Method and Application for Synthesizing Van der Waals Mismatched Layered Compounds Based on Solid-State High-Temperature Synthesis

Abstract

The present invention provides a method and application for synthesizing van der Waals misaligned layered compounds based on solid-state high-temperature synthesis, belonging to the technical field of functional devices. The compound is composed of at least two van der Waals material sublayers; in terms of the preparation method, a structure existing under thermodynamically stable conditions is synthesized through high-temperature sintering to achieve the alternating self-assembly growth of heterogeneous structures; in terms of application, a functional device application regulation system is constructed to realize the application of the compound in fields such as lateral ferroelectric metal memristors, vertical piezoelectric devices, superconducting ferroelectric memristor devices, etc. The present invention solves the problems of complex process, low efficiency, and high cost in the traditional preparation of van der Waals misaligned layered compounds, constructs a functional device application regulation system, realizes its wide application in multiple fields, and provides a brand-new direction for the future development of science and technology.

Description

Technical Field

[0001] The present invention relates to the technical field of functional devices, and particularly to a method for synthesizing van der Waals misfit layered compounds based on solid-state high-temperature synthesis and its applications. Background Art

[0002] In recent years, van der Waals (vdW) materials and misfit layered compounds have attracted much attention in the field of materials research. Van der Waals materials are layered materials held together by van der Waals forces. Their unique layered structure endows them with many excellent properties, such as high flexibility and tunable electrical properties. Misfit layered compounds are composed of two-dimensional components with different lattice constants interleaved. For misfit layered compounds based on two-dimensional vdW materials, due to the weak van der Waals forces between layers, each component can retain its intrinsic properties, enabling the integration of multiple characteristics, and thus showing great potential in the field of future functional devices.

[0003] The emergence of two-dimensional vdW layered ferroelectric materials has opened up a new direction for the design of future all-two-dimensional material heterostructure non-volatile devices. Such materials not only possess the stable spontaneous polarization and strong nonlinear characteristics of traditional ferroelectric materials but also have unique advantages. Their bandgap range can be adjusted, which is of great significance in optoelectronic devices and enables flexible control of the absorption and emission of light with different wavelengths. At the same time, they also have non-trivial quantum topological physical properties, providing new material options for research in frontier fields such as quantum computing and quantum communication. Therefore, novel vdW ferroelectrics are regarded as highly potential candidate materials for post-Moore's law electronics and optoelectronic devices, showing broad application prospects in multiple fields such as high-density integrated ferroelectric memory, neuromorphic computing, optoelectronic sensing and computing integrated chips, nanogenerators, and photovoltaic devices.

[0004] However, the current research on vdW materials is unevenly developed. Although a large number of research results have been obtained in terms of optical and electrical properties, and researchers have a relatively in-depth understanding of their optical absorption, emission mechanisms, and electrical conduction characteristics, the exploration of ferroelectricity is still in a relatively early stage. Many issues regarding the basic properties of vdW ferroelectric materials, ferroelectric phase transition mechanisms, and coupling relationships with other physical properties have not been fully studied and clearly answered, which to a certain extent limits the optimized design and performance improvement of vdW ferroelectric materials in related devices.

[0005] In terms of material preparation processes, traditional heterogeneous superlattice crystal preparation mostly adopts a layer-by-layer preparation process. This process forms crystals by stacking materials layer by layer, and exposes many drawbacks in the actual operation process. The low deposition rate leads to low production efficiency and is difficult to meet the needs of large-scale industrial production; poor scalability makes it face many difficulties in preparing crystals with large sizes or complex structures; poor stability is easily affected by external environmental factors, resulting in uneven crystal quality; moreover, the material selection is limited, and only specific matching materials can be selected for layer-by-layer stacking, which greatly limits the development and application potential of new material systems and is difficult to meet the growing demand for high-performance and multifunctional materials. Summary of the Invention

[0006] In order to overcome the deficiencies of the prior art, the present invention provides a method and application for preparing van der Waals misfit layered compounds based on solid-state high-temperature synthesis, solves the problems of complex process, low efficiency and high cost in the traditional preparation of van der Waals misfit layered compounds, constructs a functional device application regulation system, realizes its wide application in multiple fields, and provides a new direction for the future development of science and technology.

