Rare earth-based titanate polycrystalline material of two-dimensional triangular lattice, preparation method and application thereof

Abstract

This invention provides a two-dimensional triangular lattice rare-earth-based titanate polycrystalline material, its preparation method, and its applications. The chemical formula of the rare-earth-based titanate polycrystalline material is Ba6M2Ti4O. 17 The space group is P63 / mmc, where M is one or more of Nd, Gd, and Yb. The novel two-dimensional triangular lattice rare-earth-based titanate polycrystalline material provided by this invention has a compact structure, a simple preparation process, and its frustrated structure of localized electron spins significantly reduces the minimum cooling temperature to the tens of millikons. Furthermore, it exhibits high magnetic ion density and large cooling capacity, making it an excellent magnetic refrigerant.

Description

Technical Field

[0001] This invention belongs to the field of magnetic refrigeration technology. Specifically, this invention relates to a rare-earth-based titanate polycrystalline magnetic refrigeration material with a two-dimensional triangular lattice structure, its preparation method, and its application. Background Technology

[0002] Ultra-low temperature technology, referring to temperatures below 1 Kelvin, is a crucial cornerstone for cutting-edge scientific exploration and technological development. In basic science, it is an important tool for discovering and studying new states of matter and quantum phenomena such as topological superconductivity and the fractional quantum Hall effect. At the strategic application level, this technology is indispensable for maintaining the extremely high sensitivity of deep space exploration devices such as X-ray microcalorimeters, and for ensuring the coherence time of core quantum devices such as superconducting qubits and quantum memories.

[0003] Currently, mainstream cryogenic refrigeration technology relies on helium-3 to helium-4 dilution refrigeration. However, this technology has a huge demand for helium-3 isotopes, while my country's helium-3 production capacity is severely insufficient, making it almost entirely dependent on imports. This "helium resource bottleneck" has become a core obstacle restricting the independent control and large-scale development of cryogenic equipment in my country.

[0004] To overcome the aforementioned resource bottlenecks, adiabatic demagnetization refrigeration (ADR) technology based on the magnetocaloric effect is considered a key alternative. This technology achieves cooling through a magnetization-demagnetization process, does not rely on scarce helium-3 resources, and has broad development prospects.

[0005] However, the traditional paramagnetic salt working fluids (such as CrK(SO4)2·12H2O, (NH4)2Mn(SO4)2·6H2O, etc.) used in this technology have significant performance shortcomings and are difficult to meet the needs of modern applications. Traditional paramagnetic salt working fluids utilize magnetic fields to achieve spin ordering, and then demagnetize under adiabatic conditions, using the spin system to absorb lattice entropy to achieve cooling. However, due to the low magnetic ion density of traditional paramagnetic salt working fluids, the magnetic entropy change (cooling capacity) is small, resulting in insufficient cooling capacity, which cannot meet the stringent requirements of quantum chips (operating at the tens of millikr level) or space exploration (requiring continuous milliwatt-level cooling capacity). In addition, the dehydration of hydrated paramagnetic salts under high vacuum conditions leads to problems such as low heat exchange efficiency, poor reliability, and even failure, which also causes many risks and difficulties in practical use, limiting the popularization of related applications.

[0006] To address the shortcomings of traditional working fluids, domestic research institutions are actively exploring novel magnetic refrigeration materials. For example, many quantum frustrated magnetic materials have recently been considered as candidates for refrigeration working fluids due to their stable properties. However, the lowest achievable cooling temperature of existing quantum frustrated magnetic materials is limited, still failing to meet the stringent requirements of quantum chips or space exploration, and they also suffer from problems such as relatively small cooling capacity.

[0007] CN120496982A discloses a rare earth aluminate low-temperature magnetic refrigeration material. Although its magnetic entropy change is relatively large, its operating temperature range is relatively high, above 2K, which is far from meeting the requirements of ultra-low temperature technology, and the preparation process is complex.

