Monoclinic crystal system crystal material and preparation method thereof

Abstract

The invention discloses a monoclinic structure TiSe3 crystal and a preparation method thereof, and belongs to the technical field of new material preparation, the cell parameter of the crystal is # imgabs0 # beta = 98.10 (2) degrees, and the space group of the crystal is P21 / m. According to the method, elementary substance titanium and selenium are used as raw materials, the monoclinic phase TiSe3 crystal is finally prepared through the technological processes of mixing, briquetting, assembling, high-temperature and high-pressure synthesis and cooling pressure relief, the atomic percent of the Ti element is 25.4-25.7%, the atomic percent of the Se element is 74.6-74.3%, the preparation method is simple, the preparation period is short, it is proved that the TiSe3 crystal is of a single phase and is free of impurities and twin crystals, and the method is suitable for industrial production. In addition, the crystal shows a semiconductor conductive behavior, so that a sample can be used as a base material of a semiconductor device, the band gap of the sample is similar to that of a known superior semiconductor material, and the crystal has a good semiconductor application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of new material preparation, and in particular to a monoclinic crystal material and a preparation method thereof. Technical Background

[0002] With the continuous advancement of science and technology, the carrier of information transmission is developing from traditional electrons to optoelectronics and photons. In two-dimensional materials, carriers are restricted to move on a two-dimensional scale, which makes two-dimensional materials exhibit special physical and chemical properties. From the perspective of the crystal structure of the material, semiconductor materials are also gradually changing from traditional three-dimensional materials to thin layers and two-dimensional super-wave layers. Researchers' extensive attention to two-dimensional materials stems from the successful separation of stable thin layers of graphene by scientists at the University of Manchester in 2004. In addition, two-dimensional materials are bonded by van der Waals bonds, which are easy to peel off and can be combined with other two-dimensional materials in a variety of ways like Lego blocks to form a series of van der Waals heterojunctions with different properties. The unique crystal and electronic structure of two-dimensional materials provides a material basis for the development of energy storage and conversion, catalysis, electronics, biomedicine, sensors and other fields.

[0003] So far, the most widely studied layered semiconductor materials are transition metal dichalcogenides (MoS 2 , MoSe 2 , WS 2 and WSe 2 ). These materials have many advantages of layered materials. Only a part of the broader family of two-dimensional layered materials has been explored so far, so there are still many unknown new two-dimensional layered materials that deserve further exploration by researchers. Transition metal trichalcogenides have the characteristics of transition metal dichalcogenides layered structure, and also show richer quasi-one-dimensional material properties. For example, the optoelectronic properties have strong anisotropy.

[0004] After researching ZrSe 3 and HfSe 3 All have the same crystal symmetry (monoclinic system, space group: P2 1 / m), and they are all semiconductors. The research found that the highest chemical ratio of Se in the Ti-Se compound prepared at normal pressure and high temperature is 1:2, and TiSe 2 It is a non-magnetic metal material with much narrower application prospects than semiconductor materials. Therefore, this application aims to develop a TiSe 3 Crystals, and a monoclinic TiSe was synthesized for the first time by high temperature and high pressure method on a Kawai type large cavity press. 3 Semiconductor materials. Summary of the invention

[0005] In view of the deficiencies of the prior art, an object of the present invention is to provide a monoclinic crystal material and a preparation method thereof.

[0006] To achieve the above-mentioned and other related purposes, the first aspect of the present invention provides a monoclinic crystal material, wherein the molecular formula of the crystal is TiSe 3 , the TiSe 3 The unit cell parameters are: beta = 98.10 (2) °; the space group of the crystal is P2 1 / m.

[0007] A second aspect of the present invention provides a method for preparing a monoclinic crystal material, the method comprising the following steps:

[0008] S1, grinding and tableting elemental titanium and selenium, and then wrapping them with a hexagonal boron nitride protective cover to prepare an inclusion;

[0009] S2. React the inclusions described in step S1 at a pressure of 5 to 6 GPa and 850 to 950° C. to prepare a monoclinic crystal material.

[0010] In some embodiments of the present invention, the molar ratio of the elemental titanium to selenium is 1:3 to 3.5.

