A gadolinium borate crystal, its preparation method and application

Abstract

This invention discloses a gadolinium borate crystal, its preparation method, and its applications. The chemical formula of the gadolinium borate crystal is Sr. 14.06 Gd 14.63 (BO3) 24 The gadolinium borate crystal described herein belongs to the orthorhombic crystal system, with space group Pnma and cell parameters α = β = γ = 90°, Z = 2. The gadolinium borate crystal provided by this invention has great potential as a magnetic refrigerant, specifically exhibiting a maximum magnetic entropy change of 42.18 J kg at 2 K and Δμ0H = 7 T. ‑1 K ‑1 Furthermore, this invention also provides a method for preparing the above-mentioned gadolinium borate crystals. This method has mild synthesis conditions, is easy to operate, and has great potential for industrial application.

Description

Technical Field

[0001] This invention relates to the field of magnetic refrigeration materials technology. More specifically, it relates to a gadolinium borate crystal, its preparation method, and its applications. Background Technology

[0002] The selection of magnetic refrigeration materials requires that the magnetic molecules possess a large spin ground state, small magnetic anisotropy, high magnetic density, suitable magnetic exchange, and a low-energy excited spin state. Gd... 3+ The ions possess a large spin ground state (S = 7 / 2), weak exchange coupling, and negligible magnetic anisotropy, thus being rich in Gd. 3+ Gadolinium-based ions can serve as excellent low-temperature magnetic refrigeration materials.

[0003] As early as 1933, Gd₂(SO₄)₃·8H₂O was used as a refrigerant for ultra-low temperatures (below 1K) through adiabatic demagnetization. Gd₃Ga₅O 12 (GGG) and its derivatives Gd3(Ga 1-x Fe x )5O 12 (GGIG) is used as a commercial low-temperature magnetic refrigerant in the 2-20K range. High Gd... 3+ Ion concentration and small anion ligands favor the generation of large magnetic entropy changes (-ΔS). m Therefore, relatively young organic ligands such as formic acid, acetic acid, and oxalic acid, as well as some small inorganic ligands such as [CO3], [OH], [SO4], [PO4], [BO3], and [F], have attracted increasing attention in recent years. Among them, the short ligands [BO3] and [F] may produce a large magnetocaloric effect when combined with gadolinium. Moreover, gadolinium borates have stable physicochemical properties and high thermal conductivity. However, the synthesis of gadolinium borate magnetic refrigeration materials with short ligands reported so far is complex, requiring multiple sintering and cooling processes. In particular, the introduction of the ligand [F] requires additional strict vacuum conditions, and the Gd of such gadolinium borates is also a concern. 3+ The ion concentration also needs to be improved. Summary of the Invention

[0004] Based on the above problems, the main objective of this invention is to provide a novel gadolinium-rich gadolinium-based borate crystal, aiming to achieve superior magnetic refrigeration performance in the field of magnetic refrigeration. Furthermore, another objective of this invention is to provide a method for preparing the aforementioned gadolinium-based borate crystal, which does not require vacuum conditions or a pure gas environment, offers greater controllability, and has lower preparation costs.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a gadolinium borate crystal, wherein the chemical formula of the gadolinium borate crystal is Sr 14.06 Gd 14.63 (BO3) 24 The gadolinium borate crystal belongs to the orthorhombic crystal system, with space group Pnma, and its unit cell parameters are: α=β=γ=90°, Z=2.

[0007] In this invention, Gd 3+ Sr is a magnetic cation. 2+ As an auxiliary cation, low molecular weight BO3 3- A novel gadolinium borate crystal was successfully synthesized using ligands. In constructing the basic crystal framework, Sr, with its relatively small molecular weight, was used. 2+ Cations and ligands BO3 3- Gd is a magnetic cation 3+ Provide as much filling space as possible to increase Gd in the crystal. 3+ The concentration of rare earth elements is adjusted to ensure that there is a certain spacing between magnetic cations to minimize magnetic interactions, thereby increasing the mass ratio of rare earth elements to ligands to improve the magnetic density of the crystal.

[0008] Secondly, the present invention provides a method for preparing the above-mentioned gadolinium borate crystals, the method comprising the following steps:

[0009] The Sr-containing compound, the Gd-containing compound, and their fluxing agent are mixed and heated at a constant rate to 980-1000℃ in an aerobic environment, held at that temperature for 5-6 hours, and then cooled twice to room temperature to obtain the gadolinium borate crystals; wherein the fluxing agent includes a B-containing compound and an F-containing compound.

