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

Abstract

The invention belongs to the technical field of magnetic refrigeration, and particularly discloses a rare earth europium-based zirconate magnetic refrigeration material and a preparation method and application thereof. The general chemical formula of the rare earth europium-based zirconate magnetic refrigeration material is (Eu1-xMx) (Zr1-yNy) O3, M is any one of Ca, Sr or Ba, N is any one of Nb, Ta, Ti or Hf, x is more than or equal to 0 and less than or equal to 0.5, y is more than or equal to 0 and less than or equal to 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 shows excellent magnetocaloric performance near the liquid helium temperature, and is expected to be applied to the liquid helium temperature zone magnetic refrigeration technology; and the preparation method is simple in process, safe and environment-friendly, and can be applied to industrial production.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnetic refrigeration, and in particular relates to a rare earth europium-based zirconate magnetic refrigeration material and a preparation method and application thereof. Background Art

[0002] Since the 20th century, cryogenic refrigeration technology has achieved unprecedented development and application, and has become one of the key supporting technologies for the development of modern science and technology. Among them, refrigeration in the liquid helium temperature range (about 4.2K) is an indispensable and important component of cryogenic refrigeration, and plays an important technical supporting role in the fields of low-temperature physics, low-temperature superconductivity, space exploration, aerospace, nuclear magnetic resonance, magnetic levitation, military industry, etc. At present, the mainstream method for obtaining liquid helium temperature is to use the Gifford-McMahon (GM) refrigerator, but its refrigeration efficiency is only about 1% of the Carnot cycle efficiency. Therefore, how to effectively improve the refrigeration efficiency of the GM refrigerator is a key problem that needs to be solved urgently in the relevant technical field.

[0003] Magnetic refrigeration is a new type of solid-state refrigeration technology that uses the magnetocaloric effect (MCE) of magnetic materials to achieve refrigeration. The magnetocaloric effect is an intrinsic property of magnetic materials themselves. It means that when the external magnetic field changes, the magnetic entropy of the magnetic material changes, causing the material itself to absorb or release heat from the outside world, thereby achieving a cooling effect. Magnetic refrigeration technology has many advantages such as high efficiency and energy saving, green environmental protection, miniaturization, and stability and reliability. It is expected to become a new generation of refrigeration technology to replace traditional gas compression refrigeration. Magnetic refrigeration materials are the source of cooling capacity of magnetic refrigeration systems. The development of magnetocaloric effect materials with a large magnetocaloric effect near the temperature of liquid helium is the key to realizing the application of magnetic refrigeration technology in the liquid helium temperature range.

[0004] There are many magnetic refrigeration materials disclosed in the prior art, but they still have problems such as low magnetocaloric effect and complicated preparation process. For example, CN107910151A discloses a non-rare earth magnetic refrigeration material KBBFO and its preparation method, whose chemical formula is KBa8Fe 12 (Bi 6-x Fe x )O 38 (x = 0 ~ 5), the material is prepared by hydrothermal method, which has the advantages of simple process and short cycle, but its maximum magnetic entropy change under 0-1T magnetic field change is only about 0.23J kg -1 ·K -1 CN111403137A discloses a rare earth oxide magnetic refrigeration material and its preparation method. The material has the chemical formula RE2ZnMnO6 (RE = any one or several elements among Gd, Tb, Dy, Ho, Er and Tm). The material is prepared by the sol-gel method, with a phase transition temperature between 4.5 and 5.8 K. Under a magnetic field variation 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, the development of liquid helium temperature range magnetic refrigeration materials that have a large magnetocaloric effect driven by low magnetic fields near liquid helium temperature, with a simple preparation process, short cycle, and suitable 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 response to the problems of low magnetocaloric effect and complex preparation process of magnetic refrigeration materials involved in the above-mentioned prior art, the present invention will provide a rare earth europium-based zirconate magnetic refrigeration material and its preparation method and application.

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

[0008] In the 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 )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 chemical formula of the present invention is (Eu 1-x M x )(Zr 1-y N y )O3 rare earth europium zirconate has a magnetic phase transition temperature near liquid helium, and its magnetic phase transition is accompanied by a large magnetocaloric effect. The magnetic phase transition temperature in this invention refers to the temperature at which the material changes from a paramagnetic state to an antiferromagnetic state or a ferromagnetic state.