[0011] In some embodiments of the present invention, in step S1, elemental titanium and selenium are ground and pressed into a cylindrical shape;

[0012] Preferably, the cylinder has a diameter of 2.5 to 4.5 mm and a height of 2 to 5 mm.

[0013] More preferably, the cylinder has a diameter of 3.5 mm and a height of 4 mm.

[0014] In some embodiments of the present invention, in step S1, the hexagonal boron nitride protective cover is a hexagonal boron nitride tube and a hexagonal boron nitride sheet for sealing the hexagonal boron nitride tube.

[0015] Preferably, the wall thickness of the hexagonal boron nitride tube is 0.15-0.35 mm, and the inner diameter is 2.5-4.5 mm; the thickness of the hexagonal boron nitride sheet is 0.25-0.75 mm, and the inner diameter is 3-5 mm. More preferably, the wall thickness of the hexagonal boron nitride tube is 0.25 mm, and the inner diameter is 3.5 mm; the thickness of the hexagonal boron nitride sheet is 0.5 mm, and the inner diameter is 4 mm.

[0016] In some embodiments of the present invention, in step S2, the inclusion is placed in a graphite heating furnace and then loaded into a high-pressure assembly, and finally the high-pressure assembly is placed in a high-pressure reactor for reaction; preferably, the high-pressure reactor is a large-cavity press.

[0017] In some embodiments of the present invention, step S2 includes the following steps:

[0018] S21, start the pressurization procedure, and increase the pressure to 5-6 GPa at a pressurization rate of 90-110 tons / hour;

[0019] S22, start the heating program, raise the temperature to 850-950°C, and keep it warm for 2-3h;

[0020] S23, cooling the reactants at a rate of 60 to 100° C. per hour to slowly cool the reactants to 650 to 750° C.;

[0021] S24. Quench to room temperature and slowly release the pressure to normal pressure.

[0022] The third aspect of the present invention provides a monoclinic crystal material prepared by any of the above preparation methods.

[0023] A fourth aspect of the present invention provides a use of the above-mentioned monoclinic crystal material in a semiconductor device.

[0024] The beneficial effects of the present invention are further illustrated below in conjunction with embodiments.

[0025] In order to make the invention purpose, technical scheme and beneficial technical effect of the present invention clearer, the present invention is further described in detail below in conjunction with examples. However, it should be understood that the examples of the present invention are only for explaining the present invention, not for limiting the present invention, and the examples of the present invention are not limited to the examples given in the specification. The specific experimental conditions or operating conditions not specified in the examples are made under conventional conditions, or are made under the conditions recommended by the material supplier.

[0026] In addition, it should be understood that one or more method steps mentioned in the present invention do not exclude the existence of other method steps before or after the combination step or the insertion of other method steps between these explicitly mentioned steps, unless otherwise specified; unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or to define the scope of implementation of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of implementation of the present invention without substantially changing the technical content. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the device for synthesizing samples at high temperature and high pressure of the present invention.

[0028] Figure 2 TiSe of the present invention 3 Optical photographs of samples and geometric dimensions.

[0029] Figure 3 The TiSe 3 Energy dispersive X-ray spectrum of the samples.

[0030] Figure 4 The TiSe 3 X-ray diffraction pattern of single crystal sample.

[0031] Figure 5 The simple monoclinic TiSe 3 Schematic representation of the crystal structure along different crystallographic axes.

[0032] Figure 6 The sample TiSe of the present invention 3 The resistance-temperature curve.

[0033] Figure 7 The sample TiSe of the present invention 3 UV absorption spectrum and band gap analysis. DETAILED DESCRIPTION

