Rare earth europium-based zirconate magnetic refrigeration material, preparation method and application thereof

Abstract

The application belongs to the technical field of magnetic refrigeration, and particularly discloses a rare earth europium-based zirconate magnetic refrigeration material, a preparation method and application thereof. 1‑x M x )(Zr 1‑y N y )O3, wherein M is any one of Ca, Sr or Ba, N is any one of Nb, Ta, Ti or Hf, 0<=x<=0.5, 0<=y<=0.5, and the magnetic phase transition temperature of the rare earth europium-based zirconate magnetic refrigeration material is less than 10K. The magnetic refrigeration material has excellent magnetic heat performance near liquid helium temperature, and is expected to be applied to magnetic refrigeration technology in the liquid helium temperature range; and the preparation method is simple, safe and environmentally friendly, and can be applied to industrial production.

Description

Technical Field

[0001] This invention belongs to the field of magnetic refrigeration technology, and particularly relates to a rare earth europium-based zirconate magnetic refrigeration material, its preparation method and application. Background Technology

[0002] Since the 20th century, cryogenic refrigeration technology has experienced unprecedented development and application, becoming one of the key supporting technologies for modern scientific and technological development. Among these technologies, liquid helium temperature (approximately 4.2K) refrigeration is an indispensable and crucial component of cryogenic refrigeration, playing a vital technical supporting role in fields such as low-temperature physics, low-temperature superconductivity, space exploration, aerospace, nuclear magnetic resonance, magnetic levitation, and military applications. Currently, the mainstream method for achieving liquid helium temperatures is the use of the Gifford-McMahon (GM) cryostat, but its refrigeration efficiency is only about 1% of the Carnot cycle efficiency. Therefore, how to effectively improve the refrigeration efficiency of the GM cryostat is a critical issue that urgently needs to be addressed in related technological fields.

[0003] Magnetic refrigeration is a novel solid-state refrigeration technology that utilizes the magnetocaloric effect (MCE) of magnetic materials to achieve cooling. The magnetocaloric effect is an intrinsic property of magnetic materials, meaning that when an external magnetic field changes, the magnetic entropy of the material changes, causing the material to absorb or release heat from the environment, thus achieving a cooling effect. Magnetic refrigeration technology has many advantages, including high efficiency and energy saving, environmental friendliness, miniaturization, and stability and reliability, and is expected to become a new generation of refrigeration technology to replace traditional gas compression refrigeration. The magnetic refrigeration material is the source of cooling in the magnetic refrigeration system. Developing magnetocaloric materials with a large magnetocaloric effect near the liquid helium temperature is key to realizing the application of magnetic refrigeration technology in the liquid helium temperature range.

[0004] Various magnetic refrigeration materials have been disclosed in the prior art, but they still suffer from problems such as low magnetocaloric effect and complex preparation processes. For example, CN107910151A discloses a non-rare earth magnetic refrigeration material KBBFO and its preparation method, with the chemical formula KBa8Fe. 12 (Bi 6-x Fe x )O 38 (x=0~5), this material is prepared by a hydrothermal method, which has the advantages of simple process and short cycle, but its maximum magnetic entropy change under a magnetic field change of 0-1T is only about 0.23J·kg. -1 ·K -1 CN111403137A discloses a rare-earth-based oxide magnetic refrigeration material and its preparation method. The chemical formula of the material is RE2ZnMnO6 (RE = any one or more elements selected from Gd, Tb, Dy, Ho, Er, and Tm). This material is prepared by the sol-gel method, with a phase transition temperature between 4.5 and 5.8 K. Under a magnetic field change of 0-5 T, its isothermal magnetic entropy change is only between 13.2 and 15.2 J·kg.-1 ·K -1 Moreover, the material preparation process is complicated and requires multiple calcinations to obtain.

