CN114438592B - Monoclinic system crystal form substance and preparation method thereof - Google Patents
Monoclinic system crystal form substance and preparation method thereof Download PDFInfo
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Abstract
The invention relates to the technical field of new material preparation, in particular to a monoclinic crystal type substance and a preparation method thereof. The molecular formula of the monoclinic system crystal form substance is MoP 2 (ii) a The monoclinic crystal type substance comprises the following unit cell parameters
α＝90°，β＝119.192±0.006°，γ＝90°，
The crystal form space group is C2/m, and the crystal system belongs to a monoclinic system. The method utilizes the conditions of high temperature and high pressure, can overcome the limitation that the vapor pressure of red phosphorus is high and is easy to cause tube explosion of a quartz tube, thereby preparing the MoP with a monoclinic structure at the bottom core 2 The single crystal has good crystallization quality, is single-phase through single crystal X-ray diffraction, and has no impurity and goldenrain crystal in the single crystal.
Description
Technical Field
The invention relates to the technical field of new material preparation, in particular to a monoclinic crystal system crystal form substance and a preparation method thereof.
Background
In recent years, metal phosphorus-rich compounds TPn (T is metal, and n has a value of 2, 2.5, 3, 4, etc.) have attracted extensive research interests of researchers due to their abundant crystal structure types and novel physicochemical properties. TP (TP) 2 Is an important system in metal phosphorus-rich compounds. In the periodic table of chemical elements, cr, mo and W belong to the same main group, and all three metal elements can chemically react with red phosphorusFormation of CrP 2 ，MoP 2 And WP 2 . At present, the crystal structures of the three compounds reported in the literature are respectively: crP 2 Has a monoclinic structure (space group: C2/m) at the bottom center and an MoP 2 Having a bottom-centered orthogonal structure (space group: cmc 2) 1 ). And WP 2 Then two different crystal structures (bottom-centered orthogonal structure (space group: cmc 2) are obtained due to the difference in preparation temperature 1 ) And a bottom-centered monoclinic structure (space group: c2/m)). Cr, mo and W belong to the same main group and have very similar outer electronic structures. WP of 2 Has crystal polymorphism (i.e. the same chemical composition but different crystal structures). Then with WP 2 Isoelectronic compound MoP of the same main group 2 Is there also crystal polymorphism? The above CrP 2 ，MoP 2 And WP 2 The crystal is grown in a high-temperature furnace (a shaft furnace, a box furnace and the like) by using a fluxing agent method, and the pressure for synthesizing the sample is normal pressure. In a Mo-P binary phase diagram reported in the literature, the MoP of Mo and P is in the chemical ratio of 1 2 MoP with only orthorhombic structure at bottom center and monoclinic structure at bottom center 2 No report is made. The problem which cannot be overcome at present is that a high-temperature furnace which is common in a laboratory cannot provide a high-pressure (for example, 5GPa, about 5 ten thousand atmospheric pressures) environment for a sample reactant, and only the MoP can be prepared by a normal-pressure high-temperature preparation method 2 The basal-centric orthogonal phase of (a).
In addition, since the melting point of red phosphorus is low (590 degrees Celsius), and the melting points of Cr, mo and W are high, 1907 degrees Celsius, 2623 degrees Celsius and 3422 degrees Celsius, respectively. In the synthesis of the metal phosphorus-rich compound, the melting points of red phosphorus and metal elements have large temperature difference, so the temperature must be slowly increased under the premise of putting a large amount of fluxing agent (such as Sn) to prevent the quartz tube from tube explosion, and the sample preparation speed by the normal-pressure solid-phase method is slow (more than half a month). In addition, and most importantly, the vapor pressure of red phosphorus is very high (4357 kPa at 590 ℃, about 41 atmospheres), and when a metal phosphorus-rich compound is synthesized by a conventional method, there is a risk of tube explosion of a quartz tube at high temperature.
Disclosure of Invention
In view of the above-mentioned drawbacks of the prior art, the present invention aims to provide a monoclinic crystal and a preparation method thereof.