[0007] To achieve the above object, the present invention provides the following solutions:

[0008] The first object of the present invention is to provide a van der Waals misfit layered compound based on solid-state high-temperature synthesis. The van der Waals misfit layered compound is prepared by a solid-state high-temperature synthesis method and is composed of at least two van der Waals material sub-layers. One of the van der Waals material sub-layers is a compound layer containing a Group IV or Group V transition metal, and the other van der Waals material sub-layer is a compound layer containing an element such as tin, lead, bismuth, antimony or a rare earth metal, and the atoms between the two van der Waals material sub-layers are connected by van der Waals forces.

[0009] Preferably, the general chemical formula of the van der Waals misfit layered compound is ([MX] 1+δ ) m (TX2) n ; where M is any one of the elements such as tin, lead, bismuth, antimony or a rare earth metal, T is a Group IV or Group V transition metal element, X is a sulfur element or a selenium element, the parameter δ is the in-plane area ratio of the two components, m is the stoichiometric number of the MX layer, and n is the stoichiometric number of the TX2 layer.

[0010] Preferably, the two van der Waals material sub-layers are a tetragonal phase layer A and a hexagonal phase layer B, and form a heterogeneous superlattice according to the stacking modes of ABAB and AAB; the crystal structure of the van der Waals misfit layered compound is jointly characterized by Raman spectroscopy and scanning transmission electron microscopy-high angle annular dark field, and contains two-dimensional components with two different lattice constants, and shows a staggered arrangement to form a misfit layered structure.

[0011] A second object of the present invention is to provide a method for preparing the above-mentioned van der Waals misaligned layered compound based on solid-state high-temperature synthesis, comprising the following steps:

[0012] According to the chemical formula of the target compound, weigh elemental single powders as starting materials, and mix them evenly to obtain a mixed powder;

[0013] Co-encapsulate the mixed powder and a transport agent in a vacuum-sealed quartz tube;

[0014] Place the encapsulated quartz tube in a two-zone furnace, and set the temperatures of the precursor mixture source end and the crystal growth end. Use chemical vapor transport method to make the mixed powder react and crystallize and grow in a gas-phase environment;

[0015] After the reaction is completed, take out the quartz tube from the two-zone furnace and perform quenching treatment to cool the crystal in the quartz tube from the reaction temperature to room temperature, fix the crystal structure, and obtain a single crystal of van der Waals misaligned layered compound, that is, obtain a van der Waals misaligned layered compound.

[0016] Preferably, the transport agent is a stannous halide compound, and the stannous halide compound is one of stannous chloride and stannous bromide.

[0017] Preferably, the temperature range of the precursor mixture source end is 800-900 °C; the temperature range of the crystal growth end is 750-850 °C; use chemical vapor transport method for crystal growth, and the growth time is 7-14 days.

[0018] A third object of the present invention is to provide an application of the above-mentioned van der Waals misaligned layered compound, which is applied to a variety of functional devices based on the electrical properties of the van der Waals misaligned layered compound, specifically including: lateral ferroelectric metal memristors, vertical piezoelectric devices, superconducting ferroelectric memristive devices.

[0019] Preferably, the in-plane ferroelectric tunnel junction of the van der Waals misaligned layered compound has a hysteresis current-voltage hysteresis curve with a low threshold voltage, and thus is applied to a lateral ferroelectric metal memristor with low energy consumption.

[0020] Preferably, the crystal structure of the van der Waals misaligned layered compound has the characteristic of out-of-plane symmetry breaking due to the mismatch of two sub-layer lattices, and generates deformation along the electric field direction under the action of an electric field, and is applied to a vertical piezoelectric device with high-efficiency electromechanical conversion performance.

[0021] Preferably, the van der Waals misaligned layered compound is an Ising superconductor, which has the characteristic of a high upper critical field, and thus remains in a stable superconducting state in a strong magnetic field environment, and is applied to a superconducting ferroelectric memristive device with high stability.