[0005] Therefore, developing liquid helium temperature-range magnetic refrigeration materials with a large magnetocaloric effect driven by a low magnetic field near liquid helium temperature, and with a simple preparation process, short cycle, and suitability for large-scale production, is the key to promoting the large-scale application of liquid helium temperature-range magnetic refrigeration technology, and has significant economic value and important practical significance. Summary of the Invention

[0006] In view of the problems of low magnetocaloric effect and complex preparation process of the magnetic refrigeration materials involved in the above-mentioned prior art, the present invention will provide a rare earth europium-based zirconate magnetic refrigeration material, its preparation method and application.

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

[0008] In a first aspect, the present invention provides a rare-earth europium-based zirconate magnetic refrigeration material, the chemical formula of which is (Eu... 1-x M x (Zr) 1-y N y The rare earth europium-based zirconate magnetic refrigeration material has the following chemical formula: (Eu)O3, wherein M is any one of Ca, Sr, or Ba, N is any one of Nb, Ta, Ti, or Hf, 0 ≤ x ≤ 0.5, 0 ≤ y ≤ 0.5, and the magnetic phase transition temperature of the rare earth europium-based zirconate magnetic refrigeration material is less than 10 K. 1-x M x (Zr) 1-y N y Rare earth europium-based zirconates of O3 have magnetic phase transition temperatures near those of liquid helium, and their magnetic phase transitions are accompanied by significant magnetocaloric effects. In this invention, the magnetic phase transition temperature refers to the temperature at which a material transitions from a paramagnetic state to an antiferromagnetic or ferromagnetic state.

[0009] As a preferred embodiment of the rare-earth europium-based zirconate magnetic refrigeration material of the present invention, the rare-earth europium-based zirconate magnetic refrigeration material includes EuZrO3, Eu... 0.8 Sr 0.2 ZrO3, EuZr 0.875 Nb 0.125 O3, Eu 0.7 Ba 0.3 ZrO3 or EuZr 0.875 Ta 0.125 At least one of O3.

[0010] As a preferred embodiment of the rare earth europium-based zirconate magnetic refrigeration material of the present invention, the magnetic phase transition temperature of the rare earth europium-based zirconate magnetic refrigeration material is 3-4.5K, specifically, it can be 3K, 3.2K, 3.4K, 3.6K, 3.8K, 4.0K, 4.2K, 4.4K, 4.5K, or any combination of these values.

[0011] In a preferred embodiment of the rare-earth europium-based zirconate magnetic refrigeration material of the present invention, at the magnetic phase transition temperature, when the magnetic field changes by 0-1T, the maximum magnetic entropy change of the rare-earth europium-based zirconate magnetic refrigeration material is ≥3.5 J·kg. -1 ·K -1 Further optimization of 4-15 J·kg -1 ·K -1 Specifically, it can be 4 J·kg -1 ·K -1 5J·kg -1 ·K -1 6J·kg -1 ·K -1 7J·kg -1 ·K -1 8J·kg -1 ·K -1 9J·kg -1 ·K -1 10J·kg -1 ·K -1 11J·kg -1 ·K -1 12J·kg -1 ·K -1 13J·kg -1 ·K -1 14 J·kg -1 ·K -1 15J·kg -1 ·K -1 Or a range of any two of these values. The magnetocaloric properties of the magnetic refrigeration material are tested and analyzed. Using Maxwell's relation, the magnetic entropy change under different magnetic field variations can be calculated based on the isothermal magnetization curves at different temperatures. Furthermore, the maximum magnetic entropy change of the magnetic refrigeration material can be obtained from the curves showing the change in magnetic entropy with temperature under different magnetic field variations.

[0012] As a preferred embodiment of the rare-earth europium-based zirconate magnetic refrigeration material of the present invention, at a temperature of 4.5K and a magnetic field change of 0-1T, the maximum magnetic entropy change of the rare-earth europium-based zirconate magnetic refrigeration material is ≥3.5J·kg. -1 ·K -1 .