To achieve the above and other related objects, an aspect of the present invention provides a monoclinic crystal having a molecular formula of MoP 2 (ii) a The monoclinic crystal type substance comprises the following unit cell parameters
α＝90°，β＝119.192±0.006°，γ＝90°，
The crystal form space group is C2/m, and the crystal system belongs to a monoclinic system.
In some embodiments of the invention, in the monoclinic crystal form, mo is in an octadentate field, and each Mo atom is coordinated with 8P atoms.
In some embodiments of the invention, the monoclinic crystal type is a black crystal with metallic luster.
In another aspect, the present invention provides a method for preparing a monoclinic crystal form, the method comprising the steps of:
1) Tabletting elemental molybdenum and red phosphorus and then coating hexagonal boron nitride to prepare a coating body;
2) Reacting the inclusion in the step 1) at 900-1100 ℃ under the pressure of 4-6 GPa to obtain the monoclinic crystal system crystal form substance.
In some embodiments of the present invention, in step 1), the molar ratio of elemental molybdenum to red phosphorus is 1:2.5 to 3.5.
In some embodiments of the present invention, in the step 1), the single molybdenum and red phosphorus are ground and then pressed into a cylindrical shape.
In some embodiments of the invention, the cylinder has a diameter of 3.5 to 5.0 mm and a height of 3.2 to 6.0 mm.
In some embodiments of the invention, in step 1), the hexagonal boron nitride is selected from a hexagonal boron nitride sheet or a hexagonal boron nitride tube; the thickness of the hexagonal boron nitride sheet wrapping and pressing sheet is 0.5-0.8 mm; the thickness of the tube wall of the hexagonal boron nitride tube is 0.3-0.5 mm.
In some embodiments of the invention, in the step 2), after the reaction is finished, the temperature is reduced at a rate of 50 to 100 ℃ per hour, and the temperature of the sample is slowly reduced to 800 to 900 ℃; then quenching to room temperature, and finally slowly releasing pressure to normal pressure.
In some embodiments of the invention, step 2) is a reaction performed in a large cavity press.
In some embodiments of the present invention, the step 2) is performed by calibrating the pressure and temperature before the reaction; the pressure is calibrated by using a resistance-pressure curve of metal Bi; the temperature is calibrated by phase transition of the crystal structure of the silicon dioxide.
Drawings
FIG. 1 is a schematic view of an apparatus for synthesizing a sample at high temperature and high pressure according to the present invention.
FIG. 2 shows a MoP of the present invention 2 Single crystal samples and optical photographs of geometry.
FIG. 3 shows a MoP of the present invention 2 Single crystal sample orientation and high symmetry diffraction crystal face.
FIG. 4 shows a MoP of the present invention 2 Single crystal diffraction patterns of single crystal samples in three different directions ((a) (hk 0), (b) (h 0 l), (c) (0 kl)).
FIG. 5 shows a bottom-centered monoclinic system MoP of the present invention 2 A schematic diagram of a crystal structure.
FIG. 6 is a micro-area image of a sample of the present invention under an electron microscope.
FIG. 7 is a diagram showing the chemical element types and chemical compositions of the samples according to the present invention.
FIG. 8 shows a bottom-centered monoclinic system MoP of the present invention 2 Crystal and prior art orthorhombic phase MoP 2 The band structure of the crystal is simulated.
FIG. 9 shows a bottom-centered monoclinic system MoP of the present invention 2 Crystals and prior artOrthorhombic phase MoP for surgery 2 And (3) simulating the density of states of the crystal.
FIG. 10 shows a bottom-centered monoclinic system MoP of the present invention 2 Crystal and prior art orthorhombic phase MoP 2 Resistance test comparative plot of the crystal.
