Magnetic refrigeration single crystal material as well as preparation method and application thereof

Abstract

The invention discloses a magnetic refrigeration single crystal material as well as a preparation method and application thereof, and relates to the technical field of magnetic refrigeration materials. The magnetic refrigeration single crystal material is a triangular lattice borate single crystal, and the chemical formula of the triangular lattice borate single crystal is GdBO3. The magnetic refrigeration single crystal material provided by the invention has higher unit volume and unit mass refrigerating capacity. The GdBO3 single crystal has magnetic ion triangular lattice arrangement, and has a magnetoresistance file effect (the existence of the magnetoresistance file effect can significantly reduce the phase transition temperature), and the effective magnetic cooling temperature zone can extend to 1.8 K or below. The magnetic refrigeration single crystal material provided by the invention has a relatively large magnetocaloric effect (the maximum negative magnetic entropy difference is 57.07 J.kg <-1 >. K <-1 > when the initial state magnetic field is 7T and the final state magnetic field is 0T), and has more excellent heat conduction performance and refrigeration performance compared with a magnetic refrigeration material in a powder form.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic refrigeration materials, and in particular to a magnetic refrigeration single crystal material and a preparation method and application thereof. Background Art

[0002] The magnetocaloric effect refers to the phenomenon that the temperature of a magnetic material changes with a magnetic field. It is mainly divided into two types: magnetocaloric and magnetocaloric. The essence of this phenomenon is that the spin system is affected by the magnetic field and exchanges energy with other systems or the outside world. The magnetocaloric effect of materials can be used for refrigeration in extremely low temperature areas.

[0003] Adiabatic demagnetization refrigeration is a typical method of magnetic refrigeration. The process of producing the refrigeration effect is as follows: the first step is to apply a magnetic field to the material so that the spin is fully polarized to form an ordered state. At this time, the magnetic entropy of the system is extremely low; the second step is to remove the magnetic field, the spins in the material flip in large numbers, and the magnetic entropy increases. This process absorbs heat from the system, thereby cooling the system.

[0004] The magnetic properties of magnetic cooling media determine the size and range of magnetocaloric effect. Trivalent gadolinium-based materials have attracted extensive attention because of their large spin quantum number, corresponding to large magnetic entropy. However, due to the magnetic interaction between its magnetic ions, it enters an ordered state at a higher temperature, that is, its magnetic cooling temperature range is higher.

[0005] Therefore, the prior art still needs to be improved and developed. Summary of the invention

[0006] Based on the above-mentioned deficiencies of the prior art, the object of the present invention is to provide a magnetic refrigeration single crystal material and a preparation method and application thereof, aiming to provide a magnetic refrigeration material with a lower magnetic refrigeration temperature range.

[0007] The technical solution of the present invention is as follows:

[0008] In a first aspect of the present invention, a magnetic refrigeration single crystal material is provided, wherein the magnetic refrigeration single crystal material is a triangular lattice borate single crystal, and the chemical formula of the triangular lattice borate single crystal is GdBO 3 .

[0009] A second aspect of the present invention provides a method for preparing the magnetic refrigeration single crystal material as described above, comprising the following steps:

[0010] Gd 2 O 3 , H 3 BO 3 mixing with a flux to obtain a mixture;

[0011] The magnetic refrigeration single crystal material is obtained by heat treating the mixture at a preset temperature.

[0012] Optionally, the Gd 2 O 3 , H 3 BO 3 The molar ratio to flux is 1:(1-20):(1-25).

[0013] Optionally, the Gd 2 O 3 , H 3 BO 3 The molar ratio to flux is 1:(7-9):(9-11).

[0014] Optionally, the flux includes at least one of alkali metal fluoride, hydrate of alkali metal fluoride, and alkali metal tetrafluoroborate.

[0015] Optionally, the alkali metal fluoride includes at least one of LiF, NaF, KF, RbF, and CsF;

[0016] The alkali metal tetrafluoroborate includes LiBF 4 , NaBF 4 KBF 4 At least one of .