[0010] Preferably, the Sr-containing compound is selected from SrCO3; the Gd-containing compound is selected from Gd2O3.

[0011] Preferably, the B-containing compound is selected from H3BO3 or B2O3.

[0012] Preferably, the co-solvent is composed of KF·2H2O, K2CO3 and H3BO3.

[0013] Preferably, the molar ratio of KF·2H2O, K2CO3, SrCO3, Gd2O3, and H3BO3 is 3:0.5-1:1:0.5:4.5-5. Furthermore, within the scope of this invention, the raw material ratio can further reduce the proportion of impurity phases in the target product.

[0014] More preferably, the molar ratio of KF·2H2O, K2CO3, SrCO3, Gd2O3 and H3BO3 is 3:0.5:1:0.5:5, wherein raw materials within this ratio range can obtain crystals with larger volumes.

[0015] Preferably, the heating rate of the uniform heating is 30-40℃ / h.

[0016] Preferably, the secondary cooling specifically includes the steps of cooling to 600°C at a cooling rate of 1.5-2°C / h, and then cooling to room temperature at a cooling rate of 20-30°C / h.

[0017] Preferably, the oxygen-rich environment is an air environment.

[0018] Thirdly, the present invention provides an application of the above-mentioned gadolinium borate crystal as a magnetic refrigeration material.

[0019] It is understood that magnetic refrigeration materials containing the above-mentioned gadolinium borate crystals in their raw materials are also within the scope of protection of this invention.

[0020] It should also be noted that, unless otherwise specified, any range described in this invention includes the endpoints, any values ​​between the endpoints, and any subranges formed by the endpoints or any values ​​between the endpoints. Unless otherwise specified, the preparation methods in this invention are conventional methods, and the raw materials used can be obtained from publicly available commercial sources or prepared according to existing technology.

[0021] Beneficial effects of the present invention

[0022] 1) The gadolinium borate crystal provided by this invention exhibits a maximum magnetic entropy change of 42.18 J kg at 2 K and Δμ0H = 7 T. -1 K -1 It has great potential as a magnetic refrigerant.

[0023] 2) The method for preparing gadolinium borate crystals provided by this invention is mild, convenient, quick, and easy to operate, and has great application prospects. Attached Figure Description

[0024] Figure 1 The Sr crystal prepared in Example 1 is shown. 14.06 Gd 14.63 (BO3) 24 XRD pattern.

[0025] Figure 2 The Sr crystal prepared in Example 1 is shown. 14.06 Gd 14.63 (BO3) 24 A structural diagram.

[0026] Figure 3 The Sr crystal prepared in Example 1 is shown. 14.06 Gd 14.63 (BO3) 24 The infrared spectrum.

[0027] Figure 4 The Sr crystal prepared in Example 1 is shown. 14.06 Gd 14.63 (BO3) 24 Thermogravimetric curve.

[0028] Figure 5 The Sr crystal prepared in Example 1 is shown. 14.06 Gd 14.63 (BO3) 24 The variable-temperature magnetic susceptibility curve and the Curie-Weiss fitting curve.

[0029] Figure 6 The Sr crystal prepared in Example 1 is shown. 14.06 Gd 14.63 (BO3) 24 The temperature- and field-varying magnetization intensity diagram.

[0030] Figure 7 The Sr crystal prepared in Example 1 is shown. 14.06 Gd 14.63 (BO3) 24 The graph shows the change in magnetic entropy. Detailed Implementation

[0031] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments, further clarifies the invention. It should be understood that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0032] Example 1

[0033] Sr grown using a co-solvent method 14.06 Gd 14.63 (BO3) 24 Crystal formation includes the following steps:

[0034] The raw materials KF·2H2O, K2CO3, SrCO3, Gd2O3, and H3BO3 were accurately weighed in a molar ratio of 3:0.5:1:0.5:5 and ground uniformly. The mixture was then placed into an open platinum crucible with a diameter of 20mm × 20mm and compacted. Under air conditions, the temperature was uniformly increased to 1000℃ at a rate of 40℃ / h and held at this temperature for 5 hours to ensure homogeneous mixing of the melt. The temperature was then lowered to 600℃ at a rate of 2℃ / h, and then rapidly reduced to room temperature at a rate of 20℃ / h. The resulting colorless, blocky single crystal is SrCO3. 14.06 Gd 14.63 (BO3) 24 .

