Van der Waals material as well as preparation method and application thereof

Abstract

The invention provides a Van der Waals material as well as a preparation method and application thereof. The Van der Waals material has a chemical formula shown as In2Ge2Se6 formula I, the Van der Waals material has a layered structure, and the interlayer total thermal conductivity and the intra-layer total thermal conductivity have anisotropy. The Van der Waals material provided by the invention has a unique bonding structure; a special multi-stage bonding system of strong covalent bonds in the layer and weak Van der Waals force in the layer is formed by adopting an interlayer confinement strategy, and meanwhile, the rigidity of the structure in the layer and the ultra-low heat conduction characteristic between the layers are kept. Under the condition of 600K, the interlayer thermal conductivity is only 0.20 W / m.K, the lowest record of an isomorphic Van der Waals material is created, and due to the characteristic, the material has potential application value in the fields of thermal management, novel thermal barrier coatings and efficient thermoelectric conversion devices.

Description

Technical Field

[0001] This invention belongs to the field of functional materials technology, and in particular relates to a van der Waals material, its preparation method and application. Background Technology

[0002] Thermal conductivity is an important indicator for measuring the thermal conductivity of a material. Low thermal conductivity materials have wide applications in many fields. For example, in thermoelectric energy, low thermal conductivity materials can improve the thermoelectric figure of merit (ZT), achieving more efficient thermoelectric conversion; in heat dissipation of electronic devices, anisotropic thermal conductivity materials can optimize thermal management design; and in aerospace, stable low thermal conductivity materials can serve as novel thermal barrier coatings. While traditional van der Waals materials such as graphene and molybdenum disulfide possess unique layered structures and excellent electrical properties, their thermal conductivity often fails to meet the requirements of specific applications.

[0003] In existing technologies, researchers typically reduce the thermal conductivity of materials by introducing asymmetric structural units or constructing weak chemical bonds. For example, creating pores and defects in graphene, introducing sp3 hybrid carbon atoms, or doping molybdenum disulfide with large-sized heteroatoms can indeed significantly reduce the lattice thermal conductivity of materials. However, such structural modifications often lead to decreased material stability, manifested as reduced mechanical strength, weakened oxidation resistance, or structural degradation at high temperatures. Furthermore, many modification methods require complex synthesis processes, such as precisely controlled chemical vapor deposition, high-energy ion irradiation, or multi-step solution treatments, which not only increase preparation costs but also reduce the reproducibility and feasibility of large-scale production. Therefore, developing novel van der Waals materials that combine excellent thermal properties with good stability is of great significance. Summary of the Invention

[0004] The purpose of this invention is to provide a van der Waals material, its preparation method and application. The van der Waals material of this invention exhibits significant anisotropy in the total thermal conductivity between and within the layers, and has extremely low interlayer thermal conductivity and excellent stability.

[0005] This invention provides a van der Waals material having the chemical formula shown in Formula I:

[0006] In2Ge2Se6 formula I;

[0007] The van der Waals material has a layered structure, and the total thermal conductivity between layers and the total thermal conductivity within layers are anisotropic.

[0008] Preferably, the total interlayer thermal conductivity of the van der Waals material is ≤0.65 W / m / K between 300 and 600 K.

[0009] Preferably, the van der Waals material has a single-crystal structure.

[0010] This invention provides a method for preparing van der Waals materials as described above, comprising the following steps:

[0011] A) Mix elemental In, elemental Ge, and elemental Se and place them in a first quartz tube;

[0012] The molar ratio of In, Ge, and Se is 2:2:6;

[0013] B) The first quartz tube is placed inside the second quartz tube, the tube is sealed under vacuum, and then the second quartz tube is placed in a dual-temperature zone tube furnace for high-temperature sintering to obtain van der Waals material.

[0014] Preferably, the diameter of the second quartz tube is 5 to 100 mm larger than the diameter of the first quartz tube.

[0015] Preferably, in step B), one or more vacuum-sealed first quartz tubes are placed inside a second quartz tube, so that the mixture inside the first quartz tube is located at the hot end of the dual-temperature zone tube furnace, and then the tube is vacuum-sealed.

[0016] Preferably, the sintering in step B) is performed according to the following procedure:

[0017] Heating stage: The hot end of the dual-temperature zone tubular furnace is heated from room temperature to 750-755°C, and the cold end of the dual-temperature zone tubular furnace is heated from room temperature to 550-560°C.