[0013] In a preferred embodiment of the rare-earth europium-based zirconate magnetic refrigeration material of the present invention, at the magnetic phase transition temperature, when the magnetic field changes by 0-2T, the maximum magnetic entropy change of the rare-earth europium-based zirconate magnetic refrigeration material is ≥12.8 J·kg. -1 ·K -1 Further optimization of 13-40 J·kg -1 ·K -1 Specifically, it can be 13 J·kg -1 ·K -1 15J·kg -1 ·K -1 17 J·kg -1 ·K -1 19 J·kg -1 ·K -1 21 J·kg -1 ·K -1 23J·kg -1 ·K -1 25J·kg -1 ·K -1 27 J·kg -1 ·K -1 29 J·kg -1 ·K -1 31J·kg -1 ·K -1 33J·kg -1 ·K -1 35J·kg -1 ·K -1 37J·kg -1 ·K -1 39J·kg -1 ·K -1 40J·kg -1 ·K -1 , or a range consisting of any two of these values.

[0014] In a preferred embodiment of the rare-earth europium-based zirconate magnetic refrigeration material of the present invention, at a temperature of 4.5K and a magnetic field change of 0-2T, the maximum magnetic entropy change of the rare-earth europium-based zirconate magnetic refrigeration material is ≥12.8 J·kg. -1 ·K -1 .

[0015] In a preferred embodiment of the rare-earth europium-based zirconate magnetic refrigeration material of the present invention, when the magnetic field changes by 0-5T at the magnetic phase transition temperature, the maximum magnetic entropy change of the rare-earth europium-based zirconate magnetic refrigeration material is ≥20 J·kg. -1 ·K -1 Further optimization of 21-40 J·kg -1 ·K-1 Specifically, it can be 21 J·kg -1 ·K -1 23J·kg -1 ·K -1 25J·kg -1 ·K -1 27 J·kg -1 ·K -1 29 J·kg -1 ·K -1 31J·kg -1 ·K -1 33J·kg -1 ·K -1 35J·kg -1 ·K -1 37J·kg -1 ·K -1 39J·kg -1 ·K -1 40J·kg -1 ·K -1 , or a range consisting of any two of these values.

[0016] As a preferred embodiment of the rare-earth europium-based zirconate magnetic refrigeration material of the present invention, when the magnetic field changes from 0 to 1T, the magnetic refrigeration capacity of the rare-earth europium-based zirconate magnetic refrigeration material is ≥10.9 J·kg. -1 Further optimization of 11-20 J·kg -1 Cooling capacity is another key parameter for evaluating the magnetocaloric effect of materials; it is a measure of how much heat can be transferred in an ideal refrigeration cycle. The magnetic cooling capacity of this invention can be obtained according to the formula for magnetic cooling capacity (RC):

[0017]

[0018] In the formula, RC corresponds to the half-width at half-maximum (WHM) of the magnetic entropy change curve, T1 and T2 correspond to the temperatures at the temperature boundaries of the WHM of the magnetic entropy change curve, and ΔS M This is a magnetic entropy change.

[0019] As a preferred embodiment of the rare-earth europium-based zirconate magnetic refrigeration material of the present invention, when the magnetic field changes from 0 to 2T, the magnetic refrigeration capacity of the rare-earth europium-based zirconate magnetic refrigeration material is ≥44.5 J·kg. -1 Further optimization of 45-60 J·kg -1 The magnetic refrigeration material of this invention exhibits a large magnetocaloric effect driven by a low magnetic field near the liquid helium temperature.

[0020] As a preferred embodiment of the rare earth europium-based zirconate magnetic refrigeration material of the present invention, the crystal of the rare earth europium-based zirconate magnetic refrigeration material has an orthorhombic crystal system and its space group is Pbnm.

[0021] Secondly, the present invention provides a method for preparing the rare earth europium-based zirconate magnetic refrigeration material, comprising the following steps:

[0022] (1) According to the general chemical formula (Eu 1-x M x (Zr) 1-y N y The stoichiometric ratio of elements in O3 is taken as Eu2O3, ZrO2, oxides of M, and oxides of N. Eu2O3, ZrO2, oxides of M, oxides of N and reducing agent are ball-milled and dried in sequence to obtain a mixture. The molar ratio of the reducing agent to Eu2O3 is (1.05-1.2):1.