[0034] The applicant of the present invention investigated the Ti-Se binary phase diagram and found that in the order of increasing Se content, the Ti-Se binary phase diagram has the following phases: TiSe (space: Pnma, lattice parameters: a = 0.6222nm, b = 0.3494nm, c = 0.6462nm), Ti 3 Se 4 (space group: C2 / m, a=1.3650nm, b=0.3570nm, c=0.6360nm, β=117.5°), Ti 2 Se 3 (space group: P-31c, a=b=0.6233nm, c=1.1984nm), TiSe 2 (Space group: P-3m1, a=b=0.3540nm, c=0.6008nm). Through the above research results, we can find that the chemical ratio of Se in the Ti-Se compound prepared at normal pressure and high temperature is up to 1:2, which is a non-magnetic metal material. Titanium (Ti), zirconium (Zr) and hafnium (Hf) are three transition metals of group IV with similar electronic configurations. By investigating the database, we found that ZrSe can be prepared by normal pressure and high temperature method. 3 and HfSe 3 In addition, ZrSe 3 and HfSe 3 All have the same crystal symmetry (monoclinic system, space group: P2 1 / m), and both compounds are semiconductors. Therefore, TiSe is prepared by a special material growth method. 3The high temperature and high pressure method is a relatively mature sample preparation technology at present, and it plays a unique role in material preparation. For example, it can expand the chemical matching degree of material synthesis. The applicant has recently successfully prepared monoclinic TiSe by high temperature and high pressure method. 3 , expanding the phase range of the Ti-Se binary phase diagram. And after a large number of experiments, it was found that the synthesis method of suitable high temperature and high pressure assembly can prepare TiSe with a monoclinic structure. 3 Semiconductor materials. The large cavity press has the advantages of physical mechanical pressurization, eight-sided wrapping of magnesium oxide and pyrophyllite sealing, which can provide a sealed and high-strength sample cavity for the sample. The physical pressure provided by the large cavity press is much greater than the vapor pressure of the sample at high temperature. Therefore, the large cavity press is very suitable for sealing chemical reactants that are easily oxidized or easily volatilized at high temperatures, plays an extremely important role in the research and exploration of new materials, and is an important means for preparing triselenium compounds. The present invention uses a high temperature and high pressure method on a 2000-ton Kawai type large cavity press to synthesize a TiSe with a monoclinic structure for the first time. 3 Single crystal sample. On this basis, the present invention is completed.

[0035] The first aspect of the present invention provides a monoclinic crystal material, wherein the molecular formula of the crystal is TiSe 3 ; The unit cell parameters of the crystal are beta = 98.10 (2) degrees; the space group of the crystal is P2 1 / m.

[0036] The testing and single crystal analysis methods are as follows: In the monoclinic crystal form provided by the present invention, there is no special limitation on the determination of single crystal data, and single crystal testing instruments known to those skilled in the art can be used.

[0037] In a specific embodiment, the single crystal data of the monoclinic crystal form is collected on a Bruker D8 Venture dual-target small molecule X-ray single crystal diffractometer at 150K for the single crystal X-ray diffraction data of the orthorhombic crystal form, wherein the Mo Kα radiation When collecting data, the single crystal diffractometer tube voltage was 50 kV and the tube current was 30 mA. ShelXT 2018 / 3 (Sheldrick, 2018) was used to analyze the crystal structure, the least squares method was used to correct the structural parameters and identify the atomic types, and the geometric calculation method and the difference Fourier method were used to obtain the positions of all atoms. The final reliability factor R 1 =0.1239,wR 2 =0.3274, goodness factor (Goodness~of~fit on F 2 )=1.287.

[0038] The molecular formula of the crystal of the present invention is further determined by energy dispersion spectrum analysis, and the molecular formula is TiSe 3 .

[0039] The second aspect of the present invention provides a method for preparing a monoclinic crystal material, the method comprising the following steps:

[0040] S1, mixing elemental titanium and selenium, grinding and tableting, and then wrapping with a hexagonal boron nitride protective cover to prepare an inclusion;

[0041] S2. React the inclusions described in step S1 at a pressure of 5 to 6 GPa and 850 to 950° C. to prepare a monoclinic crystal material.

[0042] In the preparation method of the monoclinic crystal material provided by the present invention, in step S1, under inert gas protection conditions (specifically, an optional glove box argon environment), elemental titanium and selenium are mixed in a suitable molar ratio, and ground in a mortar such as agate for 30 minutes, the uniformly mixed powder is loaded into a stainless steel mold (powder tablet press), pressurized to 8MPa, and the mixed powder is pressed into a cylindrical shape with a diameter of 2.5 to 4.5mm and a height of 2 to 5mm. In some embodiments, the diameter of the cylinder is 2.5 to 3.0mm, 3.0 to 3.5mm, 3.5 to 4.0mm or 4.0 to 4.5mm, etc. The height of the cylinder is 2.0 to 3.0mm, 3.0 to 3.5mm, 3.5 to 4.0mm or 4.0 to 4.5mm, etc. In some embodiments, the molar ratio of elemental titanium to selenium is 1:3, 1:3.5, etc., preferably 1:3, and when the molar ratio of elemental titanium to selenium is 1:3, the sample quality obtained is the best.