Detailed Description
The inventor of the invention finds that the difficulties in the prior art can be overcome by adopting a high-temperature high-pressure synthesis method through a large amount of experiments. The large-cavity press has the advantages of physical mechanical pressurization, magnesium oxide octahedral wrapping and pyrophyllite sealing, and can provide a sealed and high-strength sample cavity for a sample. The physical pressure provided by the large chamber 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 with high vapor pressure, plays an extremely important role in the research and exploration of new materials, and is an important means for preparing metal phosphorus-rich compounds. The MoP with the monoclinic structure is synthesized for the first time on a Kawai type large-cavity press of 2000 tons by adopting a high-temperature high-pressure method 2 A single crystal sample. On the basis of this, the present invention has been completed.
The first aspect of the present invention provides a monoclinic crystal substance, the structural formula of which is MoP 2 (ii) a The monoclinic crystal type substance comprises the following unit cell parameters
α＝90°，β＝119.192±0.006°，γ＝90°，
The crystal form space group is C2/m, and the crystal system belongs to a monoclinic system.
In the monoclinic crystal type provided by the invention, the measurement of single crystal data is not particularly limited, and a single crystal testing instrument known by a person skilled in the art can be adopted. In one embodiment, the monoclinic crystal is in Bruker (Bruker) for single crystal data) Single crystal X-ray diffraction data of monoclinic crystal type substances are collected at 150K on a D8 Venture double-target small molecule X-ray single crystal diffractometer, wherein Mo Ka radiation
Single crystal diffractometer tube pressure at data acquisition: 50kV and 30mA pipe flow. Analyzing the crystal structure by ShelXT 2018/2 (Sheldrick, 2018) to obtain all 3 non-hydrogen atom positions, correcting structure parameters and distinguishing atom types by using a least square method, obtaining all atom positions by using a geometric calculation method and a difference Fourier method, and finally obtaining a reliability factor R 1 ＝0.0557,wR 2 =0.1653, goodness factor (Goodness of fit on F) 2 ) =1.177. Finally determining the stoichiometric formula of the sample as MoP 2 The calculated molecular weight is 157.88, and the crystal density of the material is 5.726g/cm ～3 。
In the monoclinic crystal provided by the invention, mo is in an octadentate field in the monoclinic crystal, and each Mo atom is respectively coordinated with 8P atoms.
The crystal form substance further determines a molecular formula through energy dispersive spectroscopy analysis, wherein the molecular formula is MoP 2 . The invention adopts an energy dispersive spectroscopy (Desktop Scanning Electron Microscope-Phenom ProX) to analyze the chemical components of the sample.
In a second aspect, the present invention provides a method for preparing a monoclinic crystal according to the first aspect, comprising the steps of:
1) Tabletting elemental molybdenum and red phosphorus and then coating hexagonal boron nitride to prepare a coating body;
2) Reacting the inclusion in the step 1) at 900-1100 ℃ under the pressure of 4-6 GPa to obtain the monoclinic crystal system crystal form substance.
In the synthesis method of the monoclinic system crystal form substance, step 1) is to perform tabletting on single molybdenum and red phosphorus and then wrap hexagonal boron nitride to prepare the inclusion. Among them, the elemental molybdenum and red phosphorus need to be limited within a suitable ratio range. The molar ratio of the simple substance molybdenum to the red phosphorus is 1:2.5 to 3.5. In one embodiment, the molar ratio of elemental molybdenum to red phosphorus is 1:2.5 to 3; or 1:3 to 3.5. In general, elemental molybdenum and red phosphorus can be mixed in a glove box, for example, homogeneously in an argon atmosphere, mortar-milled for half an hour in an agate mortar, and pressed into a cylindrical shape having a diameter of 3.5 to 5.0 mm and a height of 3.2 to 6.0 mm by a powder tablet press (pressure: 5 mpa). In some embodiments, the diameter of the cylinder is 3.5 to 4.0 millimeters, 4.0 to 4.5 millimeters, or 4.5 to 5.0 millimeters, etc. The height of the cylinder is 3.2-4.0 mm, 4.0-5.0 mm, 5.0-6.0 mm, 3.5-5.5 mm, etc.