[0017] Optionally, the step of obtaining the magnetic refrigeration single crystal material after heat treating the mixture at a preset temperature specifically includes:

[0018] The mixture is placed in a crucible, and then the crucible containing the mixture is placed in a muffle furnace at 850-1000°C, heated to 950-1100°C at a rate of 50-200°C / h and kept warm for 0.05-48h, then cooled to 700°C at a rate of 1-8°C / h, and then cooled to room temperature at a rate of 10-200°C / h, to obtain the magnetic refrigeration single crystal material in the crucible.

[0019] Optionally, the crucible is a platinum crucible.

[0020] Optionally, the method for preparing the magnetic refrigeration single crystal material further comprises the following steps:

[0021] The crucible containing the magnetic refrigeration single crystal material is placed in a dilute hydrochloric acid aqueous solution, heated to boiling, and kept warm for 5 hours, and then the crucible containing the magnetic refrigeration single crystal material is ultrasonically cleaned to obtain the magnetic refrigeration single crystal material.

[0022] The third aspect of the present invention provides an application of the magnetic refrigeration single crystal material as described above in the present invention and / or the magnetic refrigeration single crystal material prepared by the preparation method as described above in the field of magnetic refrigeration.

[0023] Beneficial effect: The magnetic refrigeration single crystal material provided by the present invention is GdBO 3 The single crystal is an adiabatic demagnetization refrigeration material. Its completely disordered 3-valent gadolinium ion spin system has the largest magnetic entropy Rln(8) J·mol among 4f ions. -1 ·K -1 The transformation process from magnetic order to magnetic disorder of the spin system absorbs heat, thus achieving a cooling effect. The Gd ion density is higher than that of other magnetic cooling materials (such as Gd 3 Ga 5 O 12 and GdLiF 4 ) is higher, therefore, it has a higher cooling capacity per unit volume and per unit mass. 3 The triangular lattice distribution of gadolinium ions in the single crystal results in competitive interactions between adjacent antiferromagnetic moments, which in turn reduces the phase transition temperature (magnetic cooling temperature) and enables magnetic cooling at extremely low temperatures. Specifically, GdBO 3 The single crystal has a triangular lattice arrangement of magnetic ions, has a magnetic frustration effect (the existence of the magnetic frustration effect can significantly reduce the phase transition temperature), and the temperature range of the magnetocaloric effect is lower than that of traditional paramagnetic or antiferromagnetic salts. Its effective magnetic cooling temperature range can extend to below 1.8K. Compared with the current mainstream magnetic cooling materials, the magnetic cooling single crystal material provided by the present invention has a larger magnetocaloric effect (the maximum negative magnetic entropy difference is 57.07 J·kg when the initial magnetic field is 7T and the final magnetic field is 0T). -1 ·K -1 ), which has certain competitiveness in the field of low-temperature magnetic refrigeration. In addition, the magnetic refrigeration single crystal material provided by the present invention has better thermal conductivity and refrigeration performance than the magnetic refrigeration material in powder form (which has poor thermal conductivity and thus leads to poor actual refrigeration effect). BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is the GdBO prepared in Example 1 3 Crystal structure diagram of a single crystal.

[0025] Figure 2 is the GdBO prepared in Example 1 3 Physical picture of single crystal.

[0026] Figure 3 is the GdBO prepared in Example 1 3 XRD pattern of single crystal.

[0027] Figure 4 is the GdBO prepared in Example 1 3 Isothermal magnetization curve of a single crystal.

[0028] Figure 5is the GdBO prepared in Example 1 3 Magnetic entropy difference results of a single crystal under different magnetic fields. DETAILED DESCRIPTION

[0029] The present invention provides a magnetic refrigeration single crystal material and a preparation method and application thereof. To make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0030] Unless otherwise defined, all technical terms and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0031] The embodiment of the present invention provides a magnetic refrigeration single crystal material, wherein the magnetic refrigeration single crystal material is a triangular lattice borate single crystal, and the chemical formula of the triangular lattice borate single crystal is GdBO 3 .