[0043] Since selenium reacts with both precious metals gold and platinum under high temperature and high pressure, unlike the samples wrapped with precious metals in the existing high temperature and high pressure experiments, the sample reactants in the present invention are wrapped with hexagonal boron nitride, which is resistant to high temperature and high pressure and has stable chemical properties. The hexagonal boron nitride material is resistant to high temperature and high pressure and has stable chemical properties, which can reduce the probability of generating impurities. In the present invention, a cylindrical sample is placed in a hexagonal boron nitride tube, and both ends of the tube are covered with hexagonal boron nitride discs to form an inclusion wrapped by a hexagonal boron nitride protective sleeve. In some embodiments, the hexagonal boron nitride tube is hollow and open at both ends, and its cross-section is circular; the wall thickness of the hexagonal boron nitride tube is 0.15 to 0.35 mm, and the inner diameter is 2.5 to 4.5 mm. Preferably, the wall thickness is 0.25 mm and the inner diameter is 3.5 mm. The thickness of the hexagonal boron nitride sheet is 0.25 to 0.75 mm, and the inner diameter is 3 to 5 mm. Preferably, the thickness is 0.5 mm and the inner diameter is 4 mm.

[0044] In step S2 of the method for preparing the monoclinic crystal material provided by the present invention, the inclusion is placed in a graphite heating furnace and then loaded into a high-pressure assembly. The high-pressure assembly is a multi-layer cylindrical structure, that is, cylindrical assemblies of different materials and functions are assembled in a certain order. Specifically, the sample is first wrapped with hexagonal boron nitride, then wrapped with graphite, and the outer layer is wrapped with zirconium oxide and magnesium oxide octahedron is placed in it to form a complete assembly. The assembly drawing is as shown in FIG. Figure 1 Then the assembly is placed in a high pressure reactor for reaction, and the specific steps are as follows:

[0045] S21, start the pressurization program, increase the pressure to 5-6 GPa at a pressurization rate of 90-110 tons / hour, and the pressurization rate can be selected from 80-90 tons / hour, 90-100 tons / hour, 100-110 tons / hour, 110-120 tons / hour;

[0046] S22, start the heating program, raise the temperature to 850-950°C, and keep it warm for 2-3h; optionally, raise the temperature to 850-900°C, 900-950°C;

[0047] S23, cooling the reactants slowly to 650-750°C at a rate of 60-100°C per hour; optionally, cooling the reactants slowly to 650-700°C, 700-750°C at a rate of 60-70°C, 70-80°C, 80-90°C, 90-100°C per hour;

[0048] In a preferred embodiment, the pressurization rate in step S21 is 100 tons / hour, and the pressure is increased to 5 GPa. In step S22, the temperature is raised to 900°C and kept for 2 hours. In step S23, the temperature is lowered at a rate of 60°C per hour to reduce the temperature of the reactants to 700°C.

[0049] In a preferred embodiment, the pressurization rate in step S21 is 100 tons / hour, and the pressure is increased to 5 GPa. In step S22, the temperature is raised to 850°C and kept for 3 hours. In step S23, the temperature is lowered at a rate of 100°C per hour to reduce the temperature of the reactants to 650°C.

[0050] In a preferred embodiment, the pressurization rate in step S21 is 100 tons / hour, and the pressure is increased to 6 GPa. In step S22, the temperature is raised to 950°C and kept for 3 hours. In step S23, the temperature is lowered at a rate of 100°C per hour to reduce the temperature of the reactants to 750°C.

[0051] S24, quench to room temperature, slowly release the pressure to normal pressure. Take out the sample from the magnesium oxide octahedron.