[0009] As a preferred embodiment of the rare earth europium zirconate magnetic refrigeration material of the present invention, the rare earth europium 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 a range consisting of any two of these values.

[0011] As 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 from 0 to 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 , further preferably 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 , 11 J·kg -1 ·K -1 , 12 J·kg -1 ·K -1 , 13 J·kg -1 ·K -1 , 14 J·kg -1 ·K -1 , 15J·kg -1 ·K -1 , or a range consisting of any two of these values. The magnetocaloric properties of magnetic refrigeration materials are tested and analyzed. The magnetic entropy change under different magnetic field changes can be calculated based on the isothermal magnetization curves at different temperatures using Maxwell's relations. The maximum magnetic entropy change of the magnetic refrigeration material can be obtained based on the curve of magnetic entropy change versus temperature under different magnetic field changes.

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

[0013] As 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 from 0 to 2T, the maximum magnetic entropy change of the rare earth europium-based zirconate magnetic refrigeration material is ≥12.8 J·kg -1 ·K -1 , more preferably 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 , 23 J·kg -1 ·K -1 , 25J·kg -1 ·K -1 , 27 J·kg -1 ·K -1 , 29 J·kg -1 ·K -1 , 31 J·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] As a preferred embodiment of the rare earth europium zirconate magnetic refrigeration material of the present invention, when the temperature is 4.5K and the magnetic field changes from 0 to 2T, the maximum magnetic entropy change of the rare earth europium zirconate magnetic refrigeration material is ≥12.8 J·kg -1 ·K -1 .

[0015] As 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 from 0 to 5T, the maximum magnetic entropy change of the rare earth europium-based zirconate magnetic refrigeration material is ≥20 J·kg -1 ·K -1 , further preferably 21-40 J·kg -1 ·K-1 , specifically, it can be 21 J·kg -1 ·K -1 , 23 J·kg -1 ·K -1 , 25J·kg -1 ·K -1 , 27 J·kg -1 ·K -1 , 29 J·kg -1 ·K -1 , 31 J·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 zirconate magnetic refrigeration material of the present invention, when the magnetic field changes from 0 to 1 T, the magnetic refrigeration capacity of the rare earth europium zirconate magnetic refrigeration material is ≥10.9 J·kg -1 , further preferably 11-20 J·kg -1 Refrigeration 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 refrigeration capacity of the present invention can be obtained according to the magnetic refrigeration capacity (RC) formula:

[0017]

[0018] Where RC corresponds to the half-width area of ​​the magnetic entropy change curve, T1 and T2 correspond to the temperature at the temperature boundary of the half-width of the magnetic entropy change curve, and △S M is the magnetic entropy change.

[0019] As a preferred embodiment of the rare earth europium 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 zirconate magnetic refrigeration material is ≥44.5 J·kg -1 , further preferably 45-60 J·kg -1 The magnetic refrigeration material of the present invention has the characteristics of large magnetocaloric effect driven by low magnetic field near the temperature of liquid helium.

[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] In a second aspect, 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 chemical formula (Eu 1-x M x )(Zr 1-y N y ) The stoichiometric ratio of the elements in O3 is Eu2O3, ZrO2, M oxide, and N oxide, and Eu2O3, ZrO2, M oxide, N oxide, and a reducing agent are ball-milled and dried in sequence to obtain a mixed material; the molar ratio of the reducing agent to Eu2O3 is (1.05-1.2):1;

[0023] (2) heat-treating the mixed material under 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 12 hours.

[0024] As 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 a range consisting of any two of these values.

[0026] As 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, and the solvent includes at least one of ethanol or water.

[0027] As a preferred embodiment of the rare earth europium-based zirconate magnetic refrigeration material of the present invention, in step (1), the ball milling time 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 heat treatment temperature is 1275-1325°C, specifically, it can be 1275°C, 1285°C, 1295°C, 1305°C, 1315°C, 1325°C, or a range consisting of any two 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 12-24 hours, specifically, it can be 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, 24 hours, or a range consisting of any two 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 0-5% by volume of hydrogen and 95-100% by volume of an inert gas.