[0008] CN119811811A discloses a gadolinium molybdate low-temperature magnetic refrigeration material. Although its preparation process is relatively simple and its refrigeration temperature can reach below 2K, its minimum refrigeration temperature is limited to no less than 400 mK, and it is difficult to reach the extremely low temperature refrigeration temperature of about 100 mK or even 10 mK.

[0009] Therefore, the field of cryogenic refrigeration urgently needs a novel magnetic refrigeration material with lower cooling temperatures, larger cooling capacity, higher stability, and simpler preparation processes. Developing such a novel magnetic refrigeration material is key to overcoming existing technological bottlenecks and promoting the independent control and large-scale application of cryogenic equipment in my country. Summary of the Invention

[0010] To address the above problems, the purpose of this invention is to provide a novel two-dimensional triangular lattice rare-earth-based titanate polycrystalline material with a compact structure, simple preparation process, and a frustrated structure of localized electron spin that greatly reduces the minimum cooling temperature, even reaching the level of ten milliks. It also has a high magnetic ion density and a large cooling capacity, making it an excellent magnetic refrigerant.

[0011] The above-mentioned objective of the present invention is achieved by providing the following technical solution:

[0012] In a first aspect, the present invention provides a two-dimensional triangular lattice rare-earth-based titanate polycrystalline material with the chemical formula Ba6M2Ti4O. 17 The space group is P63 / mmc, where M is one or more of Nd, Gd and Yb.

[0013] The rare earth-based two-dimensional triangular lattice Ba6M2Ti4O provided by this invention 17 The material preparation process is simple and the raw materials are inexpensive. The preparation cycle is short and the structure is compact. In actual measurement, the lowest temperature that can be reached is 25 mK.

[0014] According to the rare earth-based titanate polycrystalline material provided by the present invention, M is Nd, and the lattice constant of the material is a=b=5.99 Å and c=29.93 Å.

[0015] According to the rare earth-based titanate polycrystalline material provided by the present invention, M is Gd, and the lattice constant of the material is a=b=5.96 Å and c=29.70 Å.

[0016] According to the rare earth-based titanate polycrystalline material provided by the present invention, M is Yb, and the lattice constant of the material is a=b=5.90 Å and c=29.40 Å.

[0017] Figure 1 This is the rare-earth-based titanate polycrystalline material Ba6M2Ti4O with a two-dimensional triangular lattice structure provided by the present invention. 17 The crystal structure of (M=Nd, Gd, Yb), where yellow atoms represent Ti. 4+ Ions, pink indicates Ba 2+ Ions, blue indicates magnetic ions M 3+ Red indicates O 2- ion.

[0018] Figure 2 The magnetic ion M in the rare earth-based titanate polycrystalline material with a two-dimensional triangular lattice structure provided according to the present invention is shown. 3+ In the triangular structure formed on the two-dimensional plane, for M to be Nd, Gd and Yb, the nearest magnetic ion spacings are d0 = 5.993 Å, 5.960 Å and 5.904 Å, respectively, and their interlayer distances are d1 = 7.398 Å, 7.342 Å and 7.266 Å, and d2 = 7.567 Å, ​​7.509 Å and 7.432 Å, respectively.

[0019] According to the rare-earth-based titanate polycrystalline material provided by the present invention, M is Nd, and the rare-earth-based titanate polycrystalline material has an Outer Sigmund temperature of approximately -0.051 K in the range of 0.4 K to 1.2 K, and an effective magnetic moment of 1.53 μm. B .

[0020] The rare-earth-based titanate polycrystalline material provided by the present invention, wherein M is Gd, has an Outer Si temperature of approximately -0.487 K in the range of 0.46 K to 1.33 K, and an effective magnetic moment of 6.01 μm. B .

[0021] According to the rare-earth-based titanate polycrystalline material provided by the present invention, M is Yb, and the rare-earth-based titanate polycrystalline material has an Outer Sigmund temperature of approximately -0.033 K in the range of 0.4 K to 1.66 K, and an effective magnetic moment of 1.69 μm. B .

