阅读说明：本技术 基于金刚石对顶砧的综合原位电输运测量方法 (Comprehensive in-situ electric transport measurement method based on diamond anvil cell ) 是由 岳冬辉 秦天茹 高春晓 韩永昊 于 2020-10-10 设计创作，主要内容包括：本发明的基于金刚石对顶砧的综合原位电输运测量方法属于高压原位电磁学测量的技术领域,具体步骤为：首先利用物理气相沉积结合光刻技术在两颗压砧表面制备复合电极；然后制作复合绝缘垫片并复位,在样品腔内放置样品并放置红宝石,利用红宝石荧光峰标定实验压力,将圆形平行板电极的两根引线与阻抗谱仪器相连接,施加交流电压进行交流频率响应测量；将四电极的四根引线与霍尔系统连接,进行直流电输运参数测量。本发明采用全新的电极构型,将四电极和平行板电极集成于一体,为高压环境下系列电磁参数的协同测量提供了可能,有效避免了由于独立测量过程中实验环境的差异,造成彼此数据关联性的丧失。(The invention discloses a comprehensive in-situ electric transport measurement method based on a diamond anvil cell, belonging to the technical field of high-voltage in-situ electromagnetic measurement, and comprising the following specific steps: firstly, preparing a composite electrode on the surfaces of two anvils by combining physical vapor deposition with a photoetching technology; then, manufacturing a composite insulating gasket and resetting, placing a sample and ruby in the sample cavity, calibrating the experimental pressure by using the ruby fluorescence peak, connecting two leads of the circular parallel plate electrode with an impedance spectrometer, and applying alternating voltage to perform alternating frequency response measurement; four leads of the four electrodes are connected with a Hall system to measure direct current transport parameters. The invention adopts a brand-new electrode configuration, integrates the four electrodes and the parallel plate electrodes into a whole, provides possibility for cooperative measurement of series electromagnetic parameters in a high-voltage environment, and effectively avoids loss of data correlation caused by difference of experimental environments in an independent measurement process.)

1. A comprehensive in-situ electric transport measurement method based on diamond anvil cells comprises the steps of firstly, preparing composite electrodes on the surfaces of two anvil cells by utilizing physical vapor deposition and photoetching technology, manufacturing circular parallel plate electrodes with the same diameter on the surfaces of the upper anvil cell and the lower anvil cell for measuring alternating current frequency response of a sample, uniformly etching four windows on the periphery of the circular electrode on one side at equal intervals, manufacturing four electrodes in the four windows, and connecting copper wires with the side electrodes of the anvil cells for circuit lead wires to obtain four electrodes for measuring direct current electric transport parameters; then, manufacturing a composite insulating gasket and resetting, placing a sample and ruby in the sample cavity, extruding the composite insulating gasket through two anvils, generating high voltage for the sample placed in the composite insulating gasket, calibrating experiment pressure by using a ruby fluorescence peak, connecting two leads of a circular parallel plate electrode with an impedance spectrometer, applying alternating voltage, and carrying out alternating frequency response measurement; four leads of the four electrodes are connected with a Hall system to measure direct current transport parameters.

2. The diamond anvil cell-based comprehensive in-situ electric transport measurement method according to claim 1, wherein the specific process for preparing the composite electrode is as follows:

firstly, respectively depositing a layer of metal molybdenum on the contact surface of a cleaned diamond anvil cell by using a magnetron sputtering device as an electrode material, wherein the parameters of the magnetron sputtering device are as follows: the working gas is Ar, the pressure of a vacuum cavity is 0.8-1.2 Pa, the substrate temperature is 200-300 ℃, and the thickness of a prepared molybdenum layer is 2-4 mu m;

secondly, uniformly coating a layer of photoresist on the surface of the anvil cell plated with the molybdenum film, respectively exposing the electrode configurations on the surfaces of two anvil cells by using a photoetching device, wherein one of the two anvil cells is a simple circular electrode, the other anvil cell integrates four electrodes with the circular electrode, etching the exposed part by using NaOH developing solution, and then removing the redundant molybdenum layer by using mixed solution of nitric acid, phosphoric acid, acetic acid and water of 9:4:14:7 as corrosive solution to prepare electrodes on the surface of the diamond anvil cell;

