature magnetic refrigeration.

[0133] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A gadolinium-based molybdate magnetic refrigeration material, characterized in that: The invention comprises GdXMoO4, wherein X is F, Cl, Br or I; the magnetic phase transition temperature of the gadolinium-based molybdate magnetic refrigeration material is less than 2K, and the maximum magnetic entropy change of the gadolinium-based molybdate magnetic refrigeration material is greater than or equal to 12J·kg under a magnetic field change of 0-50kOe. -1 ·K -1 .

2. The gadolinium-based molybdate magnetic refrigeration material according to claim 1, characterized in that: Satisfy at least one of the following conditions: Ⅰ. When the magnetic field changes from 0 to 10 kOe, the maximum magnetic entropy change of the gadolinium-based molybdate magnetic refrigeration material is ≥13 J·kg -1 ·K -1 ; II. When the magnetic field changes from 0 to 20 kOe, the maximum magnetic entropy change of the gadolinium-based molybdate magnetic refrigeration material is ≥30 J·kg -1 ·K -1 ; III. When the magnetic field changes from 0 to 30 kOe, the maximum magnetic entropy change of the gadolinium-based molybdate magnetic refrigeration material is ≥32 J·kg -1 ·K -1 ; IV. When the magnetic field changes from 0 to 40 kOe, the maximum magnetic entropy change of the gadolinium-based molybdate magnetic refrigeration material is ≥39 J·kg -1 ·K -1 .

3. The gadolinium-based molybdate magnetic refrigeration material according to claim 1, characterized in that: Satisfy at least one of the following conditions: Ⅰ. The gadolinium-based molybdate magnetic refrigeration material includes GdFMoO4. When the magnetic field changes from 0 to 50 kOe, the maximum magnetic entropy change of GdFMoO4 is ≥14 J·kg -1 ·K -1 ; II. The gadolinium-based molybdate magnetic refrigeration material includes GdClMoO4, and the maximum magnetic entropy change of the GdClMoO4 is ≥17 J·kg under a magnetic field change of 0-50 kOe. -1 ·K -1 .

4. The gadolinium-based molybdate magnetic refrigeration material according to claim 1, characterized in that: Satisfy at least one of the following conditions: Ⅰ. The gadolinium-based molybdate magnetic refrigeration material includes GdFMoO4, and the unit cell information of the GdFMoO4 is as follows: α=γ=90°, β=106°, belonging to the monoclinic system, space group is P21 / c; II. The gadolinium-based molybdate magnetic refrigeration material includes GdClMoO4, and the unit cell information of the GdClMoO4 is as follows: α=γ=90°, β=112°, it belongs to the monoclinic crystal system and its space group is C2 / m.

5. A method for preparing the gadolinium-based molybdate magnetic refrigeration material according to any one of claims 1 to 4, characterized in that: The steps include: S1, mixing Gd2O3, GdX3, MoO3 and a solvent, and sequentially ball milling and drying to obtain a mixture; S2, performing a first tableting and a first sintering on the mixed material in sequence to obtain a precursor; S3, grinding, tableting and sintering the precursor in sequence to obtain the gadolinium-based molybdate magnetic refrigeration material.

6. The method for preparing the gadolinium-based molybdate magnetic refrigeration material according to claim 5, characterized in that: Include at least one of the following: Ⅰ. In step S1, the molar ratio of Gd2O3, GdX3 and MoO3 is Gd2O3:GdX3:MoO3=1:(0.9-1.1):(2-4); II. In step S2, the temperature of the first sintering is 600-700°C, and the time of the first sintering is 4-8h; III. In step S3, the temperature of the second sintering is 800-1000° C., and the time of the second sintering is 3-9 hours.

7. The method for preparing the gadolinium-based molybdate magnetic refrigeration material according to claim 5, characterized in that: In step S1, the GdX3 includes GdF3.

8. A method for producing a gadolinium-based molybdate magnetic refrigeration material according to any one of claims 1 to 4, characterized in that: The steps include: S1, sintering GdX3·nH2O for the first time to obtain GdOX, wherein n in GdX3·nH2O represents that GdX3 contains n molecules of crystal water, and n is 1 to 6; S2, sintering the GdOX and MoO3 for a second time in an inert gas atmosphere to obtain the gadolinium-based molybdate magnetic refrigeration material.

9. The method for preparing the gadolinium-based molybdate magnetic refrigeration material according to claim 8, characterized in that: Include at least one of the following: (A) In step S1, the GdX3·nH2O includes GdF3·6H2O; (B) In step S1, the temperature of the first sintering is 400-600° C., and the time of the first sintering is 3-6 hours; (C) In step S2, the temperature of the second sintering is 800-1000° C., and the time of the second sintering is 10-20 hours; (D) In ​​step S2, the molar ratio of GdOX to MoO3 is 1:(0.9-1.1).

10. Use of the gadolinium-based molybdate magnetic refrigeration material according to any one of claims 1 to 4 in preparing a magnetic refrigeration device.

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