[0022] According to the rare-earth-based titanate polycrystalline material provided by the present invention, wherein M is Nd, and at a temperature of 0-2 K, the maximum magnetic entropy change of the rare-earth-based titanate polycrystalline material controlled by a magnetic field is -ΔS≤11.53 J / (mol·K), and the volume magnetic entropy density is 41.1 mJ / (cm). 3 ·K), magnetic ion density is 4.30 nm -3 .

[0023] According to the rare-earth-based titanate polycrystalline material provided by the present invention, wherein M is Gd, and at a temperature of 0-2 K, the maximum magnetic entropy change of the rare-earth-based titanate polycrystalline material controlled by a magnetic field is -ΔS≤34.58 J / (mol·K), and the volume magnetic entropy density is 126 mJ / (cm). 3 ·K), magnetic ion density is 4.38 nm -3 .

[0024] According to the rare-earth-based titanate polycrystalline material provided by the present invention, wherein M is Yb, and at a temperature of 0-2 K, the maximum magnetic entropy change of the rare-earth-based titanate polycrystalline material controlled by a magnetic field is -ΔS≤11.53 J / (mol·K), and the volume magnetic entropy density is 40.3 mJ / (cm). 3 ·K), magnetic ion density is 4.50 nm -3 .

[0025] According to the rare earth-based titanate polycrystalline material provided by the present invention, wherein M is Nd, and the material is demagnetized from an initial magnetic field of 9 T at an initial temperature of 4 K or less, preferably 2 K or less, and the temperature of the rare earth-based titanate polycrystalline material reaches 42 mK when the magnetic field drops to zero.

[0026] According to the rare earth-based titanate polycrystalline material provided by the present invention, wherein M is Gd, and the material is demagnetized from an initial magnetic field of 6 T at an initial temperature of 4 K or less, preferably 2 K or less, and the temperature of the rare earth-based titanate polycrystalline material reaches 126 mK when the magnetic field drops to zero.

[0027] According to the rare earth-based titanate polycrystalline material provided by the present invention, wherein M is Yb, and the rare earth-based titanate polycrystalline material is demagnetized from an initial magnetic field of 6 T at an initial temperature of 4 K or less, preferably 2 K or less, and the temperature of the rare earth-based titanate polycrystalline material reaches 25 mK when the magnetic field drops to zero.

[0028] In a second aspect, the present invention provides a method for preparing a two-dimensional triangular lattice rare-earth-based titanate polycrystalline material according to the first aspect of the present invention, which includes the following steps:

[0029] S1. Mix BaCO3, TiO2 and M2O3 according to the stoichiometric ratio, then preheat to 600-900℃ and maintain for 0-10 hours to obtain a preheated mixture;

[0030] S2. The mixture obtained in step S1, which has been preheated, is heated again to 1000-1600°C and sintered at this temperature for at least 48 hours. After cooling to room temperature, it is then ground and compressed into tablets.

[0031] S3. Repeat the preliminary heating and secondary heating steps at least once, and grind to obtain the rare earth-based titanate polycrystalline material.

[0032] According to the preparation method provided by the present invention, the initial heating temperature is 800-900℃.

[0033] According to the preparation method provided by the present invention, the secondary heating temperature is 1200-1500℃.

[0034] According to the preparation method provided by the present invention, the sintering time is 48-96 hours.

[0035] According to the preparation method provided by the present invention, the repeating step in step S3 is performed once.

[0036] Thirdly, the present invention provides the application of the two-dimensional triangular lattice rare earth-based titanate polycrystalline material described in the first aspect of the present invention or the two-dimensional triangular lattice rare earth-based titanate polycrystalline material prepared by the preparation method described in the second aspect of the present invention as an adiabatic and demagnetizing refrigerant.

[0037] The present invention has at least the following beneficial technical effects:

[0038] (1) Excellent extreme cooling performance: It can achieve extremely low temperature cooling, and the lowest temperature during the adiabatic demagnetization process can reach 25 mK, which can cover the extremely low temperature range of hundreds of millikans or even tens of millikans. This is because the local electron spin frustration structure of the two-dimensional triangular lattice rare earth-based titanate polycrystalline material of the present invention greatly reduces the cooling temperature.