[0035] The Sr prepared in this example 14.06 Gd 14.63 (BO3) 24 The crystal samples were subjected to the following tests:

[0036] Structural characterization:

[0037] XRD was used to analyze the Sr obtained in this example. 14.06 Gd 14.63 (BO3) 24 The crystal was characterized, and the results are as follows: Figure 1 As shown in the figure, Sr 14.06 Gd 14.63 (BO3) 24 It belongs to the orthorhombic crystal system, with space group Pnma, and its unit cell parameters are: α=β=γ=90°, Z=2.

[0038] The Sr obtained in this example 14.06 Gd 14.63 (BO3) 24 See structural diagram Figure 2 As shown.

[0039] Figure 3 The Sr obtained in this example 14.06 Gd 14.63 (BO3) 24 The results of the crystal infrared spectroscopy characterization, as shown in the figure, indicate that BO3 3- The asymmetric stretching vibration peaks are at 1369, 1252, and 1203 cm⁻¹. -1 BO3 3- The symmetrical stretching vibration peak is at 939 cm⁻¹ -1 BO3 3- The bending vibration peaks are located at 737 and 615 cm. -1 Infrared spectroscopy indicates that Sr 14.06 Gd 14.63 (BO3) 24The coordination mode of B in the crystal is BO3, which matches the actual structure.

[0040] Thermal stability test:

[0041] The Sr 14.06 Gd 14.63 (BO3) 24 Thermogravimetric analysis results of the crystal are as follows Figure 4 As shown, this indicates that the crystalline material exhibits good stability within a temperature range of room temperature to 1150℃, with no phase transition or mass loss.

[0042] Magnetic test:

[0043] The following magnetocaloric effects were studied using the Quantum Design PPMS-9 integrated property system within the range of 2K-300K and under magnetic field conditions of 0T-7T:

[0044] Sr was measured under conditions of temperature range of 2K-300K and magnetic field range of 0-7T. 14.06 Gd 14.63 (BO3) 24 The temperature-dependent magnetic susceptibility and its reciprocal curves for the crystal are shown below. Figure 5 As shown. Based on the Curie-Weiss theorem, linear fitting of the reciprocal curve of the variable-temperature magnetic susceptibility indicates that the compound is a paramagnetic salt material with a Curie constant C = 7.51 emu K mol. -1 The Werghiz constant θ = -0.58K, a positive Werghiz constant indicates that Sr 14.06 Gd 14.63 (BO3) 24 The extremely weak antiferromagnetic coupling of crystals makes them suitable for use as magnetic refrigeration materials.

[0045] Sr was measured under conditions of a temperature range of 2K-10K and a magnetic field range of 0-7T. 14.06 Gd 14.63 (BO3) 24 Temperature- and field-varying magnetization diagrams of crystals, such as... Figure 6 As shown in the figure. The curve shows that as the magnetic field strength increases, Sr 14.06 Gd 14.63 (BO3) 24 The magnetization of the crystal gradually increases and reaches a saturation value of 6.46 Nμ at a temperature of 2 K and a magnetic field of 7 T. Β And the theoretical value 7Nμ Β Very close.

[0046] Sr 14.06 Gd 14.63 (BO3) 24The change in magnetic entropy of a crystal can be estimated using Maxwell's formula: it can be estimated using magnetization data under varying temperature and field conditions, as shown in the figure. Figure 7 The magnetic entropy curve shows that the crystalline material exhibits a maximum magnetic entropy change of 42.18 J kg at 2 K and Δμ0H = 7 T within the test range. -1 K -1 .

[0047] Example 2

[0048] Sr grown using a co-solvent method 14.06 Gd 14.63 (BO3) 24 Crystal formation includes the following steps:

[0049] The raw materials KF·2H₂O, K₂CO₃, SrCO₃, Gd₂O₃, and H₃BO₃ were accurately weighed in a molar ratio of 3:1:1:0.5:5 and ground uniformly. The mixture was then placed into an open platinum crucible with a diameter of 20mm × 20mm and compacted. Under an oxygen-rich environment, the temperature was uniformly raised to 1000℃ and held for 5 hours to ensure homogeneous mixing of the melt. The temperature was then lowered to 600℃ at a rate of 2℃ / h, followed by a rapid cooling to room temperature at a rate of 20℃ / h. The resulting colorless, blocky single crystal is SrCO₃. 14.06 Gd 14.63 (BO3) 24 .

[0050] XRD was used to analyze the Sr obtained in this example. 14.06 Gd 14.63 (BO3) 24 The crystals were characterized, and the results were basically consistent with those of Example 1.