[0022] According to the specific embodiments provided by the present invention, the following technical effects are disclosed by the present invention:

[0023] (1) A preparation method of a van der Waals misaligned coordination layered compound based on solid-state high-temperature synthesis provided by the present invention simplifies the traditional preparation process by precisely controlling the stoichiometric ratios of various elements, selecting a suitable transport agent, sintering and growing the compound in a high-temperature zone by means of chemical vapor transport method, and stabilizing its structure and properties by using a quenching process at the reaction temperature. It overcomes the cumbersome nature of the layer-by-layer preparation process, improves the preparation efficiency and stability, has higher potential for industrial application, can achieve large-scale production at lower cost, and lays a solid foundation for the extensive research and application of the compound.

[0024] (2) The van der Waals misaligned coordination layered compound provided by the present invention shows great application potential in the field of functional devices, especially in frontier science and technology fields such as artificial intelligence. This compound can be used to construct non-volatile electronic devices, providing the possibility for realizing a brain-inspired architecture with in-memory computing; specifically, by constructing lateral ferroelectric metal memristors, vertical piezoelectric devices, superconducting ferroelectric memory resistive devices, etc., it meets the requirements of brain-inspired computing and neural networks for high-performance devices, promotes the development of artificial intelligence hardware, and provides a new direction for the innovation of future technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0026] Figure 1 It is a flow chart of a preparation method of a van der Waals misaligned coordination layered compound based on solid-state high-temperature synthesis according to the present invention;

[0027] Figure 2 It is (SnSe) provided in Embodiment 1 of the present invention 1.16 X-ray diffraction pattern of the (NbSe2) crystal;

[0028] Figure 3 It is (SnSe) provided in Embodiment 1 of the present invention 1.16 STEM-HAADF image of the (NbSe2) crystal;

[0029] Figure 4 It is the ferroelectric property image of the (SnSe) 1.16 (NbSe2) crystal obtained by using a lateral piezoresponse force microscope in Embodiment 1 of the present invention; wherein, Figure 4 (a) in it is a local electrical switching polarization spectrum, Figure 4Among them, (b) is the in-plane phase diagram in a figure-eight shape, Figure 4 and (c) is the amplitude electric domain diagram;

[0030] Figure 5 This is the piezoelectric effect diagram of (SnSe) 1.16 (NbSe2) crystal obtained by using a vertical piezoresponse force microscope provided in Embodiment 1 of the present invention;

[0031] Figure 6 This is the electronic structure diagram of (SnSe) 1.16 (NbSe2) crystal obtained by using angle-resolved photoemission spectroscopy provided in Embodiment 1 of the present invention; Among them, Figure 6 in (a), it is the relationship diagram between the binding energy and the in-plane wave vector of (SnSe) 1.16 (NbSe2) crystal under 45 eV excitation, k / / ; Figure 6 in (b), it is the relationship diagram between the binding energy and the in-plane wave vector of (SnSe) 1.16 (NbSe2) crystal under 40 eV excitation, k / / ; Figure 6 in (c), it is the relationship diagram between the binding energy and the in-plane wave vector of (SnSe) 1.16 (NbSe2) crystal under 35 eV excitation, k / / ; Figure 6 in (d), it is the relationship diagram between the binding energy and the in-plane wave vector of (SnSe) 1.16 (NbSe2) crystal under 30 eV excitation, k / / ; Figure 6 in (e), it is the relationship diagram between the binding energy and the in-plane wave vector of (SnSe) 1.16 (NbSe2) crystal under 25 eV excitation, k / / ;

[0032] Figure 7 This is the structure diagram of the in-plane ferroelectric tunnel junction device provided in Embodiment 4 of the present invention; Among them, Figure 7 in (a), it is the overall structure schematic diagram of the in-plane ferroelectric tunnel junction device, Figure 7 and in (b), it is the physical diagram of the in-plane ferroelectric tunnel junction device;

[0033] Figure 8 This is the performance diagram of the in-plane ferroelectric tunnel junction provided in Embodiment 4 of the present invention; Among them, Figure 8 in (a), it is the I-V hysteresis curve diagram, Figure 8 and in (b), it is the asymmetric current switching diagram;

[0034] Figure 9 The structural and performance test diagram of the piezoelectric device provided in Embodiment 4 of the present invention; among them, Figure 9 in (a) is the schematic structural diagram of the piezoelectric device, Figure 9 in (b) is the piezoelectric performance diagram of the piezoelectric device. Detailed implementation manners