[0032] The magnetic refrigeration single crystal material provided by the present invention is GdBO 3 The single crystal is a material with high-density magnetic ion frustrated crystal, that is, an adiabatic demagnetization refrigeration material. Its completely disordered trivalent gadolinium ion spin system has the largest magnetic entropy Rln(8) J·mol among 4f ions. -1 ·K -1 The transformation process from magnetic order to magnetic disorder of the spin system absorbs heat, thus achieving a cooling effect. The Gd ion density is higher than that of other magnetic cooling materials (such as Gd 3 Ga 5 O 12 and GdLiF 4 ) is higher, therefore, it has a higher cooling capacity per unit volume and per unit mass. 3 The triangular lattice distribution of gadolinium ions in single crystals results in competitive interactions between adjacent antiferromagnetic moments, which in turn reduces the phase transition temperature (magnetic cooling temperature) and enables magnetic cooling at extremely low temperatures. Specifically, GdBO 3 The single crystal has a triangular lattice arrangement of magnetic ions, has a magnetic frustration effect (the existence of the magnetic frustration effect can significantly reduce the phase transition temperature), and the temperature range of the magnetocaloric effect is lower than that of traditional paramagnetic or antiferromagnetic salts. Its effective magnetic cooling temperature range can extend to below 1.8K. Compared with the current mainstream magnetic cooling materials, the magnetic cooling single crystal material provided by the present invention has a larger magnetocaloric effect (the maximum negative magnetic entropy difference is 57.07 J·kg when the initial magnetic field is 7T and the final magnetic field is 0T). -1 ·K -1), which has certain competitiveness in the field of low-temperature magnetic refrigeration. In addition, the magnetic refrigeration single crystal material provided by the present invention has better thermal conductivity and refrigeration performance than the magnetic refrigeration material in powder form (which has poor thermal conductivity, resulting in poor actual refrigeration effect and is difficult to promote to practical application).

[0033] In the embodiment of the present invention, the chemical formula of the triangular lattice borate single crystal is GdBO 3 , the space group is C2 / c, and the unit cell parameters at a temperature of 100K are: α=90°,β=112.842°,γ=90°. That is to say, the chemical formula of the triangular lattice borate single crystal is π-GdBO 3 .

[0034] The embodiment of the present invention further provides a method for preparing the magnetic refrigeration single crystal material as described above, which comprises the following steps:

[0035] S1, Gd 2 O 3 , H 3 BO 3 mixing with a flux to obtain a mixture;

[0036] S2. After heat treatment of the mixture at a preset temperature, the magnetic refrigeration single crystal material is obtained.

[0037] The preparation method provided by the present invention has simple equipment and simple and feasible process. Specifically, Gd 2 O 3 , H 3 BO 3 As raw materials, the flux method is used to grow magnetic refrigeration single crystal material, namely GdBO 3 Single crystal, grown millimeter-scale GdBO 3 The single crystal has smaller thermal stress and is more uniform and complete. At the same time, the magnetocaloric effect of the magnetic refrigeration single crystal material prepared by the preparation method provided by the present invention has a lower temperature range (the effective magnetic refrigeration temperature range can extend to below 1.8K), and has a higher unit volume and unit mass cooling capacity (the maximum negative magnetic entropy difference is 57.07 J·kg when the initial magnetic field is 7T and the final magnetic field is 0T). -1 ·K -1 ).

[0038] In step S1, in some embodiments, the Gd 2 O 3 , H 3 BO 3 The molar ratio of Gd to flux is 1:(1-20):(1-25). 2 O3 , H 3 BO 3 The molar ratio with the flux is 1:1:1, 1:10:1, 1:20:1, 1:1:15, 1:10:15, 1:20:15, 1:1:25, 1:10:25 or 1:20:25, etc. By controlling this ratio, the growth of crystals can be promoted and the "material creeping" phenomenon can be avoided, thereby preparing high-quality materials.