[0039] (2) Strong cooling capacity: It has a high magnetic ion density and magnetic entropy density, which makes its cooling capacity greater and its cooling efficiency higher.

[0040] (3) High material stability: The material itself is stable, overcoming the defects of unstable chemical properties of traditional hydrated paramagnetic salts, making it more reliable in practical applications.

[0041] (4) Economic advantages of the preparation process: The preparation process is simple, the raw materials are inexpensive, and the preparation cycle is short, making it very suitable for large-scale industrial production and application.

[0042] (5) Scientific design of structure: Its two-dimensional triangular lattice structure and localized electron spin frustration structure are the key to achieving extremely low cooling temperature, scientifically balancing low temperature performance and material stability.

[0043] The two-dimensional triangular lattice material provided by this invention successfully solves the defects of traditional paramagnetic salts (unstable and complex process) and existing quantum frustration materials (limited cooling temperature and small cooling capacity). It is an excellent magnetic refrigerant that integrates excellent low-temperature performance, high stability and good industrialization prospects, which will strongly promote the development of adiabatic demagnetization refrigeration technology in my country. Attached Figure Description

[0044] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings, wherein:

[0045] Figure 1 This illustrates a quantum frustration magnet, Ba6M2Ti4O, with a two-dimensional triangular lattice structure according to the present invention. 17 (M = Nd, Gd, Yb) Crystal structure, yellow atoms represent Ti 4+ Ions, pink indicates Ba 2+ Ions, blue indicates magnetic ions M 3+ Red indicates O 2- ion;

[0046] Figure 2 Display magnetic ion M 3+ For the triangular structures formed on the two-dimensional plane, the magnetic ion spacings for M being Nd, Gd, and Yb are d0 = 5.993 Å, 5.960 Å, and 5.904 Å, respectively.

[0047] Figure 3 The Ba6Nd2Ti4O prepared according to Examples 1-3 is shown. 17 Ba6Gd2Ti4O 17 and Ba6Yb2Ti4O 17 X-ray diffraction patterns of polycrystalline materials;

[0048] Figure 4 The Ba6Nd2Ti4O prepared according to Example 1 is shown. 17 The magnetic susceptibility-temperature curves and the reciprocal of magnetic susceptibility-temperature curves of the polycrystalline material in the range of 0.4K–2.0K are shown. The Curie-Weiss fit for the range of 0.4K–1.2K yields a Weiss temperature of -0.051K and an effective magnetic moment of 1.53 μm. B ;

[0049] Figure 5 The Ba6Gd2Ti4O prepared according to Example 2 is shown. 17 The magnetic susceptibility-temperature curves and the reciprocal of magnetic susceptibility-temperature curves of the polycrystalline material in the range of 0.4K–2.0K are shown. Curie-Weiss fitting is performed for the range of 0.46K–1.33K, with a Weiss temperature of -0.487K and an effective magnetic moment of 6.01 μm. B ;

[0050] Figure 6The Ba6Yb2Ti4O prepared according to Example 3 is shown. 17 The magnetic susceptibility-temperature curves and the reciprocal of magnetic susceptibility-temperature curves of the polycrystalline material in the range of 0.4K–2.0K are shown. The Curie-Weiss fit for the range of 0.4K–1.66K yields a Weiss temperature of -0.033K and an effective magnetic moment of 1.69 μK. B ;

[0051] Figure 7 Showing Ba6Nd2Ti4O 17 Isothermal magnetization curves at different temperatures;

[0052] Figure 8 Display Ba6Gd2Ti4O 17 Isothermal magnetization curves at different temperatures;

[0053] Figure 9 Display Ba6Yb2Ti4O 17 Isothermal magnetization curves at different temperatures;

[0054] Figure 10 Showing Ba6Nd2Ti4O 17 Refrigeration curves under different initial conditions;

[0055] Figure 11 Display Ba6Gd2Ti4O 17 Refrigeration curves under different initial conditions;

[0056] Figure 12 Display Ba6Yb2Ti4O 17 Refrigeration curves under different initial conditions. Detailed Implementation