[0023] (2) The mixture is heat-treated in an inert gas atmosphere or a reducing atmosphere to obtain the rare earth europium-based zirconate magnetic refrigeration material; the heat treatment temperature is greater than or equal to 1250°C and the heat treatment time is greater than or equal to 12h.

[0024] In a preferred embodiment of the rare earth europium-based zirconate magnetic refrigeration material of the present invention, in step (1), the reducing agent includes at least one of coke or graphene.

[0025] As a preferred embodiment of the rare earth europium-based zirconate magnetic refrigeration material of the present invention, in step (1), the molar ratio of the reducing agent to Eu2O3 is (1.05-1.2):1, specifically, it can be 1.05:1, 1.1:1, 1.15:1, 1.2:1, or any combination of these values.

[0026] In a preferred embodiment of the rare earth europium-based zirconate magnetic refrigeration material of the present invention, in step (1), the ball milling is carried out in the presence of a solvent, the solvent including at least one of ethanol or water.

[0027] In a preferred embodiment of the rare earth europium-based zirconate magnetic refrigeration material of the present invention, the ball milling time in step (1) is 2-6 hours.

[0028] As a preferred embodiment of the rare earth europium-based zirconate magnetic refrigeration material of the present invention, in step (2), the temperature of the heat treatment is 1275-1325℃, specifically, it can be 1275℃, 1285℃, 1295℃, 1305℃, 1315℃, 1325℃, or any combination of these values.

[0029] As a preferred embodiment of the rare earth europium-based zirconate magnetic refrigeration material of the present invention, in step (2), the heat treatment time is 12-24h, specifically, it can be 12h, 14h, 16h, 18h, 20h, 22h, 24h, or any combination of these values.

[0030] As a preferred embodiment of the rare earth europium-based zirconate magnetic refrigeration material of the present invention, in step (2), the reducing atmosphere is a mixed atmosphere of hydrogen with a volume percentage of 0-5% and inert gas with a volume percentage of 95-100%.

[0031] In a preferred embodiment of the rare-earth europium-based zirconate magnetic refrigeration material of the present invention, the inert gas includes at least one of helium, argon, or nitrogen.

[0032] Thirdly, the present invention also provides a magnetic refrigeration device, comprising the aforementioned rare-earth europium-based zirconate magnetic refrigeration material. The rare-earth europium-based zirconate magnetic refrigeration material of the present invention can undergo a magnetic phase transition near the liquid helium temperature range, accompanied by a significant magnetocaloric effect. Its application in the preparation of magnetic refrigeration devices enables these devices to achieve greater cooling capacity.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The rare earth europium-based zirconate magnetic refrigeration material of the present invention exhibits a significant magnetocaloric effect near the liquid helium temperature and has a high magnetic refrigeration capacity under low magnetic field, and has potential application prospects in the field of magnetic refrigeration in the liquid helium temperature range.

[0035] (2) The preparation method of the present invention can obtain high-quality rare earth europium-based zirconate magnetic refrigeration material with one heat treatment, without the need for multiple high-temperature calcination. The preparation method is simple, safe and environmentally friendly, and has the advantages of energy saving and high efficiency. Moreover, the raw materials used in this material are inexpensive and suitable for industrial production and application. Attached Figure Description

[0036] Figure 1 The rare earth europium-based zirconate magnetic refrigeration material of this invention (Eu 1-x M x (Zr) 1-y N y )Schematic diagram of the crystal structure of O3.

[0037] Figure 2 The X-ray diffraction (XRD) patterns of the rare earth europium zirconate samples prepared in Examples 2, 4, 6 and Comparative Examples 1-3 are shown.

[0038] Figure 3The thermomagnetic curves of the rare earth europium-based zirconate magnetic refrigeration materials prepared in Examples 2, 4, and 6 under a magnetic field of 0.01T, showing zero-field cooling (ZFC) and field-cooled cooling (FC).

[0039] Figure 4 Isothermal magnetization curves of rare earth europium-based zirconate magnetic refrigeration materials prepared in Examples 2, 4, and 6 at different temperatures.