[0039] In some embodiments, the Gd 2 O 3 , H 3 BO 3 The molar ratio of Gd to flux is 1:(7-9):(9-11). 2 O 3 , H 3 BO 3 The molar ratio to flux is 1:7:9, 1:8:9, 1:9:9, 1:7:10, 1:8:10, 1:9:10, 1:7:11, 1:8:11 or 1:9:11, etc.

[0040] In some embodiments, the flux comprises at least one of an alkali metal fluoride, a hydrate of an alkali metal fluoride, and a tetrafluoroborate of an alkali metal. These fluxes are suitable for Gd 2 O 3 The growth of single crystals, in addition, these fluxes can make the raw material Gd 2 O 3 and H 3 BO 3 Melting at a lower temperature can also adjust the target product (Gd 2 O 3 The supersaturated precipitation rate of single crystal) can be adjusted to regulate the crystal growth process.

[0041] In some embodiments, the alkali metal fluoride includes but is not limited to at least one of LiF, NaF, KF, RbF, and CsF.

[0042] In some embodiments, the alkali metal tetrafluoroborate includes but is not limited to LiBF 4 , NaBF 4 KBF 4 At least one of .

[0043] In some embodiments, the flux is a mixture of LiF and NaF, or the flux is a mixture of LiF and KF. If the system has a high viscosity problem when only LiF is used as the flux or if "material creeping" occurs when only LiF is used as the flux, additional NaF (or KF, or KF·2H 2 O) to reduce the viscosity of the system, and also to further avoid the "material creeping" phenomenon and control Gd 2 O 3 With NaF (or KF, or KF·2H 2 O) molar ratio is 1:(1-15), for example, 1:1, 1:5, 1:10 or 1:15, etc.

[0044] In step S2, in some embodiments, the step of obtaining the magnetic refrigeration single crystal material after heat treating the mixture at a preset temperature specifically includes:

[0045] The mixture is placed in a crucible, and then the crucible containing the mixture is placed in a muffle furnace at 850-1000°C (for example, 850°C, 900°C, 950°C or 1000°C, etc.) to heat the raw materials, and then the temperature is increased to 950-1100°C (for example, 950°C, 1000°C, 1050°C or 1100°C) at a rate of 50-200°C / h (for example, 50°C / h, 80°C / h, 100°C / h, 120°C / h, 150°C / h, 180°C / h or 200°C / h, etc.) and kept warm for 0.05-48h (for example, For example, the temperature may be 0.05 h, 1 h, 5 h, 10 h, 15 h, 20 h, 25 h, 30 h, 35 h, 40 h, 45 h or 48 h, etc.), so that the high-temperature melt is fully mixed and uniformly mixed, and then the temperature is reduced to 700 ° C at a rate of 1-8 ° C / h (for example, it can be 1 ° C / h, 1.5 ° C / h, 2 ° C / h, 2.5 ° C / h, 3 ° C / h, 3.5 ° C / h, 4 ° C / h, 4.5 ° C / h, 5 ° C / h, 5.5 ° C / h, 6 ° C / h, 6.5 ° C / h, 7 ° C / h, 7.5 ° C / h or 8 ° C / h, etc.), during which the melt will be supersaturated and precipitated to complete the GdBO 3 The crystal is grown, and then cooled to room temperature at a rate of 10-200°C / h (for example, 10°C / h, 20°C / h, 30°C / h, 50°C / h, 60°C / h, 80°C / h, 100°C / h, 120°C / h, 150°C / h, 180°C / h or 200°C / h, etc.) to obtain the magnetic refrigeration single crystal material in the crucible.

[0046] In some embodiments, the crucible is a platinum crucible, which can avoid GdBO 3 Impurities are generated in the single crystal to obtain pure GdBO 3Single crystal, which makes it have excellent magnetic refrigeration performance.