[0057] The present invention will be further described in detail below with reference to specific embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0058] Example 1: Rare Earth-based Two-Dimensional Triangular Lattice Material Ba6Nd2Ti4O 17 Preparation

[0059] Using BaCO3, TiO2, and Nd2O3 as raw materials, they were uniformly ground and mixed in a stoichiometric ratio of 6:4:1, and then transferred to a quartz crucible. The mixture was first heated from room temperature to 900℃ and held for 5 hours, then heated to 1300℃ and sintered at this temperature for 96 hours. After cooling to room temperature, the mixture was thoroughly ground and then pressed into tablets using a tablet press. The tablets were then transferred back to the quartz crucible, and the heating and sintering process was repeated once more. The mixture was then ground again to obtain the two-dimensional triangular lattice material Ba6Nd2Ti4O. 17 Pure phase powder.

[0060] Example 2: Rare Earth-based Two-Dimensional Triangular Lattice Material Ba6Gd2Ti4O 17 Preparation

[0061] Using BaCO3, TiO2, and Gd2O3 as raw materials, they were uniformly ground and mixed in a stoichiometric ratio of 6:4:1, and then transferred to a quartz crucible. The mixture was first heated from room temperature to 900℃ and held for 5 hours, then heated to 1300℃ and sintered at this temperature for 96 hours. After cooling to room temperature, the mixture was thoroughly ground and then pressed into tablets using a tablet press. The tablets were then transferred back to the quartz crucible, and the heating and sintering process was repeated once more. The mixture was then ground again to obtain the two-dimensional triangular lattice material Ba6Gd2Ti4O. 17 Pure phase powder.

[0062] Example 3: Rare Earth-based Two-Dimensional Triangular Lattice Material Ba6Yb2Ti4O 17 Preparation

[0063] Using BaCO3, TiO2, and Yb2O3 as raw materials, they were uniformly ground and mixed in a stoichiometric ratio of 6:4:1, and then transferred to a quartz crucible. The mixture was first heated from room temperature to 900℃ and held for 5 hours, then heated to 1400℃ and sintered at this temperature for 96 hours. After cooling to room temperature, the mixture was thoroughly ground and then pressed into tablets using a tablet press. The tablets were then transferred back to the quartz crucible, and the heating and sintering process was repeated once more. The mixture was then ground again to obtain the two-dimensional triangular lattice material Ba6Yb2Ti4O. 17 Pure phase powder.

[0064] Figure 3 Ba6Nd2Ti4O prepared according to Examples 1-3 17 Ba6Gd2Ti4O 17 and Ba6Yb2Ti4O 17 X-ray diffraction pattern of polycrystalline materials. As shown in the figure, this invention successfully prepared the two-dimensional triangular lattice material Ba6Nd2Ti4O. 17 Ba6Gd2Ti4O 17 and Ba6Yb2Ti4O 17 Material.

[0065] Example 4 Characterization of Magnetic Properties

[0066] The two-dimensional triangular lattice materials Ba6Nd2Ti4O prepared in Examples 1-3 were analyzed using the commercially available Quantum Design Physical Property Measurement System (PPMS). 17 Ba6Gd2Ti4O 17 and Ba6Yb2Ti4O 17The magnetic properties of the material are characterized, including magnetic susceptibility, magnetization data, and magnetization-magnetic field variation data, as follows: Figures 4-9 As shown.