[0018] Insulation stage: The hot and cold ends of the dual-temperature zone tubular furnace are simultaneously insulated for 80 to 130 hours after heating.

[0019] Cooling stage: The hot end of the dual-temperature zone tubular furnace cools down from 750-755°C to room temperature, and the cold end of the dual-temperature zone tubular furnace cools down from 550-560°C to room temperature.

[0020] Preferably, during the heating stage, the heating rate of the hot end is 1-2℃ / min, and the heating rate of the cold end is 1-2℃ / min.

[0021] During the cooling stage, the cooling rate of the hot end is 1-2℃ / min, and the cooling rate of the cold end is 1-2℃ / min.

[0022] Preferably, the vacuum level during vacuum sealing in step B) is 10. -5 ~10 -6 Torr.

[0023] This invention provides an application of the van der Waals material as described above as a low thermal conductivity material.

[0024] This invention provides a van der Waals material with the chemical formula: In₂Ge₂Se₆ (Formula I). ​​The van der Waals material has a layered structure, and both the interlayer and intralayer total thermal conductivity exhibit anisotropy. The van der Waals material of this invention possesses a unique bonding structure: it employs an "interlayer confinement" strategy to form a special multi-level bonding system with strong intralayer covalent bonds and weak interlayer van der Waals forces, while maintaining the rigidity of the intralayer structure and ultra-low interlayer thermal conductivity. At 600K, its interlayer thermal conductivity is only 0.20 W / m·K, setting a record for the lowest among isomorphic van der Waals materials. This characteristic makes it potentially valuable in the fields of thermal management, novel thermal barrier coatings, and high-efficiency thermoelectric conversion devices. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0026] Figure 1 This is a photograph of the single crystal sample obtained in Example 1 of the present invention;

[0027] Figure 2 This is a scanning electron microscope (SEM) image of the sample obtained in Example 2 of the present invention;

[0028] Figure 3 These are partial single-crystal photographs of the novel van der Waals material In2Ge2Se6 prepared in Example 2 of this invention;

[0029] Figure 4 This is a photograph of the single crystal sample obtained in Example 3 of the present invention;

[0030] Figure 5 The X-ray diffraction (XRD) pattern of the sample obtained in Example 4 of this invention;

[0031] Figure 6 High-angle annular dark-field scanning transmission electron microscopy (HAADF) image of the sample obtained in Example 5 of this invention;

[0032] Figure 7 This is an image showing the X-ray photoelectron spectroscopy (XPS) test results of the sample obtained in Example 5 of this invention.

[0033] Figure 8 The image shows the thermal analysis TG-DSC test results of the sample obtained in Example 5 of this invention.

[0034] Figure 9 This is a graph showing the polarization Raman spectroscopy results of the sample obtained in Example 5 of the present invention.

[0035] Figure 10 This is a graph showing the thermal conductivity κ test results of the sample obtained in Example 5 of the present invention.

[0036] Figure 11 This is a comparison diagram of the thermal conductivity κ of the sample obtained in Example 5 of the present invention and the isomorphic material. Detailed Implementation

[0037] This invention provides a van der Waals material having the chemical formula shown below:

[0038] In2Ge2Se6 formula I;

[0039] The van der Waals material has a layered structure, and the total thermal conductivity between layers and the total thermal conductivity within layers are anisotropic.

[0040] In this invention, the van der Waals material is a layered semiconductor with a crystal structure. The van der Waals material has an extremely low total interlayer thermal conductivity in the temperature range of 300 to 600 K, which is ≤0.65 W / m / K, more preferably 0.65 to 0.20 W / m / K, and the total intralayer thermal conductivity is as high as 4.29 W / m / K at room temperature.

[0041] The present invention also provides a method for preparing the van der Waals material described above, comprising the following steps:

[0042] A) Mix In, Ge, and Se elements, place them in a first quartz tube, and seal the tube under vacuum.

[0043] The molar ratio of In, Ge, and Se is 2:(2-3):6;

[0044] B) The first quartz tube, which is vacuum-sealed, is placed inside the second quartz tube. The second quartz tube is then vacuum-sealed, and then placed in a dual-temperature zone tube furnace for high-temperature sintering to obtain van der Waals material.