[0031] As 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] In a third aspect, the present invention further provides a magnetic refrigeration device comprising the rare earth europium zirconate magnetic refrigeration material. The rare earth europium 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. Application of the material in the manufacture of a magnetic refrigeration device can achieve a greater refrigeration 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 temperature of liquid helium and has a high magnetic refrigeration capacity under low magnetic fields, 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 by a single heat treatment without the need for multiple high-temperature calcinations. The preparation method is simple, the preparation process is safe and environmentally friendly, and it has the advantages of energy saving and high efficiency. In addition, the raw materials used in the material are low in cost and are suitable for industrial production and application. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

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

[0040] Figure 5 The graphs are of the change in magnetic entropy versus temperature for the rare earth europium-based zirconate magnetic refrigeration materials prepared in Examples 2, 4, and 6 under different magnetic field conditions. DETAILED DESCRIPTION

[0041] To better illustrate the objectives, technical solutions, and advantages of the present invention, the present invention will be further described below with reference to specific examples. The experimental methods used in the examples and / or comparative examples are conventional methods unless otherwise specified; the materials and reagents used are commercially available unless otherwise specified.

[0042] Example 1

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

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

[0045] (2) adding coke to the mixed powder of step (1) according to the molar ratio of coke:Eu2O3=1.2:1, adding an appropriate amount of anhydrous ethanol, ball milling for 4 hours and then drying to obtain a mixture;

[0046] (3) The mixture of step (2) was placed in a tube furnace and heat treated at 1275° C. in an argon atmosphere for 12 h to obtain EuZrO 3 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 corresponding amounts of Eu2O3 and ZrO2 powder according to the stoichiometric ratio in EuZrO3, mix them evenly, and obtain a mixed powder;

[0050] (2) adding graphene powder to the mixed powder of step (1) according to the molar ratio of graphene:Eu2O3=1.1:1, adding an appropriate amount of anhydrous ethanol, ball milling for 4 hours and then drying to obtain a mixture;

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

[0052] Example 3

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

[0054] (1) According to Eu 0.8 Sr 0.2 The stoichiometric ratio in ZrO3 is to weigh the corresponding amount of Eu2O3, ZrO2 and SrO powder respectively, mix them evenly to obtain a mixed powder;

[0055] (2) adding coke to the mixed powder of step (1) according to the molar ratio of coke:Eu2O3=1.1:1, adding an appropriate amount of anhydrous ethanol, ball milling for 4 hours and then drying to obtain a mixture;

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

[0057] Example 4

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

[0059] (1) According to EuZr 0.875 Nb 0.125 The stoichiometric ratio in O3 was respectively weighed out in corresponding amounts of Eu2O3, ZrO2 and Nb2O5 powders, and mixed evenly to obtain a mixed powder;

[0060] (2) adding graphene powder to the mixed powder of step (1) according to the molar ratio of graphene:Eu2O3=1.1:1, adding an appropriate amount of anhydrous ethanol, ball milling for 4 hours and then drying to obtain a mixture;

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

[0062] Example 5

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

[0064] (1) According to Eu 0.7 Ba 0.3 The stoichiometric ratio in ZrO3 is to weigh the corresponding amount of Eu2O3, ZrO2 and BaO powder respectively, mix them evenly to obtain a mixed powder;

[0065] (2) adding graphene powder to the mixed powder of step (1) according to the molar ratio of graphene:Eu2O3=1.05:1, adding an appropriate amount of anhydrous ethanol, ball milling for 4 hours and then drying to obtain a mixture;

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

[0067] Example 6

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

[0069] (1) According to EuZr 0.875 Ta 0.125 The stoichiometric ratio in O3 is respectively weighed out in corresponding amounts of Eu2O3, ZrO2 and Ta2O5 powders, mixed evenly to obtain a mixed powder;