[0067] Figure 4-6 The two-dimensional triangular lattice material Ba6Nd2Ti4O prepared in Examples 1-3 17 Ba6Gd2Ti4O 17 and Ba6Yb2Ti4O 17 The magnetic susceptibility-temperature curves and the reciprocal of magnetic susceptibility-temperature curves of the materials are presented. These materials satisfy Curiewes' law at low temperatures and exhibit Curiewes behavior below 2 K. Magnetic Nd ions can be obtained by Curiewes fitting in the linear regions of 0.4 K–1.2 K, 0.46 K–1.33 K, and 0.4 K–1.66 K. 3+ Gd 3+ Yb 3+ The outer temperatures are approximately -0.051 K, -0.487 K, and -0.033 K, respectively, indicating relatively low interaction strengths, making them suitable for cryogenic magnetic refrigeration. The effective magnetic moments are 1.53 μm. B 6.01μ B 1.69 μ B Nd 3+ Yb 3+ After spin-orbit coupling, the ion is influenced by the crystal field, resulting in a dual ground state. At low temperatures, it exhibits an effective spin of -1 / 2 and weak antiferromagnetic interaction. The fitted effective magnetic moments at low temperatures are 1.53 μm. B and 1.69 μ B Gd 3+ The ion has a total orbital angular momentum of 0, is unaffected by the crystal field, has an effective spin of 7 / 2, and exhibits weak antiferromagnetic interaction. At low temperatures, its fitted effective magnetic moment is 6.01 μm. B .

[0068] The two-dimensional triangular lattice material Ba6Nd2Ti4O prepared in Examples 1-3 17 Ba6Gd2Ti4O 17 and Ba6Yb2Ti4O 17 The magnetization-magnetic field variation data of the material were tested, such as... Figure 7-9 As shown, the magnetization intensity increases with the increase of the external magnetic field, and the magnetic moment of a magnetic field of 7 T and above reaches saturation.

[0069] The two-dimensional triangular lattice material Ba6Nd2Ti4O prepared in Examples 1-3 17 Ba6Gd2Ti4O 17 and Ba6Yb2Ti4O 17The low-temperature magnetic refrigeration properties of the material were analyzed.

[0070] Based on the magnetic entropy theory of statistical mechanics, the molar magnetic entropy S of a material in a perfectly paramagnetic state is... M It can be described by the following formula:

[0071] S M =NRln(2J+1),

[0072] Where R = 8.314 J / (mol·K), which is the universal gas constant, N is the number of magnetic ions contained in the chemical unit cell of the material, and J is the effective total angular momentum quantum number of the magnetic ions (which manifests as effective spin under the influence of a low-temperature crystal field). This formula is used to calculate the maximum achievable magnetic entropy change of the material.

[0073] For Ba6Nd2Ti4O 17 Ba6Gd2Ti4O 17 and Ba6Yb2Ti4O 17 All three materials have N=2 magnetic ions in each chemical formula unit, with Nd ions being the most abundant. 3 +、Gd 3+ and Yb 3+ The effective total angular momentum quantum number J is 1 / 2 (Nd 3+ ), 7 / 2 (Gd 3 + ) and 1 / 2 (Yb 3+ ). Calculations show that Ba6Nd2Ti4O 17 Ba6Gd2Ti4O 17 and Ba6Yb2Ti4O 17 At temperatures below 2 K, the three materials can achieve maximum magnetic entropy changes of 11.53 J / (mol·K), 34.58 J / (mol·K), and 11.53 J / (mol·K) respectively through magnetic field manipulation.

[0074] In practical refrigeration applications, a more critical indicator is the volume magnetic entropy density S. V It reflects the cooling capacity of a unit volume of material, the volumetric magnetic entropy density S V It can be calculated from the magnetic entropy change and material density using the following formula:

[0075] S V = S M ·ρ / M,

[0076] Ba6Nd2Ti4O 17 Ba6Gd2Ti4O 17 and Ba6Yb2Ti4O 17 The densities ρ of the three materials are 5.62 g / cm³. 35.82 g / cm 3 and 6.11 g / cm 3 The molar masses M are 1575.9 g / mol, 1601.9 g / mol, and 1633.5 g / mol, respectively. The calculated volume magnetic entropy density values ​​for the three materials are 41.1 mJ / (cm²). 3 ·K), 126 mJ / (cm 3 ·K) and 40.3 mJ / (cm 3 ·K).