[0045] In this invention, the In, Ge, and Se elements are respectively high-purity powdered Ge, high-purity powdered In, and high-purity powdered Se elements, and the purity of the In, Ge, and Se elements is all >99.99%. In this invention, the molar ratio of the In, Ge, and Se elements is preferably 2:(2-3):6, such as 2:2:6 or 2:3:6.

[0046] In this invention, the vacuum level of the first quartz tube is preferably 10. -5 ~10 -6Torr; The diameter and length of the first quartz tube are both smaller than those of the second quartz tube, so that the second quartz tube can accommodate one or more first quartz tubes. Preferably, the diameter of the second quartz tube is 5 to 100 mm larger than that of the first quartz tube, more preferably 5 to 50 mm, and most preferably 5 to 20 mm.

[0047] This invention involves inserting one or more first quartz tubes filled with a mixture into a second quartz tube and sealing the tubes under vacuum. Alternatively, this invention can sinter multiple first quartz tubes into a second quartz tube, enabling the simultaneous preparation of a large number of single-crystal samples.

[0048] In this invention, the vacuum level of the second quartz tube is preferably 10. -5 ~10 -6 Torr.

[0049] This invention involves placing a vacuum-sealed second quartz tube in a dual-temperature zone tube furnace for high-temperature sintering to obtain van der Waals material.

[0050] In this invention, the dual-temperature zone tube furnace has a hot end and a cold end, with the mixture inside the first quartz tube located at the hot end. The high-temperature sintering is preferably performed according to the following steps:

[0051] Heating stage: The hot end of the dual-temperature zone tubular furnace is heated from room temperature to 750-755°C, and the cold end of the dual-temperature zone tubular furnace is heated from room temperature to 550-560°C.

[0052] Insulation stage: The hot and cold ends of the dual-temperature zone tubular furnace are simultaneously insulated for 80 to 130 hours after heating.

[0053] Cooling stage: The hot end of the dual-temperature zone tubular furnace cools down from 750-755°C to room temperature, and the cold end of the dual-temperature zone tubular furnace cools down from 550-560°C to room temperature.

[0054] In this invention, the heat preservation temperature of the hot end is preferably 750–755℃, such as 750℃, 751℃, 752℃, 753℃, 754℃, 755℃, preferably within a range where any of the above values ​​are the upper or lower limits; the heating rate of the hot end is preferably 1–2℃ / min; the cooling rate of the hot end is preferably 1–2℃ / min, or naturally cooled to room temperature; the heat preservation time of the hot end is preferably 80–130 hours, more preferably 90–120 hours, such as 80 hours, 90 hours, 100 hours, 110 hours, 120 hours, 130 hours, preferably within a range where any of the above values ​​are the upper or lower limits; the heat preservation temperature of the cold end is preferably 550–560℃, such as 550℃, 751℃, 752℃, 753℃, 754℃, 755℃, preferably within a range where any of the above values ​​are the upper or lower limits; The temperatures are 0℃, 551℃, 552℃, 553℃, 554℃, 555℃, 556℃, 557℃, 558℃, 559℃, and 560℃, preferably within a range where any of the above values ​​is the upper or lower limit; the heating rate of the cold end is preferably 1-2℃ / min; the cooling rate of the cold end is preferably 1-2℃ / min, or naturally cooled to room temperature; the holding time of the cold end is preferably 80-130 hours, more preferably 90-120 hours, such as 80 hours, 90 hours, 100 hours, 110 hours, 120 hours, and 130 hours, preferably within a range where any of the above values ​​is the upper or lower limit; in this invention, the holding time of the cold end is preferably equal to the holding time of the hot end.

[0055] The present invention also provides an application of the van der Waals material described above as a low thermal conductivity material in thermal barrier coatings, thermoelectric conversion, or heat dissipation devices for electronic devices.

[0056] This invention provides a van der Waals material with the chemical formula: In₂Ge₂Se₆ (Formula I). ​​The van der Waals material has a layered structure, and both the interlayer and intralayer total thermal conductivity exhibit anisotropy. The van der Waals material of this invention possesses a unique bonding structure: it employs an "interlayer confinement" strategy to form a special multi-level bonding system with strong intralayer covalent bonds and weak interlayer van der Waals forces, while maintaining the rigidity of the intralayer structure and ultra-low interlayer thermal conductivity. At 600K, its interlayer thermal conductivity is only 0.20 W / m·K, setting a record for the lowest among isomorphic van der Waals materials. This characteristic makes it potentially valuable in the fields of thermal management, novel thermal barrier coatings, and high-efficiency thermoelectric conversion devices.