[0040] Figure 5 The graphs show the changes in magnetic entropy of the rare-earth europium-based zirconate magnetic refrigeration materials prepared in Examples 2, 4, and 6 under different magnetic field variations with temperature. Detailed Implementation

[0041] To better illustrate the purpose, technical solution, and advantages of this invention, specific embodiments will be used to further explain the invention below. Unless otherwise specified, the test methods used in the embodiments and / or comparative examples are conventional methods; the materials and reagents used, unless otherwise specified, are commercially available.

[0042] Example 1

[0043] This embodiment provides a method for preparing EuZrO3 magnetic refrigeration material, which specifically includes the following steps:

[0044] (1) Weigh out the corresponding amounts of Eu2O3 and ZrO2 powders according to the stoichiometric ratio in EuZrO3, mix them evenly, and obtain a mixed powder.

[0045] (2) According to the molar ratio of coke:Eu2O3=1.2:1, coke is added to the mixed powder in step (1), an appropriate amount of anhydrous ethanol is added, ball milling is performed for 4 hours and then drying is performed to obtain the mixture.

[0046] (3) The mixture from step (2) is placed in a tube furnace and heat-treated at 1275°C in an argon atmosphere for 12 hours to obtain EuZrO3 magnetic refrigeration material.

[0047] Example 2

[0048] This embodiment provides a method for preparing EuZrO3 magnetic refrigeration material, which specifically includes the following steps:

[0049] (1) Weigh out the corresponding amounts of Eu2O3 and ZrO2 powders according to the stoichiometric ratio in EuZrO3, mix them evenly, and obtain a mixed powder.

[0050] (2) According to the molar ratio of graphene:Eu2O3=1.1:1, add graphene micro powder to the mixed powder in step (1), add an appropriate amount of anhydrous ethanol, ball mill for 4 hours and then dry to obtain a mixture.

[0051] (3) The mixture from step (2) is placed in a tube furnace and heat-treated at 1300°C in a hydrogen-argon mixed gas atmosphere (hydrogen gas fraction of 5%) for 24 hours to obtain EuZrO3 magnetic refrigeration material.

[0052] Example 3

[0053] This embodiment provides an Eu 0.8 Sr 0.2 The preparation method of ZrO3 magnetic refrigeration material specifically includes the following steps:

[0054] (1) According to Eu 0.8 Sr 0.2 Weigh out the corresponding amounts of Eu2O3, ZrO2 and SrO powders according to the stoichiometric ratio of ZrO3, mix them evenly to obtain a mixed powder;

[0055] (2) According to the molar ratio of coke:Eu2O3=1.1:1, coke is added to the mixed powder in step (1), an appropriate amount of anhydrous ethanol is added, ball milling is performed for 4 hours and then drying is performed to obtain the mixture.

[0056] (3) The mixture from step (2) is placed in a tube furnace and heat-treated at 1325°C in a hydrogen-argon mixed gas atmosphere (hydrogen gas fraction of 3%) for 18 hours to obtain Eu. 0.8 Sr 0.2 ZrO3 magnetic refrigeration material.

[0057] Example 4

[0058] This embodiment provides an EuZr 0.875 Nb 0.125 The preparation method of O3 magnetic refrigeration material specifically includes the following steps:

[0059] (1) According to EuZr 0.875 Nb 0.125 Weigh out the corresponding amounts of Eu2O3, ZrO2 and Nb2O5 powders according to the stoichiometric ratio of O3, mix them evenly to obtain a mixed powder;

[0060] (2) According to the molar ratio of graphene:Eu2O3=1.1:1, add graphene micro powder to the mixed powder in step (1), add an appropriate amount of anhydrous ethanol, ball mill for 4 hours and then dry to obtain a mixture.

[0061] (3) The mixture from step (2) was placed in a tube furnace and heat-treated at 1300°C in a hydrogen-argon mixed gas atmosphere (hydrogen gas fraction of 5%) for 24 hours to obtain EuZr. 0.875 Nb 0.125 O3 magnetic refrigeration material.