[0077] Further analysis from the perspective of crystal structure reveals that Ba6Nd2Ti4O 17 Ba6Gd2Ti4O 17 and Ba6Yb2Ti4O 17 All three materials have Z=2 chemical formula units per unit cell, and their unit cell volumes V are 0.931 nm. 3 0.914 nm 3 and 0.888 nm 3 Therefore, the magnetic ion density can be calculated using the following formula:

[0078] n = Z·N / V,

[0079] Wherein, the magnetic ion density *n* refers to the number of magnetic ions per unit volume, and *N=2* represents the number of magnetic ions in each chemical unit cell of each material. Calculations yielded Ba6Nd2Ti4O... 17 Ba6Gd2Ti4O 17 and Ba6Yb2Ti4O 17 The magnetic ion densities of the three materials are 4.30 nm. -3 4.38 nm -3 and 4.50 nm -3 The high ion number density provides a structural basis for the material to achieve a large volumetric magnetic entropy density at low temperatures.

[0080] Therefore, the two-dimensional triangular lattice material Ba6Nd2Ti4O prepared in Examples 1-3 can be seen to be effective. 17 Ba6Gd2Ti4O 17 and Ba6Yb2Ti4O 17 The material can effectively absorb and release heat under magnetic field control, and has excellent low-temperature magnetocooling capability.

[0081] Example 5 Characterization of magnetic refrigeration performance

[0082] The two-dimensional triangular lattice material Ba6Nd2Ti4O prepared in Examples 1-3 17 Ba6Gd2Ti4O 17and Ba6Yb2Ti4O 17 The material was ground evenly and mixed evenly with silver powder. A pressure of 5MPa was applied under a tablet press for 2 hours to make a cylindrical block with a diameter of 12 mm. A thermometer was placed on its surface, and a polycrystalline thermal demagnetization test was performed in PPMS using a self-developed thermal demagnetization refrigeration measuring device.

[0083] For the two-dimensional triangular lattice material Ba6Nd2Ti4O prepared in Examples 1-3 17 Ba6Gd2Ti4O 17 and Ba6Yb2Ti4O 17 The material was demagnetized under different initial magnetic fields at an ambient temperature below 4 K. The temperature change curves after demagnetization are shown below. Figure 10-12 As shown. Once the magnetic field drops to zero, the lowest temperature for cooling can reach at least 25 mK, such as... Figure 12 As shown. For the two-dimensional triangular lattice material Ba6Nd2Ti4O prepared in Examples 1-2 with an effective mass of 3 g. 17 and Ba6Gd2Ti4O 17 The material, after the magnetic field drops to 0, can maintain its lowest temperature for hours, indicating that it has a large cooling capacity and is a good cryogenic magnetic refrigerant. Regarding the two-dimensional triangular lattice material Ba6Yb2Ti4O prepared in Example 3... 17 The material has a minimum cooling temperature of 25 mK and can maintain a temperature below 100 mK for at least 150 minutes with about 3 g of working fluid.

[0084] The above performance characterization results show that the novel magnetic refrigeration material Ba6Nd2Ti4O prepared according to this invention exhibits good performance. 17 Ba6Gd2Ti4O 17 and Ba6Yb2Ti4O 17 Compared to traditional magnetic refrigeration materials (hydrated paramagnetic salts), it has excellent magnetocaloric properties. In the actual adiabatic demagnetization test, it can achieve extremely low temperature refrigeration at the level of 100 mK and 10 mK. In the actual adiabatic demagnetization test, it can reach an extremely low temperature of 25 mK. At the same time, it has high stability, high magnetic entropy density, and is easy to prepare.

[0085] The above are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications or substitutions that are obvious to those skilled in the art should fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

[0086] Although the invention has been described and illustrated in conjunction with certain embodiments, it should be understood that various modifications of the invention will be apparent to those skilled in the art upon reading this specification. Therefore, it should be understood that the invention disclosed herein is intended to cover such modifications falling within the scope of the appended claims.

Claims

1. A two-dimensional triangular lattice of rare-earth based titanate polycrystalline material having a chemical formula of Ba6M2Ti4O 17 , and a space group of P63 / mmc, wherein M is one or more of Nd, Gd, and Yb.