[0035] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0036] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0037] As Figure 1 shown, the present invention provides a preparation method of a van der Waals misaligned coordination layered compound based on solid-state high-temperature synthesis, including the following steps:

[0038] Step 100: According to the chemical formula of the target compound, weigh the elemental single powder as the starting material and mix them evenly to obtain a mixed powder;

[0039] Step 200: Co-encapsulate the mixed powder and the transport agent in a vacuum-sealed quartz tube;

[0040] Step 300: Place the encapsulated quartz tube in a two-temperature zone furnace, set the temperatures of the precursor mixture source end and the crystal growth end, and use chemical vapor transport method to react and crystallize the mixed powder in a gas phase environment;

[0041] Step 400: After the reaction is completed, take out the quartz tube from the two-temperature zone furnace and perform quenching treatment to cool the crystal in the quartz tube from the reaction temperature to room temperature, fix the crystal structure, and obtain a single crystal of van der Waals misaligned coordination layered compound, that is, obtain a van der Waals misaligned coordination layered compound.

[0042] In the above steps, the transport agent is a stannous halide compound, and the stannous halide compound is selected from one of stannous chloride and stannous bromide. The temperature range of the precursor mixture source end is 800-900 °C; the temperature range of the crystal growth end is 750-850 °C; the chemical vapor transport method is used for crystal growth, and the growth time is 7-14 days.

[0043] The obtained van der Waals misfit layered compound is prepared by a solid-state high-temperature synthesis method and is composed of at least two van der Waals material sublayers. One of the van der Waals material sublayers is a compound layer containing a Group IV or Group V transition metal, and the other van der Waals material sublayer is a compound layer containing a tin, lead, bismuth, antimony, or rare earth metal element. The atoms between the two van der Waals material sublayers are connected by van der Waals forces. The two van der Waals material sublayers are a tetragonal phase layer A and a hexagonal phase layer B, respectively, and form a hetero-superlattice according to the stacking patterns of ABAB and AAB; the crystal structure of the van der Waals misfit layered compound is jointly characterized by Raman spectroscopy and scanning transmission electron microscopy-high angle annular dark field, and contains two-dimensional components with two different lattice constants and shows a staggered arrangement to form a misfit layered structure.

[0044] In addition, the general chemical formula of the van der Waals misfit layered compound is ([MX] 1+δ ) m (TX2) n ; where M is any one of tin, lead, bismuth, antimony, or rare earth metal elements, T is a Group IV or Group V transition metal element, X is a sulfur element or a selenium element, the parameter δ is the in-plane area ratio of the two components, m is the stoichiometric number of the MX layer, and n is the stoichiometric number of the TX2 layer.

[0045] Based on the above content, the van der Waals misfit layered compound is applied to various functional devices based on its electrical properties, specifically including: lateral ferroelectric metal memristors, vertical piezoelectric devices, and superconducting ferroelectric memristive devices.

[0046] Among them, the in-plane ferroelectric tunnel junction of the van der Waals misfit layered compound has a hysteresis current-voltage hysteresis curve with a low threshold voltage, and thus is applied to a lateral ferroelectric metal memristor with low energy consumption. The crystal structure of the van der Waals misfit layered compound has a special crystal structure, specifically: due to the mismatch of the two sublayer lattices, the crystal structure has the characteristic of out-of-plane symmetry breaking and generates deformation along the electric field direction under the action of an electric field, and is applied to a vertical piezoelectric device with efficient electromechanical conversion performance. The van der Waals misfit layered compound is an Ising superconductor with the characteristic of a high upper critical field, and thus remains in a stable superconducting state in a strong magnetic field environment and is applied to a superconducting ferroelectric memristive device with high stability.

[0047] The above content will be further verified by listing specific embodiments below.