[0057] To further illustrate the present invention, the following detailed description of a van der Waals material, its preparation method, and its application, in conjunction with embodiments, is provided by the present invention, but should not be construed as limiting the scope of protection of the present invention.

[0058] There are no particular restrictions on the source of any raw materials used in this invention; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0059] This invention uses high-purity powdered Ge, powdered In, and powdered Se as starting materials, wherein the purity of the starting materials is >99.99%.

[0060] Example 1

[0061] In, Ge, and Se were weighed and mixed in a molar ratio of 2:3:6 to obtain 0.3g of the mixture. The mixture was then placed into a quartz tube with a diameter of 10mm. The quartz tube containing the mixture was then placed into a quartz tube with a diameter of 15mm and sealed under vacuum.

[0062] The vacuum-sealed 15mm quartz tube was placed in a dual-zone tube furnace, with the bottom end of the 15mm quartz tube positioned at the hot end of the furnace. The hot end of the furnace was heated from room temperature to 800°C at a rate of 4°C / min, while the cold end was heated from room temperature to 600°C at a rate of 2°C / min. Both ends of the furnace were held at these temperatures simultaneously for 50 hours. Next, both the hot and cold ends of the furnace were allowed to cool naturally to room temperature. Finally, after cooling to room temperature, a single crystal sample of the novel van der Waals material was obtained in a 10mm quartz tube with a feed ratio of 2 / 3 / 6. Figure 1 The size is approximately 0.5mm.

[0063] Example 2

[0064] In, Ge, and Se were weighed and mixed in a molar ratio of 2:3:6 to obtain 0.3g of the mixture. The mixture was then placed into a quartz tube with a diameter of 10mm. The quartz tube containing the mixture was then placed into a quartz tube with a diameter of 15mm and sealed under vacuum.

[0065] The vacuum-sealed 15mm quartz tube was placed in a dual-zone tube furnace, with the bottom end of the 15mm quartz tube positioned at the hot end of the furnace. The hot end of the furnace was heated from room temperature to 750°C at a rate of 2°C / min, while the cold end was heated from room temperature to 560°C at a rate of 2°C / min. Both ends of the furnace were then held at these temperatures for 80 hours. Next, the hot end of the furnace was cooled from 750°C to room temperature at a rate of 2°C / min, and the cold end was cooled from 560°C to room temperature at a rate of 2°C / min. Finally, after cooling to room temperature, the novel van der Waals material was obtained in a 10mm quartz tube with a feed ratio of 2 / 2 / 6.

[0066] Example 3

[0067] In, Ge, and Se were weighed and mixed in a molar ratio of 2:2:6 to obtain 0.3g of the mixture. The mixture was then placed into a quartz tube with a diameter of 10mm. The quartz tube containing the mixture was then placed into a quartz tube with a diameter of 15mm and sealed under vacuum.

[0068] The vacuum-sealed 15mm quartz tube was placed in a dual-zone tube furnace, with the bottom end of the 15mm quartz tube positioned at the hot end of the furnace. The hot end of the furnace was heated from room temperature to 750°C at a rate of 2°C / min, while the cold end was heated from room temperature to 560°C at a rate of 2°C / min. Both ends of the furnace were then held at these temperatures for 80 hours. Next, the hot end of the furnace was cooled from 750°C to room temperature at a rate of 2°C / min, and the cold end was cooled from 560°C to room temperature at a rate of 2°C / min. Finally, after cooling to room temperature, the novel van der Waals material was obtained in a 10mm quartz tube with a feed ratio of 2 / 2 / 6. (See [reference needed]). Figure 3 The crystals are approximately 1 mm in size, and some single crystals exhibit stacking fault growth defects.

[0069] Example 4

[0070] In, Ge, and Se were weighed and mixed in a molar ratio of 2:2:6 to obtain 0.5g of the mixture. The mixture was then placed into a quartz tube with a diameter of 10mm. The quartz tube containing the mixture was then placed into a quartz tube with a diameter of 15mm and sealed under vacuum.