2. The rare earth-based titanate polycrystalline material according to claim 1, wherein, M is Nd, and the lattice constants of the polycrystalline material are a=b=5.99 Å and c=29.93 Å; or M is Gd, and the lattice constants of the polycrystalline material are a=b=5.96 Å and c=29.70 Å; or M is Yb, and the lattice constants of the polycrystalline material are a=b=5.90 Å and c=29.40 Å.

3. The rare earth-based titanate polycrystalline material according to claim 1 or 2, wherein, M is Nd, and the rare earth-based titanate polycrystalline material has a Weiss temperature of about -0.051 K at 0.4 K - 1.2 K, an effective magnetic moment of 1.53 μ B ; or M is Gd, and the rare earth-based titanate polycrystalline material has a Weiss temperature of about -0.487 K at 0.46 K-1.33 K, an effective magnetic moment of 6.01 μ B ; or M is Yb, and the rare earth-based titanate polycrystalline material has a Weiss temperature of about -0.033 K at 0.4 K - 1.66 K, an effective magnetic moment of 1.69 μ B .

4. The rare earth-based titanate polycrystalline material according to any one of claims 1 to 3, wherein, M is Nd, and at a temperature of 0-2 K, the maximum magnetic entropy change of the rare earth-based titanate polycrystalline material regulated by a magnetic field is -ΔS≤11.53 J / (mol·K), the volume magnetic entropy density is 41.1 mJ / (cm 3 ·K), and the magnetic ion density is 4.30 nm -3 ; or When M is Gd, and at a temperature of 0-2 K, the maximum magnetic entropy change of the rare-earth-based titanate polycrystalline material controlled by a magnetic field is -ΔS≤34.58 J / (mol·K), and the volume magnetic entropy density is 126 mJ / (cm). 3 ·K), magnetic ion density is 4.38 nm -3 ;or When M is Yb, and at a temperature of 0-2 K, the maximum magnetic entropy change of the rare-earth-based titanate polycrystalline material controlled by a magnetic field is -ΔS≤11.53 J / (mol·K), and the volume magnetic entropy density is 40.3 mJ / (cm). 3 ·K), magnetic ion density is 4.50 nm -3 .

5. The rare-earth-based titanate polycrystalline material according to any one of claims 1 to 4, wherein, When M is Nd and the material is demagnetized from an initial magnetic field of 9 T at an initial temperature below 4 K, the temperature of the rare-earth-based titanate polycrystalline material reaches 42 mK when the magnetic field drops to zero; or M is Gd, and the rare earth-based titanate polycrystalline material is demagnetized from an initial magnetic field of 6 T at an initial temperature below 4 K. When the magnetic field drops to zero, the temperature of the rare earth-based titanate polycrystalline material reaches 126 mK. or M is Yb, and the rare earth-based titanate polycrystalline material is demagnetized from an initial magnetic field of 6 T at an initial temperature below 4 K. When the magnetic field drops to zero, the temperature of the material reaches 25 mK.

6. A method for preparing a two-dimensional triangular lattice rare-earth-based titanate polycrystalline material according to any one of claims 1 to 5, comprising the following steps: S1. Mix BaCO3, TiO2 and M2O3 according to the stoichiometric ratio, then preheat to 600-900℃ and maintain for 0-10 hours to obtain a preheated mixture; S2. The mixture obtained in step S1, which has been preheated, is heated again to 1000-1600°C and sintered at this temperature for at least 48 hours. After cooling to room temperature, it is then ground and compressed into tablets. S3. Repeat the preliminary heating and secondary heating steps at least once, and grind to obtain the rare earth-based titanate polycrystalline material.

7. The preparation method according to claim 6, wherein, The initial heating temperature is 800-900℃; Preferably, the secondary heating temperature is 1200-1500℃; Preferably, the sintering time is 48-96 hours; Preferably, the repeating step in step S3 is performed once.

8. The application of the two-dimensional triangular lattice rare-earth-based titanate polycrystalline material according to any one of claims 1 to 5, or the two-dimensional triangular lattice rare-earth-based titanate polycrystalline material prepared by the preparation method according to claim 6 or 7, as an adiabatic and demagnetizing refrigerant.

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