[0048] Example 1

[0049] In this example, the preparation of the van der Waals misfit layered compound (SnSe) 1.16 (NbSe2) includes the following steps:

[0050] (1) Weigh tin (Sn, purity 99.99%), niobium (Nb, purity 99.99%) and selenium (Se, purity 99.99%) powders as starting materials, mix them evenly in a ratio of 1.16:1:3.16 to obtain a mixed powder, and the mass of the mixed powder is approximately 1.5 g;

[0051] (2) Use 150 mg of stannous chloride (SnCl2, purity 99.99%) as a transport agent, and co - encapsulate the mixed powder and the transport agent in a vacuum - sealed quartz tube;

[0052] (3) Place the encapsulated quartz tube in a two - temperature - zone furnace, set the temperature at the precursor mixture source end to 900 °C and the temperature at the crystal growth end to 850 °C, and grow for 7 days using chemical vapor transport method to make the mixed powder react and crystallize in the gas - phase environment;

[0053] (4) After the reaction is completed, take out the quartz tube from the two - temperature - zone furnace and perform quenching treatment to cool the crystals in the quartz tube from the reaction temperature to room temperature, fixing the crystal structure, and obtain millimeter - sized, bright black flaky van der Waals misfit - coordinated layered compound (SnSe) 1.16 (NbSe2) single crystal.

[0054] Next, the van der Waals misfit - coordinated layered compound (SnSe) 1.16 (NbSe2) obtained in Example 1 is subjected to combined testing and characterization:

[0055] The crystal structure of the material obtained in Example 1 is characterized by X - ray diffraction spectrum (XRD), and the results are as Figure 2 shown. The XRD pattern shows that all diffractions are (00l) peaks, the diffraction angle range is from 5 to 65 degrees, with a commensurate (002) peak and a small full - width at half - maximum, indicating that the grown (SnSe) 1.16 (NbSe2) single - crystal sample has high quality and good crystallinity.

[0056] The crystal structure of the material obtained in Example 1 is characterized by scanning transmission electron microscopy - high - angle annular dark - field (STEM - HAADF), and the results are as Figure 3 shown. Through the STEM - HAADF image, the microscopic crystal structure of this vdW misfit superlattice (SnSe) 1.16 NbSe2 can be clearly seen. The local atomic structure shows alternating stacked SnSe and NbSe2 heterolayers and two different planar characteristics. The high contrast generated by heavy atoms (such as Nb) provides detailed atomic arrangement information, showing the regular arrangement and distribution of different material layers. And the large range is also a highly ordered alternating hetero - superlattice stacking arrangement, indicating its long - period order.

[0057] The ferroelectricity of the material obtained in Example 1 was characterized by using lateral piezoresponse force microscopy (LPFM), and the results obtained are as Figure 4 shown. At a resonance frequency of 750 kHz, Figure 4 in (a) shows that the local electrical switching polarization spectrum (SS-PFM) exhibits an amplitude butterfly curve and a phase cycling curve with a 180° phase difference within the voltage range from -6 V to 6 V, indicating that the material obtained in Example 1 has in-plane ferroelectric switching hysteresis behavior, demonstrating that there are electrically switchable bistable antiparallel polarization states in (SnSe) 1.16 (NbSe2), and the polarization switching voltages are approximately -0.7 V and +0.6 V. Figure 4 In (b) and Figure 4 in (c) respectively show the in-plane phase and amplitude electric domain patterns in a meander shape of the material obtained in Example 1 after tip-biased polarization at +5 V and -5 V, showing antiparallel remanent polarization with a nearly 180° phase contrast. The lateral piezoresponse force microscopy technique indicates that (SnSe) 1.16 (NbSe2) has in-plane ferroelectricity, which is the basis for its use in lateral ferroelectric metal memristor devices.

[0058] The piezoelectric effect of the material obtained in Example 1 was characterized by using vertical piezoresponse force microscopy (VPFM), and the results obtained are as Figure 5 shown. A voltage of -5 V was applied to a 3×3 μm 2 area, and it was observed that the surface height of the (SnSe) 1.16 (NbSe2) crystal decreased, and then a voltage of +5 V was applied to polarize the central 1×1 μm 2 area, and the surface height of the crystal increased. In the electrostrictive area, its height decreased by 1.3 nm relative to the intrinsic area, while in the electrostrictive elevation area, the height increased by 4.7 nm relative to the original. The vertical piezoresponse force microscopy indicates that (SnSe) 1.16 (NbSe2) has a piezoelectric effect, which is the basis for its use in vertical piezoelectric devices.