[0052] In some embodiments, the high-pressure reactor uses a large-cavity press, more specifically a 2,000-ton Kawai-type large-cavity press. It should be further explained that, in step S2, pressure and temperature are calibrated before the reaction; the pressure is calibrated using the resistance-pressure curve of metal Bi; the temperature is calibrated by the crystal structure phase change of silicon dioxide. The heating temperature is controlled by controlling the heating power, and the temperature is measured by a tungsten-rhenium thermocouple.

[0053] There are two kinds of pressure in the large cavity press. The oil pressure generated by the external oil pump is used as the driving pressure. The oil pressure acts on the cavity and is then transmitted to the octahedron assembly and the sample, generating the pressure felt by the sample. There is an approximately linear correspondence between these two pressures. The experimenter can control the oil pressure, so measuring the relationship between the two pressures can guide us to get the required pressure felt by the sample. The resistance-pressure curve calibration pressure of metal Bi is specifically: according to the change point of the high-voltage resistance of metal Bi at 2.55GPa and 7.7GPa, the corresponding oil pressure value is recorded, and the corresponding relationship between the thrust of the large press and the pressure in the sample cavity can be calibrated.

[0054] The beneficial effects of the present invention are as follows:

[0055] 1) The present invention prepares a monoclinic crystal material under high temperature and high pressure conditions. The synthesis method is simple and the preparation cycle is short. In addition, the sealing assembly of the present invention isolates the pre-pressed titanium-selenium mixture from the air, realizes the pure binary reaction under high temperature and high pressure conditions, and prepares TiSe 3 The single crystal structure of the monoclinic system has good crystal quality and is confirmed to be a single phase by single crystal X-ray diffraction. There are no impurities or twins in the sample.

[0056] 2) The single crystal material of the present invention has an increased resistance as the temperature decreases, showing semiconductor conductive behavior, indicating that the sample can be used as a substrate for semiconductor devices.

[0057] 3) The single crystal material of the present invention has a band gap of 1.7 to 1.8 eV. A band gap that is too large or too small will result in poor or unstable electrical properties. The band gap of the single crystal material of the present invention is similar to that of known superior semiconductor materials, and has good semiconductor application prospects.

[0058] Example 1

[0059] 1) A cylindrical mixture of titanium and selenium is prepared under normal pressure.

[0060] Chemically pure elemental titanium and selenium were mixed evenly in a glove box (argon environment) at a molar ratio of 1:3 and mortared in an agate mortar for half an hour. The reactant powder was pressed into a cylinder with a height of 4.0 mm and a diameter of 3.5 mm by a powder tablet press (pressure: 8 MPa). In order to ensure a pure reaction environment, hexagonal boron nitride tubes (wall thickness: 0.25 mm, inner diameter: 3.5 mm) and hexagonal boron nitride discs (thickness: 0.5 mm, diameter 4 mm) that are resistant to high temperature and high pressure and have stable chemical properties were selected for packaging to reduce the probability of generating impurities.

[0061] 2) The cylindrical sample and the hexagonal boron nitride protective sleeve are placed together in a high-voltage assembly.

[0062] First, place the cylindrical sample reactant and the hexagonal boron nitride protective sleeve into a graphite heating furnace. Then place the sample into a high-pressure assembly for high-pressure and high-temperature synthesis (see the assembly drawing for details). Figure 1 ).

[0063] 3) The samples were synthesized on a 2000-ton Kawai-type large-cavity press.

[0064] The sample synthesis is carried out on a Kawai type large-cavity press with a thrust of 2000 tons. First, the pressure is slowly increased to 5GPa (100 tons per hour) at room temperature, and then the heating program is started to heat to 900°C, and then kept warm for two hours under high temperature and high pressure conditions (5GPa+900°C). In order to prepare single crystal samples, it is necessary to anneal the samples under high temperature and high pressure. The method is to cool down the sample at a rate of 1°C / minute and slowly cool the temperature of the sample to 700°C. Finally, turn off the heating power and quickly quench the sample to room temperature. After the temperature drops to room temperature, slowly release the pressure in the sample chamber (25 tons per hour) to normal pressure. Take out the sample from the magnesium oxide octahedron. Under the microscope, you can see that the sample is gray-black, elongated crystals (see Figure 2 )