[0070] (2) adding graphene powder to the mixed powder of step (1) according to the molar ratio of graphene:Eu2O3=1.1:1, adding an appropriate amount of anhydrous ethanol, ball milling for 4 hours and then drying to obtain a mixture;

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

[0072] Comparative Example 1

[0073] Compared with Example 1, this comparative example differs only in that in step (2), the molar ratio of coke to Eu2O3 is coke:Eu2O3=1:1, and specifically comprises the following steps:

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

[0075] (2) adding coke to the mixed powder of step (1) according to the molar ratio of coke:Eu2O3=1:1, adding an appropriate amount of anhydrous ethanol, ball milling for 4 hours and then drying to obtain a mixture;

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

[0077] Comparative Example 2

[0078] This comparative example is different from Example 2 only in that in step (3), the heat treatment time is 6 h, and specifically includes the following steps:

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

[0080] (2) adding graphene powder to the mixed powder of step (1) according to the molar ratio of graphene:Eu2O3=1.1:1, adding an appropriate amount of anhydrous ethanol, ball milling for 4 hours and then drying to obtain a mixture;

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

[0082] Comparative Example 3

[0083] This comparative example is different from Example 4 only in that in step (3), the heat treatment temperature is 1200° C., and specifically includes the following steps:

[0084] (1) According to EuZr 0.875 Nb 0.125 The stoichiometric ratio in O3 was respectively weighed out in corresponding amounts of Eu2O3, ZrO2 and Nb2O5 powders, and mixed evenly to obtain a mixed powder;

[0085] (2) adding graphene powder to the mixed powder of step (1) according to the molar ratio of graphene:Eu2O3=1.1:1, adding an appropriate amount of anhydrous ethanol, ball milling for 4 hours and then drying to obtain a mixture;

[0086] (3) The mixture of step (2) was placed in a tube furnace and heat treated at 1200°C in a hydrogen-argon mixed gas atmosphere (hydrogen gas volume fraction is 5%) for 24 hours to obtain EuZr0.875 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, and the XRD patterns of the obtained samples were compared and analyzed with the standard patterns to determine their phase compositions.

[0088] From the XRD test results, it can be seen that the crystal of rare earth europium-based zirconate material belongs to the orthorhombic system, the space group is Pbnm, and its crystal structure diagram is as follows Figure 1 shown. Figure 2 X-ray diffraction (XRD) patterns of the rare earth europium zirconate samples prepared in Examples 2, 4, 6 and Comparative Examples 1-3; Figure 2 It can be seen that the rare earth europium zirconate (Eu 1-x M x )(Zr 1-y N y )O3's XRD patterns are highly matched with the (EuZrO3 phase) standard card, with no obvious miscellaneous peaks, indicating that they are all composed of a single phase. However, the XRD patterns of the europium zirconate samples prepared in Comparative Examples 1-3 have obvious miscellaneous diffraction peaks, indicating that there are impurity phases in the samples and they are not composed of a single phase. In addition, the europium zirconate material cannot be effectively prepared in Comparative Example 3. Therefore, when preparing the europium zirconate material, the heat treatment temperature should be greater than or equal to 1250°C, the heat treatment time should be greater than or equal to 12 hours, and the amount of the reducing agent should be greater than the amount of Eu2O3.

[0089] The thermomagnetic curves of the rare earth europium zirconates prepared in Examples 1-6 under zero field cooling (ZFC) and field cooling (FC) in a 0.01 T magnetic field were tested, and the magnetic phase transition temperature of the material can be obtained by the first-order derivative of the ZFC curve. Figure 3 These are the zero-field cooling (ZFC) and field cooling (FC) thermomagnetic curves of the rare earth europium-based zirconates prepared in Examples 2, 4, and 6 of the present invention under a 0.01T magnetic field. Through testing and analysis, it is obtained that 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, indicating that they are potential magnetic refrigeration materials in the liquid helium temperature range.