[0047] In some embodiments, the method for preparing the magnetic refrigeration single crystal material further comprises the following steps:

[0048] The crucible containing the magnetic refrigeration single crystal material is placed in a dilute hydrochloric acid aqueous solution, heated to boiling, and kept warm for 5 hours, and then the crucible containing the magnetic refrigeration single crystal material is ultrasonically cleaned to obtain the magnetic refrigeration single crystal material. The dilute hydrochloric acid aqueous solution can clean the flux on the surface of the crystal, thereby achieving the effect of purification. Ultrasonic cleaning can further reduce impurities on the crystal surface and cause the crystal to fall off.

[0049] An embodiment of the present invention also provides an application of the magnetic refrigeration single crystal material as described above in the field of magnetic refrigeration; or, provides an application of the magnetic refrigeration single crystal material prepared by the preparation method as described above in the field of magnetic refrigeration; or, provides an application of the magnetic refrigeration single crystal material as described above in the present invention and the magnetic refrigeration single crystal material prepared by the preparation method as described above in the field of magnetic refrigeration.

[0050] The magnetic refrigeration single crystal material provided by the present invention is an adiabatic demagnetization refrigeration material with high refrigeration capacity per unit volume and per unit mass. 3 The temperature range of the single crystal magnetocaloric effect is lower than that of traditional paramagnetic or antiferromagnetic salts, and its effective magnetic cooling temperature range can extend to below 1.8K. Compared with the current mainstream magnetic cooling materials, the magnetic cooling single crystal material provided by the present invention has a larger magnetocaloric effect (the maximum negative magnetic entropy difference is 57.07 J·kg when the initial magnetic field is 7T and the final magnetic field is 0T). -1 ·K -1 ) and thermal conductivity, and has excellent magnetic refrigeration performance. Therefore, it can be used in the field of magnetic refrigeration.

[0051] The present invention will be further described below by means of specific examples.

[0052] Example 1

[0053] This embodiment provides a magnetic refrigeration single crystal material (i.e., GdBO 3 A method for preparing a single crystal comprises the following steps:

[0054] Gd 2 O 3 , H 3 BO 3 and LiF in a molar ratio of 1:8:10 to obtain a mixture;

[0055] The mixture was placed in an agate mortar and ground evenly, and then placed in a platinum crucible. The platinum crucible containing the mixture was then placed in a 900°C muffle furnace chamber, heated to 1050°C at a rate of 150°C / h and kept warm for 10h to fully mix the high-temperature melt, and then cooled to 700°C at a rate of 3.5°C / h to complete the GdBO 3 After the crystals grow, they are cooled to room temperature at a rate of 60°C / h. 3 The single crystal is taken out of the platinum crucible.

[0056] Prepare a 10% HCl aqueous solution in a glass beaker and add the GdBO 3 The platinum crucible of the single crystal is immersed in it, heated to boiling, and taken out after keeping warm for 5 hours.

[0057] The GdBO 3 The platinum crucible of the single crystal was placed in an ultrasonic cleaning machine and ultrasonically cleaned for 1 h at room temperature to further clean the impurities on the crystal surface and cause the crystal to fall off, obtaining GdBO 3 Single crystal, its crystal structure is as follows Figure 1 As shown in the figure, the actual picture is as follows Figure 2 shown.

[0058] test:

[0059] (1) GdBO 3 X-ray diffraction test of single crystal

[0060] First, the GdBO obtained in Example 1 3 The single crystal was ground into powder, and the diffraction pattern was measured using a Rigaku SmartLab 9KW model powder X-ray diffractometer (XRD). Figure 3 As shown, the experimental values ​​are basically consistent with the C2 / c space group GdBO 3 The theoretical value is consistent with that of the GdBO prepared in Example 1. 3 The space group of the single crystal is C2 / c, the crystal system is monoclinic, and the unit cell parameters at a temperature of 100K are: α=90°, β=112.842°, γ=90°.