[0071] The vacuum-sealed 15mm quartz tube was placed in a dual-zone tube furnace, with the bottom end of the 15mm quartz tube positioned at the hot end of the furnace. The hot end of the furnace was heated from room temperature to 750°C at a rate of 2°C / min, while the cold end was heated from room temperature to 560°C at a rate of 2°C / min. Both ends of the furnace were then held at these temperatures for 80 hours. Next, the hot end of the furnace was cooled from 750°C to room temperature at a rate of 2°C / min, and the cold end was cooled from 560°C to room temperature at a rate of 2°C / min. Finally, after cooling to room temperature, the novel van der Waals material was obtained in a 10mm quartz tube with a feed ratio of 2 / 2 / 6, with some single crystals exhibiting stacking fault growth defects.

[0072] Example 5

[0073] In, Ge, and Se were weighed and mixed in a molar ratio of 2:2:6 to obtain 1.0 g of mixture. The mixture was then placed into a quartz tube with a diameter of 10 mm. The quartz tube containing the mixture was then placed into a quartz tube with a diameter of 15 mm and sealed under vacuum.

[0074] The vacuum-sealed 15mm quartz tube was placed in a dual-zone tube furnace, with the bottom end of the tube positioned at the hot end. The hot end of the furnace was heated from room temperature to 755°C at a rate of 1°C / min, while the cold end was heated from room temperature to 560°C at a rate of 1°C / min. Both ends were then held at these temperatures for 120 hours. Next, the hot end was cooled from 755°C to room temperature at a rate of 1°C / min, and the cold end was cooled from 560°C to room temperature at a rate of 1°C / min. Finally, after cooling to room temperature, a single crystal sample of the novel van der Waals material was obtained.

[0075] Example 6

[0076] The novel van der Waals material prepared in Example 5 was characterized by phase composition and thermal conductivity testing. The results are shown in the figure. Figures 5-9 .

[0077] Figure 1 This is a photograph of a single crystal sample of the novel van der Waals material In2Ge2Se6 prepared in Example 1 of this invention; Figure 1 It can be seen that single-crystal samples can be obtained through this solid-state synthesis method, but under the preparation conditions in Example 1, the yield of single crystals of the novel van der Waals material In2Ge2Se6 is very low.

[0078] Figure 2 The above are the SEM test results of the novel van der Waals material In2Ge2Se6 prepared in Example 2 of this invention; Figure 3 These are partial single-crystal photographs of the novel van der Waals material In2Ge2Se6 prepared in Example 2 of this invention. Figures 2-3 It can be seen that, based on the preliminary exploration of Example 1, Example 2 further improved the process and obtained the new compound in this invention - the novel van der Waals material In2Ge2Se6, and the yield was increased compared with Example 1, and the single crystal size was also increased to the millimeter level.

[0079] Figure 4 This is a photograph of a single crystal sample of the novel van der Waals material In2Ge2Se6 prepared in Example 3 of this invention; Figure 4It can be seen that: through the exploration of the preparation of the novel van der Waals material In2Ge2Se6 in Examples 1 and 2, the optimized synthesis conditions of the novel van der Waals material In2Ge2Se6 were screened, and a large number of single crystal samples can be obtained.

[0080] Figure 5 The X-ray diffraction test results are for the novel van der Waals material In2Ge2Se6 single crystal sample prepared in Example 4 of this invention. Figure 5 It can be seen that the single crystal sample contains In-Se covalent bonds, weak interlayer van der Waals interactions, and a Ge-Ge metallic bond multi-bonding system.

[0081] Figure 6 The HAADF test results are for the novel van der Waals material In2Ge2Se6 prepared in Example 5 of this invention.

[0082] Figure 7 The above are the X-ray photoelectron spectroscopy (XPS) test results of the novel van der Waals material In2Ge2Se6 prepared in Example 5 of this invention; Figure 7 It can be seen that in In2Ge2Se6, the valence states of the three elements In, Ge and Se are 3+, 3+ and 2-, respectively.

[0083] Figure 8 The results of thermal analysis (TG-DSC) of the novel van der Waals material In2Ge2Se6 prepared in Example 5 of this invention are shown. Figure 8 It can be seen that In2Ge2Se6 has good thermal stability in the temperature range of room temperature to 500℃.