[0065] Representation 1

[0066] The samples obtained after quenching were subjected to single crystal X-ray diffraction analysis. The instrument used was a Bruker D8 Venture dual-target small molecule X-ray single crystal diffractometer. The single crystal X-ray diffraction data of orthorhombic crystals were collected at 150 K, with Mo Kα radiation. When collecting data, the single crystal diffractometer tube voltage was 50 kV and the tube current was 30 mA. ShelXT 2018 / 3 (Sheldrick, 2018) was used to analyze the crystal structure, the least squares method was used to correct the structural parameters and identify the atomic types, and the geometric calculation method and the difference Fourier method were used to obtain the positions of all atoms. The final reliability factor R 1 =0.1239,wR 2=0.3274, goodness factor (Goodness~of~fit on F 2 )=1.287. The final chemical formula of the sample was determined to be TiSe 3 The calculated molecular weight is 284.78 and the crystal density of the material is 5.554 g / cm 3 .

[0067] The crystallographic information file of the sample was obtained by single crystal analysis software. The lattice parameters are: space group: P2 1 / m, the unit cell parameters are: beta = 98.10 (2) °. Based on the analyzed crystallographic information file, see Table 1 to draw the monoclinic TiSe 3 Schematic diagram of the crystal structure (see Figure 2 ).

[0068] Table 1 Crystal data and structure refinement of TiSe3 (150K)

[0069]

[0070]

[0071] In addition, the diffraction points of the single crystal sample in three directions of reciprocal space are as follows: Figure 4 As shown, the single crystal diffraction points are small and bright, without tailing or connection, indicating that the single crystal phase quality is high and there are no impurities or twins in the single crystal sample.

[0072] Representation 2

[0073] The chemical composition of the samples obtained after quenching was analyzed by energy dispersive X-ray spectroscopy (test conditions: area size: 224 μm, voltage, 15 KV, point detector (BSD Full)). Figure 3 The EDX spectrum analysis diagram of the sample, the element analysis is shown in Table 2, the proportion of titanium is 25.49%, the proportion of selenium is 74.51%, because the atomic weight of selenium (78.96) is larger than that of titanium (47.867), the chemical ratio of titanium to selenium is close to 1:3, the energy dispersive X-ray spectrum analysis (EDX) result is consistent with the single crystal structure analysis result of the present invention, and the chemical formula of the sample is certified to be TiSe 3 .

[0074] Based on the analyzed crystallographic information file, a simple monoclinic TiSe 3 Schematic diagram of the crystal structure of Figure 5 shown. Figure 5(a) and 5(b) are schematic diagrams of the crystal structure of the sample along different crystal directions. The black atoms are Ti, the gray atoms are Se, and there are 8 Se atoms around each Ti. Figure 5 As shown in a, TiSe 3 The polyhedrons form a layered structure along the ac planes and are stacked in the b-axis direction; Figure 5 b is TiSe 3 Schematic diagram of the crystal along the b-axis, forming a one-dimensional infinite chain along the b-axis. The layered and one-dimensional infinite chain indicates that the chemical bonds of the material are different along different crystal directions, which leads to the physical properties of the material showing differences in different crystallographic axes, that is, anisotropy. That is, the monoclinic TiSe of this application 3 It is a quasi-one-dimensional or two-dimensional material in crystal structure, that is, the physical properties parallel to the crystal layer are different from those perpendicular to the crystal layer. Because the layers are connected by van der Waals bonds, the spacing is large and the binding energy is small, while the layers are connected by covalent bonds or metallic bonds, the spacing is small and the binding energy is large, so it is very suitable for use in thin films or electronic devices.

[0075] Table 2 Atomic percentage of chemical elements of samples of the present invention

[0076]

[0077]

[0078] Example 2

[0079] 1) A cylindrical reactant of titanium and selenium is prepared under normal pressure.

[0080] Chemically pure elemental titanium and selenium were mixed evenly in a glove box (argon environment) at a molar ratio of 1:3 and mortared in an agate mortar for half an hour. The reactant powder was pressed into a cylinder with a height of 4.0 mm and a diameter of 3.5 mm by a powder tablet press (pressure: 8 MPa). In order to ensure a pure reaction environment, hexagonal boron nitride tubes (wall thickness: 0.25 mm, inner diameter: 3.5 mm) and hexagonal boron nitride discs (thickness: 0.5 mm, diameter 4 mm) that are resistant to high temperature and high pressure and have stable chemical properties were selected for packaging to reduce the probability of generating impurities.