[0061] (2) The following tests were performed using the VSM module of the comprehensive physical property measuring instrument:

[0062] GdBO 3 After the single crystal is lowered to 1.8K, the GdBO 3The single crystal was subjected to a magnetic field parallel (B in-plane) and perpendicular (B out-of-plane) to the triangular lattice layer, and the magnetic field strength was set to 0.2T. The temperature was then raised to 50K at a rate of 4K / min, and the magnetization intensity was recorded. The relationship between the magnetic susceptibility and the inverse of the magnetic susceptibility with temperature was calculated, and a Curie-Weiss fitting analysis was performed. The results show that GdBO 3 The Curie temperatures of the single crystal in two directions are -4.8K and -7.0K, respectively, which indicates that Gd 3+ On the other hand, no antiferromagnetic phase transition was observed above 1.8 K, which indicates that Gd 3+ The triangular lattice structure composed of ions produces a strong frustration effect, and its effective magnetic cooling temperature range can extend to below 1.8K.

[0063] (3) The GdBO obtained in Example 1 was measured at various temperatures using a superconducting quantum interference device (SQUID)-vibrating sample magnetometer of a magnetic measurement system. 3 The single crystal magnetic susceptibility was measured by isothermal field scanning, and the GdBO 3 A single crystal is subjected to magnetic fields parallel (B in-plane) and perpendicular (B out-of-plane) to the triangular lattice layers. The results are as follows Figure 4 As shown. It can be found that at a temperature of 2K, as the magnetic field increases to 7T, the magnetization intensity reaches the theoretical saturation value, indicating that the spin is fully polarized at this moment and reaches a magnetically ordered state. Therefore, removing the magnetic field at a temperature of 2K and a magnetic field of 7T will produce a large magnetocaloric effect.

[0064] In order to measure the specific size of the magnetocaloric effect, GdBO 3 A magnetic field perpendicular to the triangular lattice layer (B out-of-plane) was applied to the single crystal, and the negative magnetic entropy difference under different magnetic fields was calculated. The larger the negative magnetic entropy difference, the stronger the magnetic cooling effect. The results are shown in Figure 5 As shown, B f is the initial magnetic field, B i The maximum negative magnetic entropy difference is 57.07 J·kg when the initial magnetic field is 7 T and the final magnetic field is 0 T. -1 ·K -1 , with a strong magnetocaloric effect.

[0065] Example 2

[0066] This embodiment provides a magnetic refrigeration single crystal material (i.e., GdBO 3 A method for preparing a single crystal comprises the following steps:

[0067] Gd 2 O 3 , H 3 BO3 , LiF, and NaF are mixed in a molar ratio of 1:8:5:5 to obtain a mixture;

[0068] The mixture was placed in an agate mortar and ground evenly, and then placed in a platinum crucible. The platinum crucible containing the mixture was then placed in a 900°C muffle furnace chamber, heated to 1050°C at a rate of 150°C / h and kept warm for 10h to fully mix the high-temperature melt, and then cooled to 700°C at a rate of 3.5°C / h to complete the GdBO 3 After the crystals grow, they are cooled to room temperature at a rate of 60°C / h. 3 The single crystal is taken out of the platinum crucible.

[0069] Prepare a 10% HCl aqueous solution in a glass beaker and add the GdBO 3 The platinum crucible of the single crystal is immersed in it, heated to boiling, and taken out after keeping warm for 5 hours.

[0070] The GdBO 3 The platinum crucible of the single crystal was placed in an ultrasonic cleaning machine and ultrasonically cleaned for 1 h at room temperature to further clean the impurities on the crystal surface and cause the crystal to fall off, obtaining GdBO 3 Single crystal.

[0071] Example 3

[0072] This embodiment provides a magnetic refrigeration single crystal material (i.e., GdBO 3 A method for preparing a single crystal comprises the following steps:

[0073] Gd 2 O 3 , H 3 BO 3 and LiF in a molar ratio of 1:20:25 to obtain a mixture;

[0074] The mixture was placed in an agate mortar and ground evenly, and then placed in a platinum crucible. The platinum crucible containing the mixture was then placed in a 1000°C muffle furnace chamber, heated to 1100°C at a rate of 200°C / h and kept warm for 40h to allow the high-temperature melt to be fully mixed, and then cooled to 700°C at a rate of 8°C / h to complete the GdBO 3 After the crystals grow, they are cooled to room temperature at a rate of 180°C / h. 3 The single crystal is taken out of the platinum crucible.