[0090] The isothermal magnetization curves of the rare earth europium zirconates prepared in Examples 2, 4, and 6 at different temperatures are shown in FIG. Figure 4 As shown in Figure 2. Using Maxwell's relationship and the isothermal magnetization curves at different temperatures, the magnetic entropy change under different magnetic field changes can be calculated. Figure 5The curves of magnetic entropy change versus temperature of the rare earth europium zirconate prepared in Examples 2, 4, and 6 of the present invention under different magnetic field changes are shown; Figure 5 It can be seen that the maximum magnetic entropy change of the material at 4.5K when the magnetic field changes from 0 to 1T is ≥3.5J·kg -1 ·K -1 ; When the magnetic field changes from 0 to 2T, the maximum magnetic entropy change is ≥12.8J·kg -1 ·K -1 , its maximum magnetic entropy change is greater than that of many liquid helium temperature zone magnetic refrigeration materials disclosed in the prior art.

[0091] Refrigeration 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 refrigeration capacity of the present invention can be obtained according to the magnetic refrigeration capacity (RC) formula:

[0092]

[0093] Where RC corresponds to the half-width area of ​​the magnetic entropy change curve, T1 and T2 correspond to the temperature at the temperature boundary of the half-width of the magnetic entropy change curve, and △S M The magnetic entropy change is calculated by the above formula to obtain the magnetic refrigeration capacity of the rare earth europium zirconate prepared in Examples 2, 4, and 6 under a magnetic field change of 0-1T ≥ 10.9 J·kg -1 , the magnetic refrigeration capacity under the magnetic field change of 0-2T is ≥44.5J·kg -1 , showing excellent magnetic refrigeration capability.

[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 the technical solutions of the present invention may be modified or replaced by equivalents 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, 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.

2. The rare earth europium-based zirconate magnetic refrigeration material according to 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 according to claim 2, characterized in that: Includes at least one of the following features: A. When the temperature is 4.5K and the magnetic field changes from 0 to 1T, the maximum magnetic entropy change of the rare earth europium-based zirconate magnetic refrigeration material is ≥3.5J·kg -1 ·K -1 ; B. When the temperature is 4.5K and the magnetic field changes from 0 to 2T, the maximum magnetic entropy change of the rare earth europium-based zirconate magnetic refrigeration material is ≥12.8J·kg -1 ·K -1 .

4. The rare earth europium-based zirconate magnetic refrigeration material according to claim 1, characterized in that: Include 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 2 T, the magnetic refrigeration capacity of the rare earth europium-based zirconate magnetic refrigeration material is ≥44.5 J·kg -1 .

5. The rare earth europium-based zirconate magnetic refrigeration material according to claim 1, characterized in that: The crystal of the rare earth europium-based zirconate magnetic refrigeration material has an orthorhombic crystal system, and its space group is Pbnm.

6. A method for preparing the rare earth europium-based zirconate magnetic refrigeration material according to any one of claims 1 to 5, characterized in that: The steps include: (1) According to the chemical formula (Eu 1-x M x )(Zr 1-y N y ) The stoichiometric ratio of the elements in O3 is Eu2O3, ZrO2, M oxide, and N oxide, and Eu2O3, ZrO2, M oxide, N oxide, and a reducing agent are ball-milled and dried in sequence to obtain a mixed material; the molar ratio of the reducing agent to Eu2O3 is (1.05-1.2):1; (2) heat-treating the mixed material under 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 12 hours.

7. The method for preparing the rare earth europium-based zirconate magnetic refrigeration material according to claim 6, characterized in that: In step (1), the reducing agent includes at least one of coke or graphene.

8. The method for preparing the rare earth europium-based zirconate magnetic refrigeration material according to claim 6, characterized in that: In step (1), the ball milling time is 2-6 hours.

9. The method for preparing the rare earth europium-based zirconate magnetic refrigeration material according to claim 6, wherein: Include at least one of the following EG: E. In step (2), the heat treatment temperature is 1275-1325°C; F. In step (2), the heat treatment time is 12-24h; G. In step (2), the reducing atmosphere is a mixed atmosphere of 0-5% by volume of hydrogen and 95-100% by volume of an inert gas.

10. A magnetic refrigeration device, characterized in that: The rare earth europium-based zirconate magnetic refrigeration material comprises the rare earth europium-based zirconate magnetic refrigeration material according to any one of claims 1 to 5.

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