[0062] Example 5

[0063] This embodiment provides an Eu 0.7 Ba 0.3 The preparation method of ZrO3 magnetic refrigeration material specifically includes the following steps:

[0064] (1) According to Eu 0.7 Ba 0.3 The stoichiometric ratios of Eu2O3, ZrO2 and BaO powders were weighed out respectively, mixed evenly, and a mixed powder was obtained.

[0065] (2) According to the molar ratio of graphene:Eu2O3=1.05:1, add graphene micro powder to the mixed powder in step (1), add an appropriate amount of anhydrous ethanol, ball mill for 4 hours and then dry to obtain the mixture.

[0066] (3) The mixture from step (2) is placed in a tube furnace and heat-treated at 1325°C in a hydrogen-argon mixed gas atmosphere (hydrogen gas fraction of 3%) for 24 hours to obtain Eu. 0.7 Ba 0.3 ZrO3 magnetic refrigeration material.

[0067] Example 6

[0068] This embodiment provides an EuZr 0.875 Ta 0.125 The preparation method of O3 magnetic refrigeration material specifically includes the following steps:

[0069] (1) According to EuZr 0.875 Ta 0.125 Weigh out the corresponding amounts of Eu2O3, ZrO2 and Ta2O5 powders according to the stoichiometric ratio of O3, mix them evenly to obtain a mixed powder;

[0070] (2) According to the molar ratio of graphene:Eu2O3=1.1:1, add graphene micro powder to the mixed powder in step (1), add an appropriate amount of anhydrous ethanol, ball mill for 4 hours and then dry to obtain a mixture.

[0071] (3) The mixture from step (2) was placed in a tube furnace and heat-treated at 1300°C in a hydrogen-argon mixed gas atmosphere (hydrogen gas fraction of 5%) for 24 hours to obtain EuZr. 0.875 Ta 0.125 O3 magnetic refrigeration material.

[0072] Comparative Example 1

[0073] The only difference between this comparative example and Example 1 is that in step (2), the molar ratio of coke to Eu2O3 is coke:Eu2O3 = 1:1, specifically including the following steps:

[0074] (1) Weigh out the corresponding amounts of Eu2O3 and ZrO2 powders according to the stoichiometric ratio in EuZrO3, mix them evenly, and obtain a mixed powder.

[0075] (2) According to the molar ratio of coke:Eu2O3=1:1, coke is added to the mixed powder in step (1), an appropriate amount of anhydrous ethanol is added, ball milling is performed for 4 hours and then drying is performed to obtain the mixture.

[0076] (3) The mixture from step (2) was placed in a tube furnace and heat-treated at 1275°C in an argon atmosphere for 12 hours to obtain a sample of EuZrO3 magnetic refrigeration material.

[0077] Comparative Example 2

[0078] The only difference between this comparative example and Example 2 is that in step (3), the heat treatment time is 6 hours, which specifically includes the following steps:

[0079] (1) Weigh out the corresponding amounts of Eu2O3 and ZrO2 powders according to the stoichiometric ratio in EuZrO3, mix them evenly, and obtain a mixed powder.

[0080] (2) According to the molar ratio of graphene:Eu2O3=1.1:1, add graphene micro powder to the mixed powder in step (1), add an appropriate amount of anhydrous ethanol, ball mill for 4 hours and then dry to obtain a mixture.

[0081] (3) The mixture from step (2) was placed in a tube furnace and heat-treated at 1300°C in a hydrogen-argon mixed gas atmosphere (hydrogen gas fraction of 5%) for 6 hours to obtain EuZrO3 magnetic refrigeration material sample.

[0082] Comparative Example 3

[0083] The only difference between this comparative example and Example 4 is that in step (3), the heat treatment temperature is 1200℃, which specifically includes the following steps:

[0084] (1) According to EuZr 0.875 Nb 0.125 Weigh out the corresponding amounts of Eu2O3, ZrO2 and Nb2O5 powders according to the stoichiometric ratio of O3, mix them evenly to obtain a mixed powder;

[0085] (2) According to the molar ratio of graphene:Eu2O3=1.1:1, add graphene micro powder to the mixed powder in step (1), add an appropriate amount of anhydrous ethanol, ball mill for 4 hours and then dry to obtain a mixture.