[0075] Prepare a 10% HCl aqueous solution in a glass beaker and add the GdBO 3The platinum crucible of the single crystal is immersed in it, heated to boiling, and taken out after keeping warm for 5 hours.

[0076] The GdBO 3 The platinum crucible of the single crystal was placed in an ultrasonic cleaning machine and ultrasonically cleaned for 1 h at room temperature to further clean the impurities on the crystal surface and cause the crystal to fall off, obtaining GdBO 3 Single crystal.

[0077] Example 4

[0078] This embodiment provides a magnetic refrigeration single crystal material (i.e., GdBO 3 A method for preparing a single crystal comprises the following steps:

[0079] Gd 2 O 3 , H 3 BO 3 and LiF in a molar ratio of 1:1:1 to obtain a mixture;

[0080] The mixture was ground evenly in an agate mortar and then placed in a platinum crucible. The platinum crucible containing the mixture was then placed in a muffle furnace chamber at 850°C, heated to 950°C at a rate of 50°C / h and kept warm for 5h to allow the high-temperature melt to be fully mixed. The temperature was then lowered to 700°C at a rate of 1°C / h to complete the GdBO 3 After the crystals grow, they are cooled to room temperature at a rate of 10°C / h. 3 The single crystal is taken out of the platinum crucible.

[0081] Prepare a 10% HCl aqueous solution in a glass beaker and add the GdBO 3 The platinum crucible of the single crystal is immersed in it, heated to boiling, and taken out after keeping warm for 5 hours.

[0082] The GdBO 3 The platinum crucible of the single crystal was placed in an ultrasonic cleaning machine and ultrasonically cleaned for 1 h at room temperature to further clean the impurities on the crystal surface and cause the crystal to fall off, obtaining GdBO 3 Single crystal.

[0083] Example 5

[0084] This embodiment provides a magnetic refrigeration single crystal material (i.e., GdBO 3 A method for preparing a single crystal comprises the following steps:

[0085] Gd 2 O 3 , H 3 BO 3 and LiBF 4Mixing in a molar ratio of 1:7:9 to obtain a mixture;

[0086] The mixture was placed in an agate mortar and ground evenly, then placed in a platinum crucible, and then the platinum crucible containing the mixture was placed in a 950°C muffle furnace chamber, heated to 1000°C at a rate of 180°C / h and kept warm for 15h to fully mix the high-temperature melt, and then cooled to 700°C at a rate of 4.5°C / h to complete the GdBO 3 After the crystals grow, they are cooled to room temperature at a rate of 75°C / h. 3 The single crystal is taken out of the platinum crucible.

[0087] Prepare a 10% HCl aqueous solution in a glass beaker and add the GdBO 3 The platinum crucible of the single crystal is immersed in it, heated to boiling, and taken out after keeping warm for 5 hours.

[0088] The GdBO 3 The platinum crucible of the single crystal was placed in an ultrasonic cleaning machine and ultrasonically cleaned for 1 h at room temperature to further clean the impurities on the crystal surface and cause the crystal to fall off, obtaining GdBO 3 Single crystal.

[0089] For GdBO in Examples 2 to 5 3 The single crystal was tested by XRD, the VSM module of the comprehensive physical property measuring instrument was used for testing, the superconducting quantum interference instrument-vibrating sample magnetometer of the magnetic measurement system was used to perform isothermal field scanning magnetic susceptibility measurement at multiple temperatures, and the negative magnetic entropy difference under different magnetic fields was tested. The results obtained were all consistent with those of the GdBO prepared in Example 1. 3 Single crystals are much the same.