[0051] Example 3

[0052] Sr grown using a co-solvent method 14.06 Gd 14.63 (BO3) 24 Crystal formation includes the following steps:

[0053] The raw materials KF·2H₂O, K₂CO₃, SrCO₃, Gd₂O₃, and B₂O₃ were accurately weighed in a molar ratio of 3:0.5:1:0.5:2.5 and ground uniformly. The mixture was then placed into an open platinum crucible with a diameter of 20mm × 20mm and compacted. Under an oxygen-rich environment, the temperature was uniformly raised to 1000℃ and held for 5 hours to ensure homogeneous mixing of the melt. The temperature was then lowered to 600℃ at a rate of 2℃ / h, followed by a rapid cooling to room temperature at a rate of 20℃ / h. The resulting colorless, blocky single crystal is SrCO₃. 14.06 Gd 14.63 (BO3) 24 .

[0054] XRD was used to analyze the Sr obtained in this example. 14.06 Gd 14.63 (BO3) 24 The crystals were characterized, and the results were basically consistent with those of Example 1.

[0055] Example 4

[0056] Sr grown using a co-solvent method 14.06 Gd 14.63 (BO3) 24 Crystal formation includes the following steps:

[0057] The raw materials KF·2H2O, K2CO3, SrCO3, Gd2O3, and H3BO3 were accurately weighed in a molar ratio of 3:0.5:1:0.5:5 and ground uniformly. The mixture was then placed into an open platinum crucible with a diameter of 20mm × 20mm and compacted. Under an oxygen-rich environment, the temperature was uniformly raised to 980℃ and held for 6 hours to ensure homogeneous mixing of the melt. The temperature was then lowered to 600℃ at a rate of 2℃ / h, and then rapidly reduced to room temperature at a rate of 20℃ / h. The resulting colorless, blocky single crystal is SrCO3. 14.06 Gd 14.63 (BO3) 24 .

[0058] XRD was used to analyze the Sr obtained in this example. 14.06 Gd 14.63 (BO3) 24 The characterization results were basically consistent with those of Example 1.

[0059] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A gadolinium borate crystal, characterized in that, The chemical formula of the gadolinium borate crystal is Sr 14.06 Gd 14.63 (BO3) 24 The gadolinium borate crystals described belong to the orthorhombic crystal system, with space group [missing information]. Pnma Its cell parameters are: a = 22.3153(5)Å, b = 15.9087(4)Å, c = 8.7507(2)Å, α = β = γ = 90°, Z = 2.

2. A method for preparing gadolinium borate crystals as described in claim 1, characterized in that, Includes the following steps: The Sr-containing compound, the Gd-containing compound, and their fluxing agent are mixed and heated at a constant rate to 980-1000℃ in an aerobic environment, held at that temperature for 5-6 hours, and then cooled twice to room temperature to obtain the gadolinium borate crystals; wherein the fluxing agent includes a B-containing compound and an F-containing compound.

3. The preparation method according to claim 2, characterized in that, The Sr-containing compound is selected from SrCO3; the Gd-containing compound is selected from Gd2O3.

4. The preparation method according to claim 2, characterized in that, The B-containing compound is selected from H3BO3 or B2O3.

5. The preparation method according to claim 3, characterized in that, The co-solvent is composed of KF·2H2O, K2CO3 and H3BO3.

6. The preparation method according to claim 5, characterized in that, The molar ratio of KF·2H2O, K2CO3, SrCO3, Gd2O3 and H3BO3 is 3: 0.5-1: 1: 0.5: 4.5-5.

7. The preparation method according to claim 5, characterized in that, The molar ratio of KF·2H2O, K2CO3, SrCO3, Gd2O3 and H3BO3 is 3: 0.5: 1: 0.5:

5.

8. The preparation method according to claim 2, characterized in that, The uniform heating rate is 30-40℃ / h.

9. The preparation method according to claim 2, characterized in that, The secondary cooling specifically includes the steps of reducing the temperature to 600°C at a cooling rate of 1.5-2°C / h, and then reducing it to room temperature at a cooling rate of 20-30°C / h.

10. The application of a gadolinium borate crystal as described in claim 1 or a gadolinium borate crystal obtained by any of the preparation methods described in claims 2-9 in the field of magnetic refrigeration.

11. A magnetic refrigeration material, characterized in that, Its main raw material is the gadolinium borate crystal as described in claim 1 or the gadolinium borate crystal obtained by any of the preparation methods described in claims 2-9.

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