Hexagonal boron nitride belongs to a substance which is resistant to high temperature and high pressure and has stable chemical properties. In the invention, the hexagonal boron nitride can be a hexagonal boron nitride sheet or a hexagonal boron nitride tube. When hexagonal boron nitride tubes are used, the thickness of the tube wall may be, for example, 0.5 to 0.8 mm, 0.5 to 0.6 mm, 0.6 to 0.7 mm, or 0.7 to 0.8 mm, or 0.55 to 0.75 mm, 0.5 to 0.7 mm, 0.6 to 0.8 mm, or the like. The thickness of the hexagonal boron nitride tablet is 0.3-0.5 mm, 0.3-0.4 mm, or 0.4-0.5 mm. Because red phosphorus reacts with the noble metal Pt under high temperature and high pressure, the sample reactant is coated with hexagonal boron nitride which is resistant to high temperature and high pressure and stable in chemical property, so that the probability of generating impurity phases is reduced.
In the synthesis method of the monoclinic system crystal form substance, the monoclinic system crystal form substance is prepared by reacting the inclusion in the step 1) at 900-1100 ℃ and 4-6 GPa pressure in the step 2). In some embodiments, the reaction temperature may also be 900 to 1000 ℃, or 1000 to 1100 ℃,950 to 1050 ℃, or the like. The reaction pressure is 4-5 Gpa, or 5-6 Gpa, or 4.5-5.5 Gpa. In the step 2), after the reaction is finished, the temperature is reduced at the rate of 50-100 ℃ per hour, and the temperature of the sample is slowly reduced to 800-900 ℃; then quenching to room temperature, and finally slowly releasing pressure to normal pressure. In some embodiments, the temperature in the foregoing step may be decreased at a rate of 50 to 80 ℃, or 80 to 100 ℃,60 to 90 ℃, or 70 to 80 ℃ per hour. Slowly cooling the temperature of the sample to 800-850 ℃, or 850-900 ℃ and the like. Then quenching to room temperature, and finally slowly releasing pressure to normal pressure.
In general, any reactor capable of providing the above-mentioned high temperature and high pressure may be used. In some embodiments, for example, a large cavity press may be used for the reaction, more specifically, a Kawai type large cavity press, and further, a Kawai type large cavity press of 2000 tons may be selected. When the method is used, as shown in fig. 1, the inclusion is placed into a tantalum heating furnace, the periphery of the inclusion can be sealed by zirconium dioxide heat insulation plugs, a carbon heating furnace is placed into a silicon dioxide heat insulation pipe, finally, the carbon heating furnace is placed into a pressure transfer medium in magnesium oxide octahedron doped with 5% cobalt oxide, and sample synthesis is carried out on a 2000-ton Kawai type large-cavity press. And after the high-pressure and high-temperature conditions, the temperature reduction and the pressure relief are controlled, a sample is taken out from the magnesium oxide octahedron, and black crystals with metallic luster are observed under a microscope.
It is further noted that, in the step 2), before the reaction, calibration of pressure and temperature is performed; the pressure is calibrated by using a resistance-pressure curve of the metal Bi; the temperature is calibrated by phase transition through the crystal structure of the silicon dioxide. And the heating temperature is controlled by a method for controlling the heating power, and the temperature is measured by a tungsten-rhenium thermocouple.
The invention has the following beneficial effects:
the method can overcome the limit that the red phosphorus vapor pressure is high and the quartz tube is easy to explode, thereby preparing the MoP with the monoclinic structure at the bottom core 2 The single crystal has good crystallization quality, is single-phase through single crystal X-ray diffraction, and has no impurity and goldenrain crystal in the single crystal.