[0086] (3) The mixture from step (2) was placed in a tube furnace and heat-treated at 1200°C in a hydrogen-argon mixed gas atmosphere (hydrogen gas fraction of 5%) for 24 hours to obtain EuZr.0.875 Nb 0.125 O3 magnetic refrigeration material.

[0087] X-ray diffraction (XRD) tests were performed on the rare earth europium-based zirconate materials prepared in Examples 2, 4, 6 and Comparative Examples 1-3. The XRD patterns of the obtained samples were compared and analyzed with standard patterns to determine their phase composition.

[0088] XRD results show that the rare-earth europium-based zirconate material belongs to the orthorhombic crystal system with space group Pbnm. Its crystal structure diagram is shown below. Figure 1 As shown. Figure 2 The X-ray diffraction (XRD) patterns of the rare earth europium-based zirconate samples prepared in Examples 2, 4, 6 and Comparative Examples 1-3 are shown below. Figure 2 It can be seen that the rare earth europium-based zirconate (Eu) prepared in Examples 2, 4, and 6... 1-x M x (Zr) 1-y N y The XRD patterns of Eu2O3 all highly matched the standard card for (EuZrO3 phase), with no obvious impurity peaks, indicating that they were all composed of a single phase. However, the XRD patterns of the europium-based zirconate samples prepared in Comparative Examples 1-3 showed obvious impurity diffraction peaks, indicating the presence of impurity phases in the samples, and that they were not composed of a single phase. Furthermore, europium-based zirconate materials could not be effectively prepared in Comparative Example 3. Therefore, when preparing europium-based zirconate materials, the heat treatment temperature should be greater than or equal to 1250℃, and the heat treatment time should be greater than or equal to 12h. The amount of reducing agent should also be greater than the amount of Eu2O3.

[0089] The thermomagnetic curves of the rare earth europium-based zirconates prepared in Examples 1-6 under zero-field cooling (ZFC) and field-cooled cooling (FC) in a magnetic field of 0.01T were tested. The magnetic phase transition temperature of the material can be obtained by taking the first derivative of the ZFC curve. Figure 3 The thermomagnetic curves of rare earth europium-based zirconates prepared in Examples 2, 4, and 6 of this invention under zero-field cooling (ZFC) and field-cooled cooling (FC) in a 0.01T magnetic field are shown. Through testing and analysis, the magnetic phase transition temperatures of the magnetic refrigeration materials prepared in Examples 1-6 are 4.2K, 4.3K, 3.3K, 3.8K, 3.1K, and 3.8K, respectively, all distributed between 3 and 4.5K, which are potential magnetic refrigeration materials in the liquid helium temperature range.

[0090] The isothermal magnetization curves of rare earth europium-based zirconates prepared in Examples 2, 4, and 6 at different temperatures are shown below. Figure 4 As shown. Using Maxwell's relation, the magnetic entropy change under different magnetic field variations can be calculated from the isothermal magnetization curves at different temperatures. Figure 5The figures show the magnetic entropy change versus temperature curves of rare-earth europium-based zirconates prepared in Examples 2, 4, and 6 of this invention under different magnetic field variations; Figure 5 It can be seen that the maximum magnetic entropy change of the material at 4.5K temperature is ≥3.5J·kg when the magnetic field changes by 0-1T. -1 ·K -1 The maximum magnetic entropy change when the magnetic field changes from 0 to 2 T is ≥12.8 J·kg. -1 ·K -1 Its maximum magnetic entropy change is greater than that of many existing liquid helium temperature-range magnetic refrigeration materials.