[0081] 2) The cylindrical sample and the hexagonal boron nitride protective sleeve are placed together in a high-voltage assembly.

[0082] First, place the cylindrical sample reactant and the hexagonal boron nitride protective sleeve into a graphite heating furnace. Then place the sample into a high-pressure assembly for high-pressure and high-temperature synthesis (see assembly drawing for details). Figure 1 ).

[0083] 3) The samples were synthesized on a 2000-ton Kawai-type large-cavity press.

[0084] The sample synthesis was carried out on a Kawai type large cavity press with a thrust of 2000 tons. First, the pressure was slowly increased (100 tons per hour) to 5GPa at room temperature, and then the heating program was started to heat to 850℃. It was kept warm for 3 hours under high temperature and high pressure conditions (5GPa+850℃), and then cooled at a rate of 100℃ per hour to slowly cool the sample temperature to 650℃. Then the power was turned off to quench the sample to room temperature. Finally, the pressure was slowly unloaded (25 tons per hour) to normal pressure. After taking the sample out of the magnesium oxide octahedron, a shiny single crystal sample can be seen.

[0085] Similar to Example 1, the sample obtained after quenching also has a single crystal semiconductor with a monoclinic structure. Single crystal X-ray diffraction, EDX and ultraviolet absorption spectrum analysis are performed on it, and it is found that the sample has a monoclinic semiconductor.

[0086] Example 3

[0087] 1) Preparation of cylindrical reactants of titanium and selenium under normal pressure

[0088] Chemically pure elemental titanium and selenium were mixed evenly in a glove box at a molar ratio of 1:3.5, and mortared in an agate mortar for half an hour. The reactant powder was pressed into a cylinder with a height of 4.0 mm and a diameter of 3.5 mm by a powder tablet press (pressure: 8 MPa). Since selenium reacts with both precious metals gold and platinum under high temperature and high pressure, the sample reactant in the present invention is wrapped with hexagonal boron nitride that is resistant to high temperature and high pressure and has stable chemical properties, which reduces the probability of generating impurities. The excess selenium acts as a flux.

[0089] 2) The cylindrical sample and the hexagonal boron nitride protective sleeve are placed together in a high-voltage assembly.

[0090] First, place the cylindrical sample reactant and the hexagonal boron nitride protective sleeve into a graphite heating furnace. Then place the sample into a high-pressure assembly for high-pressure and high-temperature synthesis (see assembly drawing for details). Figure 1 ).

[0091] 3) The samples were synthesized on a 2000-ton Kawai-type large-cavity press.

[0092] The sample synthesis was carried out on a Kawai type large cavity press with a thrust of 2000 tons. First, the pressure was slowly increased to 6GPa at room temperature, and then the heating program was started to heat to 950℃, and then kept at high temperature and high pressure for 3 hours, and then cooled at a rate of 100℃ per hour, the temperature of the sample was slowly cooled to 750℃, and then quenched to room temperature, and finally slowly decompressed to normal pressure.

[0093] Similar to Example 1, the sample obtained after quenching also has a monoclinic semiconductor single crystal. A single crystal X-ray diffraction study was performed on it, and it was found that the sample has a monoclinic crystal.

[0094] The performance of the samples is tested through the optical property measurement system, including the relationship between resistance strength and temperature. The optical properties and application prospects of the samples are analyzed through the UV-visible light spectrum and band gap of the samples.

[0095] Experimental Example 1

[0096] The test method of the single product prepared by the present invention is as follows:

[0097] 1) The instrument used for the resistance-temperature curve test is the Physical Property Measurement System (PPMS) produced by Quantum Design, an American company. Currently, PPMS is widely used in international and domestic universities and research institutes to characterize the electrical conductivity and thermal conductivity of materials. The test parameters of the resistance-temperature curve are a temperature range of 2K-300K, no magnetic field, and an applied current of 0.1 mA.