thirdly, respectively depositing an aluminum oxide protective layer on the surface of the anvil of the prepared electrode by using the magnetron sputtering device again, wherein the parameters of the magnetron sputtering device are as follows: the target material is metallic aluminum, and the working gas is O with the flow ratio of 30:2.4₂And Ar, wherein the pressure of a vacuum cavity is 0.8-1.2 Pa, the substrate temperature is 200-300 ℃, and the thickness of the prepared alumina layer is 2-4 mu m;

and fourthly, removing the aluminum oxide film on the surface of the circular electrode and at the bottom of the lateral edge of the anvil through photoetching and chemical corrosion to ensure that the circular parallel plate electrode and the four electrodes can be contacted with a sample in the sample cavity, connecting the copper wire with the exposed metal molybdenum layer at the bottom of the anvil through silver paste, and curing for 2 hours at 150 ℃.

3. The method for comprehensively measuring in-situ electric transportation based on the diamond anvil cell according to claim 1, wherein the composite insulating gasket is manufactured and reset by the following specific processes:

firstly, prepressing a T301 steel gasket with the thickness of 200-250 microns by using an anvil after leveling centering, wherein the thickness of an indentation after prepressing is 30-90 microns;

secondly, punching the pre-pressed gasket by using a laser cutting device, wherein the round hole and the indentation of the anvil surface are in concentric circles, and the aperture size is smaller than the size of the anvil surface;

thirdly, resetting the punched gasket, embedding the reduction anvil into the indentation of the gasket, filling insulating powder into the indentations on the upper side and the lower side of the gasket and the punched round hole in sequence, and extruding the insulating powder by using the anvil to ensure that insulating layers are uniformly distributed between the contact surfaces of the two anvils and the gasket, wherein the thickness of the insulating layers is 10-15 microns;

fourthly, punching the prepared gasket by using a laser cutting device to obtain a sample cavity, and ensuring that the circular hole and the indentation are concentric, wherein the aperture size of the sample cavity is smaller than that of the gasket punched in the second step;

4. the method for comprehensively measuring in-situ electric transportation based on the diamond anvil cell according to claim 1, wherein the insulating powder is obtained by mixing alumina powder or cubic boron nitride powder with epoxy resin according to a mass ratio of 4: 1.

5. The method of claim 1, wherein the window is a square tangential to the circular parallel plate electrode, and the ratio of the side length of the square to the diameter of the circular parallel plate electrode is less than 1: 10.

The technical field is as follows:

the invention belongs to the technical field of high-voltage in-situ electromagnetic measurement, and particularly relates to a cooperative measurement method for various in-situ electric transport properties (resistance, magnetic resistance, carrier concentration, mobility, Hall coefficient, dielectric constant and the like) based on a diamond anvil cell.

Technical background:

extreme temperature and pressure are used as effective technical means for regulating and controlling the structure and physical properties of the material, and the method is widely applied to the fields of research and development of new materials, analysis of phases, exploration of earth science and planet science and the like. The Diamond Anvil Cell (DAC for short) is the only static high-pressure generating device capable of realizing a million atmosphere environment, is an important support for extreme temperature and pressure science, can realize static maximum temperature and pressure, and is compatible with various characterization instruments, such as: the high-pressure in-situ measurement of physical properties such as optics, thermodynamics, electromagnetism is realized by an X-ray diffraction device, a laser Raman device, a high-resolution microscope, infrared/ultraviolet and the like. In recent years, many temperature-pressure induced singular physical properties have been discovered based on the various in situ measurement methods described above for DAC.