Orthorhombic and monoclinic phase MoP 2 All belong to compensation type semimetal materials, and are expected to be applied to the fields of magnetic memories, magnetic sensors or magnetic switches and the like. Orthogonal phase MoP 2 Is a three-dimensional stacked crystal structure (MoP) 7 The polyhedron is linked along the a-axis (composed of three phosphorus atoms), the b-axis is linked by points (phosphorus atoms), and the c-axis is a complex link (point link and edge link)), so that the chemical bond is strong. Want to reduce the sampleThin, difficult and not easy to be made into devices. The monoclinic phase belongs to a layered material, and Van der Waals bonds are bonded between layers, so that the chemical bonds are weak, and the monoclinic phase is easy to be made into a film. In addition, it is also the most important point that, from the thermodynamic viewpoint, the orthorhombic phase belongs to the low-temperature phase, and the monoclinic phase belongs to the high-temperature phase. When the above materials are applied to a device, heat is generated during use. Therefore, the high-temperature monoclinic phase is more stable in performance than the low-temperature orthorhombic phase.
The following examples are provided to further illustrate the advantageous effects of the present invention.
In order to make the objects, technical solutions and advantageous technical effects of the present invention more clear, the present invention is further described in detail below with reference to examples. However, it should be understood that the embodiments of the present invention are only for explaining the present invention and are not for limiting the present invention, and the embodiments of the present invention are not limited to the embodiments given in the specification. The examples were made under conventional conditions, or conditions recommended by the material suppliers, without specifying specific experimental conditions or operating conditions.
Furthermore, it is to be understood that one or more method steps mentioned in the present invention does not exclude that other method steps may also be present before or after the combined steps or that other method steps may also be inserted between these explicitly mentioned steps, unless otherwise indicated; it is also to be understood that a combined connection between one or more devices/apparatus as referred to in the present application does not exclude that further devices/apparatus may be present before or after the combined device/apparatus or that further devices/apparatus may be interposed between two devices/apparatus explicitly referred to, unless otherwise indicated. Moreover, unless otherwise indicated, the numbering of the various method steps is merely a convenient tool for identifying the various method steps, and is not intended to limit the order in which the method steps are arranged or the scope of the invention in which the invention may be practiced, and changes or modifications in the relative relationship may be made without substantially changing the technical content.
In the following examples, reagents, materials and instruments used are commercially available unless otherwise specified.
Example 1
1) Preparation of cylindrical reactant of molybdenum and red phosphorus under normal pressure
Chemically pure elemental molybdenum and red phosphorus were mixed homogeneously in a glove box at a molar ratio of 1.5, in a mortar for half an hour in an agate mortar. The reaction powder was pressed into a cylinder having a diameter of 3.5 mm and a height of 3.2 mm by a powder tablet press (pressure: 5 MPa). Because red phosphorus reacts with the noble metal Pt under high temperature and high pressure, the sample reactant is wrapped by hexagonal boron nitride which is resistant to high temperature and high pressure and stable in chemical property, so that the probability of generating impurity phases is reduced, and the sample reactant is different from the sample wrapped by the noble metal in the existing high-temperature and high-pressure experiment.
2) And putting the sample and the hexagonal boron nitride protective sleeve into a tantalum heating furnace. The samples were then loaded into a high pressure assembly for high pressure high temperature synthesis (see FIG. 1 for assembly drawings). Sample synthesis was performed on a 2000 ton Kawai type large cavity press. Slowly increasing the pressure to 5GPa at room temperature, starting a heating program to heat to 1100 ℃, preserving the heat for 2 hours under the condition of high temperature and high pressure, then reducing the temperature at the rate of 100 ℃ per hour, slowly reducing the temperature of the sample to 900 ℃, then quenching to room temperature, and finally slowly releasing the pressure to normal pressure. The sample was taken out of the octahedron of magnesium oxide and was seen under a microscope as a black crystal with metallic luster (see fig. 2).
Single crystal X-ray diffraction analysis of samples obtained after quenching, FIG. 3 is a MoP of the invention 2 The single crystal sample has crystal orientation and high symmetry diffraction crystal face. From FIG. 4, it can be seen that the single crystal diffraction spots of the samples are small and bright, confirming that the MoP prepared by the present invention is 2 The single crystal has no impurity and goldenrain phenomenon, and has good crystallization quality. A crystallography Information File (crystallography Information File) of the sample is obtained by single crystal analysis software, and the lattice parameters are as follows: space group: c2/m, unit cell parameters are:
β =119.192 degrees. Based on the resolved crystallographic information file, the inventors drawn a bottom-centered monoclinic system MoP 2 Crystal of (2)Schematic structure (fig. 5), 8P atoms are around each Mo atom.