[0059] The electronic structure of the material obtained in Example 1 was characterized by using angle-resolved photoemission spectroscopy (ARPES), and the results obtained are as Figure 6 shown. Referring to Figure 6 in (e), (d), (c), (b) and (a), the band dispersion along the Γ-M direction remains basically unchanged when the photon energy changes from 25 eV to 45 eV, indicating that (SnSe) 1.16 (NbSe2) has quasi-two-dimensional electron characteristics.

[0060] Example 2

[0061] In this example, the van der Waals misfit layered compound (SnSe) 1.16(NbSe2)2, comprising the following steps:

[0062] (1) Weigh tin (Sn, purity 99.99%), niobium (Nb, purity 99.99%) and selenium (Se, purity 99.99%) powders as starting materials, mix them evenly in a ratio of 1.16:2:5.16 to obtain a mixed powder, and the mass of the mixed powder is approximately 1.6 g;

[0063] (2) Use 200 mg of stannous bromide (SnBr2, purity 99.99%) as a transport agent, and co-encapsulate the mixed powder and the transport agent in a vacuum-sealed quartz tube;

[0064] (3) Place the encapsulated quartz tube in a two-zone furnace, set the temperature at the source end of the precursor mixture to 900 °C and the temperature at the crystal growth end to 850 °C, and grow for 7 days using chemical vapor transport method to make the mixed powder react and crystallize in the gas phase environment;

[0065] (4) After the reaction is completed, take out the quartz tube from the two-zone furnace and perform quenching treatment to cool the crystals in the quartz tube from the reaction temperature to room temperature, fixing the crystal structure, and obtaining a van der Waals misfit layer compound (SnSe) 1.16 (NbSe2)2 single crystal.

[0066] Example 3

[0067] In this example, the preparation of the van der Waals misfit layer compound (SnSe) 1.17 (NbSe2), comprising the following steps:

[0068] (1) Weigh tin (Sn, purity 99.99%), niobium (Nb, purity 99.99%) and sulfur (S, purity 99.99%) powders as starting materials, mix them evenly in a ratio of 1.17:2:3.17 to obtain a mixed powder, and the mass of the mixed powder is approximately 1.6 g;

[0069] (2) Use 200 mg of stannous chloride (SnCl2, purity 99.99%) as a transport agent, and co-encapsulate the mixed powder and the transport agent in a vacuum-sealed quartz tube;

[0070] (3) Place the encapsulated quartz tube in a two-zone furnace, set the temperature at the source end of the precursor mixture to 850 °C and the temperature at the crystal growth end to 770 °C, and grow for 14 days using chemical vapor transport method to make the mixed powder react and crystallize in the gas phase environment;

[0071] (4) After the reaction is completed, take out the quartz tube from the double-temperature zone furnace and perform quenching treatment to cool the crystals in the quartz tube from the reaction temperature to room temperature, fixing the crystal structure to obtain a van der Waals miscoordinated layered compound (SnSe) with a size of 5 mm. 1.17 (NbSe2) single crystal.

[0072] Example 4

[0073] As Figure 7 shown in (a) and Figure 7 shown in (b) of [reference], prepare the van der Waals miscoordinated layered compound (SnSe) 1.16 (NbSe2) obtained in Example 1 into an in-plane ferroelectric tunnel junction (FTJ) device. Referring to Figure 8 shown in (a) of [reference], scan at different bias voltages to obtain an I-V hysteresis curve graph, which intuitively presents the volt-ampere characteristic behavior of the memristor. As Figure 8 shown in (b) of [reference], at a bias voltage of ±0.3 V, an asymmetric current switch is measured, showing a repetitive reversible behavior between the ON and OFF states, proving that the polarization direction can be effectively adjusted by a small driving voltage, indicating that (SnSe) 1.16 (NbSe2) ferroelectric metal memristor has the advantage of low power consumption.

[0074] Referring to Figure 9 shown in (a) of [reference], prepare the van der Waals miscoordinated layered compound (SnSe) 1.16 (NbSe2) obtained in Example 1 into a piezoelectric device. When the externally applied electric field is opposite to the polarization field of the piezoelectric device material itself, the piezoelectric device material stretches, and when the externally applied electric field is in the same direction as the polarization field of the piezoelectric device material itself, the piezoelectric device material compresses. As Figure 9 shown in (b) of [reference], when applying alternating currents with different amplitudes, the piezoelectric amplitude of the piezoelectric device increases linearly with the amplitude of the alternating current.