[0091] Cooling capacity is another key parameter for evaluating the magnetocaloric effect of a material; it is a measure of how much heat can be transferred in an ideal refrigeration cycle. The magnetic cooling capacity of this invention can be obtained using the formula for magnetic cooling capacity (RC):

[0092]

[0093] In the formula, RC corresponds to the half-width at half-maximum (WHM) of the magnetic entropy change curve, T1 and T2 correspond to the temperatures at the temperature boundaries of the WHM of the magnetic entropy change curve, and ΔS M This represents the magnetic entropy change. Using the above formula, the magnetic refrigeration capacity of the rare-earth europium-based zirconates prepared in Examples 2, 4, and 6 under a magnetic field change of 0-1T is calculated to be ≥10.9 J·kg. -1 The magnetic refrigeration capacity under a magnetic field change of 0-2T is ≥44.5J·kg. -1 It demonstrates excellent magnetic refrigeration capabilities.

[0094] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. 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 be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A rare-earth europium-based zirconate magnetic refrigeration material, characterized in that, Its general chemical formula is (Eu) 1-x M x (Zr) 1-y N y O3, where M is any one of Ca, Sr or Ba, N is any one of Nb, Ta, Ti or Hf, and 0 ≤ x ≤0.5, 0< y ≤0.5, the magnetic phase transition temperature of the rare earth europium-based zirconate magnetic refrigeration material is less than 10K; Includes at least one of the following C or D: C. When the magnetic field changes from 0 to 1 T, the magnetic refrigeration capacity of the rare-earth europium-based zirconate magnetic refrigeration material is ≥10.9 J·kg. -1 ; D. When the magnetic field changes from 0 to 2T, the magnetic refrigeration capacity of the rare-earth europium-based zirconate magnetic refrigeration material is ≥44.5 J·kg. -1 .

2. The rare-earth europium-based zirconate magnetic refrigeration material as described in claim 1, characterized in that, The magnetic phase transition temperature of the rare earth europium-based zirconate magnetic refrigeration material is 3-4.5K.

3. The rare-earth europium-based zirconate magnetic refrigeration material as described in claim 2, characterized in that, Includes at least one of the following features, either A or B: A. At a temperature of 4.5 K and a magnetic field change of 0-1 T, the maximum magnetic entropy change of the rare-earth europium-based zirconate magnetic refrigeration material is ≥3.5 J·kg. -1 ·K -1 ; B. At a temperature of 4.5K and a magnetic field change of 0-2T, the maximum magnetic entropy change of the rare-earth europium-based zirconate magnetic refrigeration material is ≥12.8 J·kg. -1 ·K -1 .

4. The rare-earth europium-based zirconate magnetic refrigeration material as described in claim 1, characterized in that, The rare-earth europium-based zirconate magnetic refrigeration material has an orthorhombic crystal system with space group [missing information]. Pbnm .

5. A method for preparing the rare-earth europium-based zirconate magnetic refrigeration material according to any one of claims 1-4, characterized in that, Includes the following steps: (1) According to the general chemical formula (Eu) 1-x M x (Zr) 1-y N y The stoichiometric ratio of elements in O3 is taken as Eu2O3, ZrO2, oxides of M, and oxides of N. Eu2O3, ZrO2, oxides of M, oxides of N, and a reducing agent are sequentially ball-milled and dried to obtain a mixture. The molar ratio of the reducing agent to Eu2O3 is (1.05-1.2):

1. The reducing agent includes at least one of coke or graphene. (2) The mixture is heat-treated in an inert gas atmosphere or a reducing atmosphere to obtain the rare earth europium-based zirconate magnetic refrigeration material; the heat treatment temperature is greater than or equal to 1250°C and the heat treatment time is greater than or equal to 12h.

6. The preparation method of the rare earth europium-based zirconate magnetic refrigeration material as described in claim 5, characterized in that, In step (1), the ball milling time is 2-6 hours.

7. The method for preparing the rare-earth europium-based zirconate magnetic refrigeration material as described in claim 5, characterized in that, Includes at least one of the following EG: E. In step (2), the temperature of the heat treatment is 1275-1325℃; F. In step (2), the heat treatment time is 12-24 hours; G. In step (2), the reducing atmosphere is a mixture of hydrogen gas with a volume percentage of 0-5% and inert gas with a volume percentage of 95-100%.

8. A magnetic refrigeration device, characterized in that, Including the rare earth europium-based zirconate magnetic refrigeration material as described in any one of claims 1-4.

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