Example 2
1) Preparation of cylindrical reactant of molybdenum and red phosphorus under normal pressure
Chemically pure elemental molybdenum and red phosphorus were mixed homogeneously in a molar ratio of 1. The molybdenum-phosphorus powder was pressed into a cylinder having a diameter of 3.5 mm and a height of 3.2 mm by a powder tablet press. The initial reactant of the cylindrical sample is protected by a hexagonal boron nitride tube and a wafer, so that the probability of generating impurity phases is reduced.
2) And putting the sample and the hexagonal boron nitride protective sleeve into a tantalum heating furnace. The samples were then loaded into a high pressure assembly for high pressure high temperature synthesis on a 2000 ton Kawai type large cavity press. Slowly increasing the pressure to 6GPa at room temperature, starting a heating program to heat to 1200 ℃, preserving the heat for 3 hours under the condition of high temperature and high pressure, then reducing the temperature at the rate of 100 ℃ per hour, slowly reducing the temperature of the sample to 1000 ℃, then quenching to room temperature, and finally slowly releasing the pressure to normal pressure. The excess phosphorus is used as a self-fluxing agent, and after taking out a sample, the fluxing agent is removed by dilute nitric acid.
In the same manner as in example 1, the sample obtained after quenching also had a metallic lustrous single crystal, and it was found that the sample had a monoclinic system and had good crystal quality without the presence of goldenrain crystals and impurities by conducting single crystal X-ray diffraction studies.
Example 3
1) Preparation of cylindrical reactant of molybdenum and red phosphorus under normal pressure
Chemically pure elemental molybdenum and red phosphorus were mixed homogeneously in a glove box at a molar ratio of 1.5, and ground in an agate mortar for half an hour. The molybdenum-phosphorus powder was pressed into a cylinder having a diameter of 3.5 mm and a height of 3.2 mm by a powder tablet press. The initial reaction of the cylindrical sample is protected by a hexagonal boron nitride tube and a wafer, so that the probability of generating impurity phases is reduced.
2) And putting the sample and the hexagonal boron nitride protective sleeve into a tantalum heating furnace. The samples were then loaded into a high pressure assembly for high pressure high temperature synthesis on a 2000 ton Kawai type large cavity press. Slowly increasing the pressure to 4GPa at room temperature, starting a heating program to heat to 1000 ℃, preserving the heat for 3 hours under the condition of high temperature and high pressure, then reducing the temperature at the rate of 100 ℃ per hour, slowly reducing the temperature of the sample to 900 ℃, then quenching to room temperature, and finally slowly releasing the pressure to normal pressure.
In the same manner as in example 1, the sample obtained after quenching also had a metallic luster single crystal, and it was found that the sample had a monoclinic system and had good crystal quality without the presence of goldenrain crystals and impurities by conducting a single crystal X-ray diffraction study.
The crystal obtained in example 1 was subjected to single crystal X-ray diffraction measurement as follows:
MoP was collected at 150K on a Bruker (Bruker) D8 Venture double target small molecule X-ray single crystal diffractometer 2 Single crystal X-ray diffraction data of (1), in which a molybdenum target is irradiated
Single crystal diffractometer tube pressure at data acquisition: 50kV and 30mA pipe flow. Analyzing the crystal structure by ShelXT 2018/2 (Sheldrick, 2018) to obtain all 3 non-hydrogen atom positions, correcting structure parameters and distinguishing atom types by using a least square method, obtaining all atom positions by using a geometric calculation method and a difference Fourier method, and finally obtaining a reliability factor R 1 ＝0.0557,wR 2 =0.1653, goodness factor (Goodness of-fit on F) 2 ) =1.177. The final structural optimization is done using the SHELL program, using full matrix techniques to minimize F 2 The square sum deviation of. The results are detailed in table 1.