[0084] Figure 9 The polarization Raman spectroscopy results are for the novel van der Waals material In2Ge2Se6 prepared in Example 5 of this invention; Figure 9 We know that: 103.17cm -1 (P1), 128.82cm -1 (P2) and 277.70cm -1 The phonon mode of (P5) is designated as E g The characteristic modulus, and 153.45cm -1 (P3) and 191.97cm -1 (P4) is A g Feature mode.

[0085] Figure 10 The thermal conductivity test results are for the novel van der Waals material In2Ge2Se6 prepared in Example 5 of this invention; Figure 10It can be seen that the In2Ge2Se6 single crystal sample has an extremely low interlayer total thermal conductivity of 0.65~0.20 W / m / K in the temperature range of 300-600K, while the intralayer total thermal conductivity is as high as 4.29 W / m / K at room temperature.

[0086] Figure 11 This is a comparison chart showing the thermal conductivity test results of the novel van der Waals material In2Ge2Se6 prepared in Example 5 of this invention with that of isomorphic materials obtained by the traditional solid-state synthesis method (ball milling + annealing); Figure 11 It can be seen that In₂Ge₂Se₆ exhibits the lowest thermal conductivity among all the compared isomorphic materials, a result that fully demonstrates its significant advantage in thermal conductivity. As can be seen from the above embodiments, the novel van der Waals material provided by this invention has the chemical formula: In₂Ge₂Se₆ (Formula I). ​​It possesses extremely low interlayer thermal conductivity, with a value as low as ~0.20 W / m / K at 600 K. Simultaneously, the material exhibits significant anisotropy in both interlayer and intralayer total thermal conductivity, making it a novel low-dimensional solid material with novel thermophysical properties.

[0087] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A van der Waals material having the chemical formula shown in Formula I: In2Ge2Se6 formula I; The van der Waals material has a layered structure, and the total thermal conductivity between layers and the total thermal conductivity within layers are anisotropic.

2. The van der Waals material according to claim 1, characterized in that, Between 300 and 600 K, the total interlayer thermal conductivity of the van der Waals material is ≤0.65 W / m / K.

3. The van der Waals material according to claim 1, characterized in that, The van der Waals material has a single-crystal structure.

4. The method for preparing van der Waals material as described in claim 1, comprising the following steps: A) Mix elemental In, elemental Ge, and elemental Se and place them in a first quartz tube; The molar ratio of In, Ge, and Se is 2:2:6; B) The first quartz tube is placed inside the second quartz tube, the tube is sealed under vacuum, and then the second quartz tube is placed in a dual-temperature zone tube furnace for high-temperature sintering to obtain van der Waals material.

5. The preparation method according to claim 4, characterized in that, The diameter of the second quartz tube is 5 to 100 mm larger than that of the first quartz tube.

6. The preparation method according to claim 4, characterized in that, In step B), one or more vacuum-sealed first quartz tubes are placed inside a second quartz tube, so that the mixture inside the first quartz tube is located at the hot end of the dual-temperature zone tube furnace, and then the tube is vacuum-sealed.

7. The preparation method according to claim 4, characterized in that, The sintering in step B) is performed according to the following procedure: Heating stage: The hot end of the dual-temperature zone tubular furnace is heated from room temperature to 750-755°C, and the cold end of the dual-temperature zone tubular furnace is heated from room temperature to 550-560°C. Insulation stage: The hot and cold ends of the dual-temperature zone tubular furnace are simultaneously insulated for 80 to 130 hours after heating. Cooling stage: The hot end of the dual-temperature zone tubular furnace cools down from 750-755°C to room temperature, and the cold end of the dual-temperature zone tubular furnace cools down from 550-560°C to room temperature.

8. The preparation method according to claim 7, characterized in that, During the heating stage, the heating rate of the hot end is 1-2℃ / min, and the heating rate of the cold end is 1-2℃ / min. During the cooling stage, the cooling rate of the hot end is 1-2℃ / min, and the cooling rate of the cold end is 1-2℃ / min.

9. The preparation method according to claim 4, characterized in that, The vacuum level for vacuum sealing in step B) is preferably 10. -5 ~10 -6 Torr.

10. An application of the van der Waals material as described in claim 1 as a low thermal conductivity material.

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