Electromagnetism is an important branch of electromagnetism, and can be used for exploring phenomena such as material electronic structure phase change, metallization phase change, pressure-induced superconduction and the like under an extreme temperature and pressure environment, which is important for the cognition of material physical properties. For example: by systematically analyzing the structural phase change and the electric transport change of the semiconductor material in the high-pressure environment, the characteristics and the rules of the structural phase change, the structural phase change with equal structure, the electronic topological phase change and the like of the semiconductor under the action of pressure can be explored, the relevance of the electric transport parameters and the carrier behaviors to the phase changes of various levels of structures can be further obtained, the condensed state theory is enriched, and a new rule and a new phenomenon can be finally discovered. Through iterative updating of a DAC technical method, the common electromagnetic parameters can be basically measured under a high-voltage environment. Measurements of high-voltage electromagnetism can be roughly divided into two categories according to different characterization instruments: by using an alternating current frequency response (electrochemical impedance spectroscopy) analysis device, the determination of material relaxation frequency, relaxation time, dielectric constant and dielectric loss and the separation of crystal grains and grain boundary resistance can be realized in the DAC; by utilizing an electric transport property (Hall effect) measuring system, the measurement of experimental parameters such as carrier concentration, mobility, resistivity, magnetic resistance, Hall coefficient and the like can be realized in the DAC.

However, the geometric configurations of the electrodes required by the two types of high-voltage in-situ electromagnetic measurement are different, wherein the alternating-current frequency response analysis generally adopts a parallel-plate-like electrode, and the disc-shaped electrodes on the upper side and the lower side of the sample and the sample are completely covered, so that unnecessary edge effects are eliminated; the Hall effect measurement generally adopts four electrodes, and the electrodes are arranged on one side of a sample and are in point contact with the sample as much as possible so as to meet the measurement principle of the Van der Pauer method. Different electrode configurations present challenges for the cooperative measurement of a series of electrical parameters, severely limiting the contribution and mechanism of the multi-angle cognitive electrotransport process to the material structure, the change law of physical properties, and the bulk properties. For example, in high-voltage research on thermoelectric properties of materials, the electrical conductivity, the thermal conductivity and the thermoelectromotive force of a sample need to be determined, wherein the electrical conductivity and the thermoelectromotive force need electrodes with different configurations for measurement, and due to differences of experimental environments, the independent measurement of the parameters inevitably causes the loss of the correlation between the parameters and is not beneficial to decoupling the intrinsic mechanism of thermoelectric parameter change of the materials. Therefore, the innovation of the technical method is urgently needed, and the coordinated measurement of the series of electric transport parameters is realized based on the DAC.

The invention content is as follows:

the invention aims to solve the technical problem of realizing the cooperative measurement of series electric transport parameters such as material in-situ resistivity, magnetic resistance, carrier concentration, mobility, relaxation time, dielectric constant, Hall coefficient and the like under high pressure by designing the electrode configuration on the diamond anvil cell.

The technical scheme of the invention is as follows.

A comprehensive in-situ electric transport measurement method based on diamond anvil cells comprises the steps of firstly, preparing composite electrodes on the surfaces of two anvil cells by utilizing physical vapor deposition and photoetching technology, manufacturing circular parallel plate electrodes with the same diameter on the surfaces of the upper anvil cell and the lower anvil cell for measuring alternating current frequency response of a sample, uniformly etching four windows on the periphery of the circular electrode on one side at equal intervals, manufacturing four electrodes in the four windows, and connecting copper wires with the side electrodes of the anvil cells for circuit lead wires to obtain four electrodes for measuring direct current electric transport parameters; then, manufacturing a composite insulating gasket and resetting, placing a sample and ruby in the sample cavity, extruding the composite insulating gasket by two anvils, generating high voltage on the sample placed in the composite insulating gasket, calibrating the experimental pressure by using the ruby fluorescence peak, connecting two leads of the circular parallel plate electrode with an impedance spectrometer, applying alternating voltage, and carrying out alternating frequency response measurement; four leads of the four electrodes are connected with a Hall system to measure direct current transport parameters.

The specific process for preparing the composite electrode is as follows:

firstly, respectively depositing a layer of metal molybdenum on the contact surface of a cleaned diamond anvil cell by using a magnetron sputtering device as an electrode material, wherein the parameters of the magnetron sputtering device are as follows: the working gas is Ar, the pressure of a vacuum cavity is 0.8-1.2 Pa, the substrate temperature is 200-300 ℃, and the thickness of a prepared molybdenum layer is 2-4 mu m;