TABLE 1.MoP 2 Crystal data and structure refinement (150K)
The crystals obtained in example 1 were subjected to energy dispersive x-ray spectroscopy as follows:
the invention passes energy dispersion X-ray energy spectrum (test condition: region size: 112 micrometers, voltage, 15KV, point detector (BSD)Full)) the chemical composition of the sample was analyzed. FIG. 6 is a micro-area image of a sample under an electron microscope (FOV: 112 μm, mode:15kV-Point, detector: BSD Full, time: OCT 27 2020 15. Fig. 7 shows the chemical element species and chemical composition analysis of the samples. The experimental result shows that the sample only contains two elements of molybdenum and phosphorus. As shown in table 2, the ratio of molybdenum is 33.51%, the ratio of phosphorus is 66.49%, the chemical ratio of molybdenum to phosphorus is 1 2 。
TABLE 2 analysis of the chemical elements contained in the samples
Example 4
Monoclinic phase MoP of the invention 2 And prior art orthorhombic phase MoP 2 Simulation of band structure and density of states
Simulation software name: cambridge Serial Total Energy Package (CAStep)
1) Simulation parameters: exchange association can: generalized Gradient Approximation (GGA);
2) Energy cutting: 290 electron volts (monoclinic phase);
3) Size of the inverse space grid: 8 by 4;
4) Energy error: 1*10 -6 Electron volts per atom.
The test results are shown in fig. 8 and 9.
Orthogonal phase MoP 2 And monoclinic phase MoP 2 Are all of compensated semi-metallic material, as shown in FIG. 8, quadrature phase MoP 2 And monoclinic phase MoP 2 The valence band top and the conduction band bottom of (1) do not overlap near the fermi surface, and are expected to be applied to the fields of magnetic memories, magnetic sensors or magnetic switches and the like. Orthogonal phase MoP 2 Is a three-dimensional stacked crystal structure (MoP) 7 The polyhedron is linked along the a-axis by a face (composed of three phosphorus atoms), the b-axis by a point (phosphorus atom), the c-axis by a complex linkage (point linkage and edge linkage)), and a chemical bondIt is stronger. Therefore, it is difficult to thin the sample and to fabricate the device. And monoclinic phase MoP 2 The composite material belongs to a layered material, and Van der Waals bonds are bonded between layers, so that the chemical bonds are weak, and the composite material is easy to be made into a film. FIG. 8 shows the band structure of the orthorhombic phase (black dotted line) and monoclinic phase (red solid line) MoP2, and it can be seen from FIG. 8 that although the orthorhombic phase MoP 2 The crystal symmetry (space group No. 36) is higher than that of the monoclinic phase (space group No. 12), but by contrast, the orthorhombic phase MoP 2 With monoclinic phase MoP 2 The applicant finds that the band structure of the orthogonal phase is more complex than that of the monoclinic phase, the electronic structure of a sample is difficult to analyze, and the future device planning design is not facilitated. FIG. 9 shows the results of comparing the state densities of the orthorhombic phase (black dotted line) and the monoclinic phase (red solid line), and the monoclinic phase MoP is present near the Fermi surface 2 The density of states of (a) is 2 electron/electron volts, and the density of states of the orthogonal phase is 1 electron/electron volt. The above results show that the monoclinic phase MoP 2 And the method has more advantages in future device development than the orthogonal phase.
Example 5
Monoclinic phase MoP of the invention 2 And the existing orthorhombic phase MoP 2 Resistance test experiment of
The instrumentation used was tested: physical Property Measurement System (PPMS)
The test method comprises the following steps: the four-electrode method is calibrated, namely two electrodes are electrified, and the other two electrodes are tested for voltage.
A link wire: gold wire, attached to the sample with conductive silver paste.