[0098] The TiSe 3 The sample was tested for resistance-temperature curve, and the experimental results are as follows Figure 6 As shown, TiSe 3 The resistance of TiSe increases with decreasing temperature, indicating that 3 The sample exhibits semiconductor conductive behavior.

[0099] 2) The instrument used for UV-visible spectrum test is a high-pressure, low-temperature, room-temperature micro-area near-infrared transmissive-reflective steady-state fluorescence spectrum system manufactured by Shanghai Fuxiang Optics Co., Ltd. The wavelength range is 280nm-1700nm, the test temperature is 300K, the test mode is transmission mode, and UV-visible absorption spectroscopy is a conventional technical method currently used by international and domestic researchers to test the band gap of semiconductor materials.

[0100] The TiSe 3 Sample test UV-visible spectrum and bandgap analysis, analysis results Figure 7 As shown, the analysis results show that the band gap of the sample of the present invention is 1.75eV. HfSe with the same crystal structure 3 Band gap is 1.0eV, ZrSe 3 The band gap of TiS is 1.1-1.3eV. 3 Band gap is 0.8-1.1eV, HfS 3 Band gap is 1.7-3.1eV, ZrS 3 The band gap of TiTe is 1.9-2.8eV.3 The band gap of HfTe is 0.69eV. 3 and ZrTe 3 It is metal.

Claims

1. A monoclinic crystal material, the molecular formula of the crystal is TiSe3; The unit cell parameters of the crystal are beta = 98.10(2)°; The space group of the crystal is P21 / m.

2. The monoclinic crystal material according to claim 1, characterized in that: The atomic percentage of the Ti element in the monoclinic crystal material is 25.4-25.7%, and the atomic percentage of the Se element is 74.6-74.3%.

3. The monoclinic crystal material according to claim 1, characterized in that: The resistance of the monoclinic crystal material increases as the temperature decreases; And / or, the band gap of the monoclinic crystal material is 1.7 to 1.8 eV.

4. A method for preparing a monoclinic crystal material, characterized in that: The method comprises the following steps: S1. Grinding and tableting elemental titanium and selenium, and then wrapping them with a hexagonal boron nitride protective cover to prepare an inclusion; the molar ratio of elemental titanium to selenium is 1:3-3.5; S2. React the inclusions described in step S1 at a pressure of 5 to 6 GPa and 850 to 950° C. to prepare a monoclinic crystal material.

5. The method for preparing a monoclinic crystal material according to claim 4, characterized in that: In the step S1, the elemental titanium and selenium are ground and pressed into a cylinder; Preferably, the cylinder has a diameter of 2.5 to 4.5 mm and a height of 2 to 5 mm.

6. The method for preparing a monoclinic crystal material according to claim 4, characterized in that: In the step S1, the hexagonal boron nitride protective cover is a hexagonal boron nitride tube and a hexagonal boron nitride sheet for sealing the hexagonal boron nitride tube; Preferably, the wall thickness of the hexagonal boron nitride tube is 0.15-0.35 mm, and the inner diameter is 2.5-4.5 mm; the thickness of the hexagonal boron nitride sheet is 0.25-0.75 mm, and the inner diameter is 3-5 mm.

7. The method for preparing a monoclinic crystal material according to claim 4, characterized in that: In the step S2, the inclusion is placed in a graphite heating furnace and then loaded into a high-pressure assembly, and finally the high-pressure assembly is placed in a high-pressure reactor for reaction; Preferably, the high pressure reactor is a large cavity press.

8. The method for preparing the monoclinic crystal material according to claim 7, characterized in that: In the step S2, the reaction comprises the following steps: S21, start the pressurization procedure, and increase the pressure to 5-6 GPa at a pressurization rate of 90-110 tons / hour; S22, start the heating program, raise the temperature to 850-950°C, and keep it warm for 2-3h; S23, cooling the reactants at a rate of 60 to 100° C. per hour to slowly cool the reactants to 650 to 750° C.; S24. Quench to room temperature and slowly release the pressure to normal pressure.

9. A monoclinic crystal material prepared by the method according to any one of claims 4 to 8.

10. Use of a monoclinic crystal material according to claim 1 and / or 9 in a semiconductor device.

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