[0075] Therefore, by adopting the above method for synthesizing van der Waals miscoordinated layered compounds based on solid-state high temperature and its application, the problems of complex process, low efficiency and high cost in the traditional preparation of van der Waals miscoordinated layered compounds are solved, a functional device application regulation system is constructed, its wide application in multiple fields is realized, and a new direction is provided for the future development of science and technology.

[0076] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. For the same or similar parts among the various embodiments, reference can be made to each other.

[0077] In this text, specific examples are used to elaborate on the principles and implementation manners of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manners and application scopes. To sum up, the content of this specification should not be construed as a limitation on the present invention.

Claims

1. A van der Waals misaligned layered compound based on solid-state high-temperature synthesis, characterized in that, The van der Waals misfit layered compound is prepared by a solid-state high-temperature synthesis method and is composed of at least two van der Waals material sublayers. One of the van der Waals material sublayers is a NbSe2 compound layer containing the Group V transition metal niobium, and the other van der Waals material sublayer is a SnSe compound layer containing the Group IV metal tin. The atoms of the two van der Waals material sublayers are connected by van der Waals forces to form a van der Waals misfit layered compound with the chemical formula (SnSe) 1.16 (NbSe2); The two van der Waals material sublayers are a tetragonal phase layer A and a hexagonal phase layer B respectively, and form a heterostructure superlattice according to the ABAB stacking mode; the crystal structure of the van der Waals misfit layer compound is jointly characterized by Raman spectroscopy and scanning transmission electron microscopy-high angle annular dark field, and contains two-dimensional components with two different lattice constants, and is arranged in a staggered manner to form a misfit layer structure.

2. A preparation method of a van der Waals misaligned layered compound based on solid-state high-temperature synthesis according to claim 1, characterized in that, It includes the following steps: According to the chemical formula of the target compound, weigh elemental powder of each element as the starting material, and mix evenly to obtain a mixed powder; Seal the mixed powder and the transport agent together in a vacuum-sealed quartz tube; wherein, the transport agent is a stannous halide compound, and the stannous halide compound is one of stannous chloride and stannous bromide; Place the sealed quartz tube in a two-temperature zone furnace, and set the temperatures of the precursor mixture source end and the crystal growth end. Use chemical vapor transport to react and crystallize the mixed powder in a gas-phase environment; wherein, the temperature range of the precursor mixture source end is 800-900 °C; the temperature range of the crystal growth end is 750-850 °C; use chemical vapor transport to grow crystals, and the growth time is 7-14 days; After the reaction is completed, take out the quartz tube from the two-temperature zone furnace and perform quenching treatment to cool the crystals in the quartz tube from the reaction temperature to room temperature, fix the crystal structure, and obtain a single crystal of the van der Waals misfit layer compound, that is, obtain the van der Waals misfit layer compound.

3. An application of the van der Waals misaligned layered compound based on solid-state high-temperature synthesis according to claim 1, characterized in that, Based on the electrical properties of the van der Waals misfit layer compound, it is applied to a variety of functional devices, specifically including: lateral ferroelectric metal memristors, vertical piezoelectric devices, and superconducting ferroelectric memristor devices.

4. The application of a van der Waals misaligned layered compound based on solid-state high-temperature synthesis according to claim 3, characterized in that, The in-plane ferroelectric tunnel junction of the van der Waals misfit layer compound has a hysteresis current-voltage hysteresis curve with a low threshold voltage, and is thus applied to a lateral ferroelectric metal memristor with low energy consumption.

5. The application of a van der Waals misaligned layered compound based on solid-state high-temperature synthesis according to claim 3, wherein The crystal structure of the van der Waals misfit layer compound has the characteristic of out-of-plane symmetry breaking due to the mismatch of the two sublayer lattices, and deforms along the electric field direction under the action of an electric field, and is applied to a vertical piezoelectric device with high-efficiency electromechanical conversion performance.

6. The application of a van der Waals misaligned layered compound based on solid-state high-temperature synthesis according to claim 3, wherein The van der Waals misfit layer compound is an Ising superconductor with the characteristic of a high upper critical field, and thus remains in a stable superconducting state in a strong magnetic field environment, and is applied to a superconducting ferroelectric memristor device with high stability.

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