Temperature range: 2-300 opener
The current magnitude is as follows: 50 milliamp
And (3) testing results: FIG. 10, orthogonal phase MoP 2 With monoclinic phase MoP 2 The resistance value is between 0.09 ohm and 0.18 ohm which is equivalent to the resistance value of common metal. Orthogonal phase MoP 2 Resistance value ratio of (1) to monoclinic phase MoP 2 The temperature is higher in the whole temperature test range, and the experimental result is consistent with the theoretical simulation result of the invention.The monoclinic phase resistance value is low, and when the monoclinic phase resistance value is made into a device in the future, the power consumption is low, the heat effect is low, and the safety operation of the device is facilitated.
MoP of the invention 2 The monoclinic system belongs to a compensation type semimetal material and is expected to be applied to the fields of magnetic memories, magnetic sensors, magnetic switches and the like.
The above embodiments are merely illustrative of the principles and utilities of the present application and are not intended to limit the present application. Any person skilled in the art can modify or change the above-described embodiments without departing from the spirit and scope of the present application. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical concepts disclosed in the present application shall be covered by the claims of the present application.
Claims (9)
1. A monoclinic crystal substance, the molecular formula of which is MoP 2 ；
The monoclinic crystal type substance comprises the following unit cell parameters
α＝90°，β＝119.192±0.006°，γ＝90°，
The crystal form space group is C2/m, and the crystal system belongs to a monoclinic system.
2. The monoclinic crystal of claim 1, wherein Mo is in an octadentate field and each Mo atom is coordinated with 8P atoms;
and/or the monoclinic crystal type substance is a black crystal with metallic luster.
3. A method of preparing a monoclinic crystal according to any one of claims 1 to 2, comprising the steps of:
1) Tabletting elementary molybdenum and red phosphorus and then coating hexagonal boron nitride to prepare a coating body; the molar ratio of the simple substance molybdenum to the red phosphorus is 1:2.5 to 3.5;
2) Reacting the inclusion in the step 1) at 900-1100 ℃ under the pressure of 4-6 GPa to obtain the monoclinic crystal type substance.
4. The method according to claim 3, wherein in the step 1), the single molybdenum and red phosphorus are ground and then pressed into a cylindrical shape.
5. The method of claim 4, wherein the diameter of the cylinder is 3.5-5.0 mm and the height is 3.2-6.0 mm.
6. The method according to claim 3, wherein in step 1), the hexagonal boron nitride is selected from hexagonal boron nitride flakes or hexagonal boron nitride tubes; the thickness of the hexagonal boron nitride sheet wrapping tablet is 0.5-0.8 mm; the thickness of the tube wall of the hexagonal boron nitride tube is 0.3-0.5 mm.
7. The method for preparing a monoclinic crystal form according to claim 3, wherein in the step 2), after the reaction is finished, the temperature is reduced at a rate of 50-100 ℃ per hour, and the temperature of the sample is slowly reduced to 800-900 ℃; then quenching to room temperature, and finally slowly releasing pressure to normal pressure.
8. The method according to claim 3, wherein the step 2) is carried out in a large chamber press.
9. The method according to claim 3, wherein the step 2) comprises calibrating the pressure and temperature before the reaction; the pressure is calibrated by using a resistance-pressure curve of metal Bi; the temperature is calibrated by phase transition of the crystal structure of the silicon dioxide.
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| US20020062858A1 (en) * | 1992-09-21 | 2002-05-30 | Thomas Mowles | High efficiency solar photovoltaic cells produced with inexpensive materials by processes suitable for large volume production |
| US20200043978A1 (en) * | 2018-07-31 | 2020-02-06 | International Business Machines Corporation | Magnetic field controlled transistor |
| CN111495399A (en) * | 2020-05-08 | 2020-08-07 | 桂林理工大学 | S-doped WP2Nanosheet array electrocatalyst and preparation method thereof |
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| US20020062858A1 (en) * | 1992-09-21 | 2002-05-30 | Thomas Mowles | High efficiency solar photovoltaic cells produced with inexpensive materials by processes suitable for large volume production |
| US20200043978A1 (en) * | 2018-07-31 | 2020-02-06 | International Business Machines Corporation | Magnetic field controlled transistor |
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