[0090] In summary, the present invention provides a magnetic refrigeration single crystal material and a preparation method and application thereof. The magnetic refrigeration single crystal material provided by the present invention is GdBO 3 The single crystal is an adiabatic demagnetization refrigeration material. Its completely disordered 3-valent gadolinium ion spin system has the largest magnetic entropy Rln(8) J·mol among 4f ions. -1 ·K -1 The transformation process from magnetic order to magnetic disorder of the spin system absorbs heat, thus achieving a cooling effect. The Gd ion density is higher than that of other magnetic cooling materials (such as Gd 3 Ga 5 O 12 and GdLiF 4 ) is higher, therefore, it has a higher cooling capacity per unit volume and per unit mass. 3The triangular lattice distribution of gadolinium ions in single crystals results in competitive interactions between adjacent antiferromagnetic moments, which in turn reduces the phase transition temperature (magnetic cooling temperature) and enables magnetic cooling at extremely low temperatures. Specifically, GdBO 3 The single crystal has a triangular lattice arrangement of magnetic ions and has a magnetic frustration effect. The temperature range of the magnetocaloric effect is lower than that of traditional paramagnetic or antiferromagnetic salts, and its effective magnetic cooling temperature range can extend to below 1.8K. Compared with the current mainstream magnetic cooling materials, the magnetic cooling single crystal material provided by the present invention has a larger magnetocaloric effect (the maximum negative magnetic entropy difference is 57.07 J·kg when the initial magnetic field is 7T and the final magnetic field is 0T). -1 ·K -1 ), which has certain competitiveness in the field of low-temperature magnetic refrigeration. In addition, the magnetic refrigeration single crystal material provided by the present invention has better thermal conductivity and refrigeration performance than the magnetic refrigeration material in powder form (which has poor thermal conductivity and thus leads to poor actual refrigeration effect).

[0091] It should be understood that the application of the present invention is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A magnetic refrigeration single crystal material, characterized in that: The magnetic refrigeration single crystal material is a triangular lattice borate single crystal, and the chemical formula of the triangular lattice borate single crystal is GdBO3.

2. A method for preparing the magnetic refrigeration single crystal material according to claim 1, characterized in that: The steps include: Mixing Gd2O3, H3BO3 and flux to obtain a mixture; The magnetic refrigeration single crystal material is obtained by heat treating the mixture at a preset temperature.

3. The preparation method according to claim 2, characterized in that: The molar ratio of Gd2O3, H3BO3 and flux is 1:(1-20):(1-25).

4. The preparation method according to claim 3, characterized in that: The molar ratio of Gd2O3, H3BO3 and flux is 1:(7-9):(9-11).

5. The preparation method according to claim 2, characterized in that: The flux includes at least one of alkali metal fluoride, hydrate of alkali metal fluoride and tetrafluoroborate of alkali metal.

6. The preparation method according to claim 5, characterized in that: The alkali metal fluoride includes at least one of LiF, NaF, KF, RbF, and CsF; The alkali metal tetrafluoroborate includes at least one of LiBF4, NaBF4, and KBF4.

7. The preparation method according to claim 2, characterized in that: The step of obtaining the magnetic refrigeration single crystal material after heat treating the mixture at a preset temperature specifically includes: The mixture is placed in a crucible, and then the crucible containing the mixture is placed in a muffle furnace at 850-1000°C, heated to 950-1100°C at a rate of 50-200°C / h and kept warm for 0.05-48h, then cooled to 700°C at a rate of 1-8°C / h, and then cooled to room temperature at a rate of 10-200°C / h, to obtain the magnetic refrigeration single crystal material in the crucible.

8. The preparation method according to claim 7, characterized in that: The crucible is a platinum crucible.

9. The preparation method according to claim 7, characterized in that: The method for preparing the magnetic refrigeration single crystal material further comprises the following steps: The crucible containing the magnetic refrigeration single crystal material is placed in a dilute hydrochloric acid aqueous solution, heated to boiling, and kept warm for 5 hours, and then the crucible containing the magnetic refrigeration single crystal material is ultrasonically cleaned to obtain the magnetic refrigeration single crystal material.

10. Use of the magnetic refrigeration single crystal material according to claim 1 and / or the magnetic refrigeration single crystal material prepared by the preparation method according to any one of claims 2 to 9 in the field of magnetic refrigeration.

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