secondly, uniformly coating a layer of photoresist on the surface of the anvil cell plated with the molybdenum film, respectively exposing the electrode configurations on the surfaces of two anvil cells by using a photoetching device, wherein one of the two anvil cells is a simple circular electrode, the other anvil cell integrates four electrodes with the circular electrode, etching the exposed part by using NaOH developing solution, and then removing the redundant molybdenum layer by using mixed solution of nitric acid, phosphoric acid, acetic acid and water of 9:4:14:7 as corrosive solution to prepare electrodes on the surface of the diamond anvil cell;

thirdly, respectively depositing an aluminum oxide protective layer on the surface of the anvil of the prepared electrode by using the magnetron sputtering device again, wherein the parameters of the magnetron sputtering device are as follows: the target material is metallic aluminum, and the working gas is O with the flow ratio of 30:2.4₂And Ar, wherein the pressure of a vacuum cavity is 0.8-1.2 Pa, the substrate temperature is 200-300 ℃, and the thickness of the prepared alumina layer is 2-4 mu m;

and fourthly, removing the aluminum oxide film on the surface of the circular electrode and at the bottom of the lateral edge of the anvil through photoetching and chemical corrosion to ensure that the circular parallel plate electrode and the four electrodes can be contacted with a sample in the sample cavity, connecting the copper wire with the exposed metal molybdenum layer at the bottom of the anvil through silver paste, and curing for 2 hours at 150 ℃.

The composite insulating gasket is manufactured and reset, and the specific process is as follows:

firstly, prepressing a T301 steel gasket with the thickness of 200-250 microns by using an anvil after leveling centering, wherein the thickness of an indentation after prepressing is 30-90 microns;

secondly, punching the pre-pressed gasket by using a laser cutting device, wherein the round hole and the indentation of the anvil surface are in concentric circles, and the aperture size is smaller than the size of the anvil surface; for example: the diameter of the anvil surface is 300 μm, and the diameter of the circular hole can be 150-200 μm.

Thirdly, resetting the punched gasket, embedding the reduction anvil into the indentation of the gasket, filling insulating powder into the indentations on the upper side and the lower side of the gasket and the punched round hole in sequence, and extruding the insulating powder by using the anvil to ensure that insulating layers are uniformly distributed between the contact surfaces of the two anvils and the gasket, wherein the thickness of the insulating layers is 10-15 microns;

fourthly, punching the prepared gasket by using a laser cutting device to obtain a sample cavity, and ensuring that the circular hole and the indentation are concentric, wherein the aperture size of the sample cavity is smaller than that of the gasket punched in the second step; for example: if the pore size in step two is 150 μm, the pore size may be 100 μm.

The insulating powder is obtained by mixing alumina powder or cubic boron nitride powder and epoxy resin according to the mass ratio of 4: 1.

The window is a square tangent to the circular parallel plate electrode, and preferably, the ratio of the side length of the square to the diameter of the circular parallel plate electrode is less than 1: 10.

The invention is a result obtained under the subsidization of the national key research and development project (2018YFA0702703) and the national natural science fund project (11674404, 11774126). The main work is done in the key laboratory of the super-hard material country of Jilin university. The invention abandons the manual wiring of the traditional electrode, adopts the deposition and photoetching technology to prepare the film electrode on the surface of the diamond anvil cell, and ensures the accurate experimental size and geometric position. Meanwhile, a brand new electrode configuration is adopted, the four electrodes and the parallel plate electrodes are integrated into a whole, the design provides possibility for cooperative measurement of series electromagnetic parameters in a high-voltage environment, and loss of data correlation caused by difference of experimental environments in an independent measurement process is effectively avoided.

Description of the drawings:

FIG. 1 is a flow chart of the process for preparing the insulating gasket of the present invention.

FIG. 2 is a flow chart of a composite electrode fabrication process of the present invention.

FIG. 3 is a cross-sectional view of the composite electrode assembly of the present invention.

FIG. 4 is a schematic three-dimensional assembly of the composite electrode of the present invention.

FIG. 5 is a diagram of an experimental model of a composite electrode using finite element analysis.

FIG. 6 is a graph of experimental error in analyzing the size of different electrodes using finite elements.

FIG. 7 shows CaMoO in example 5₄Impedance spectrum of the sample under different pressures.

FIG. 8 is CaMoO in example 5₄The resistance, relaxation frequency and relative dielectric constant of the sample are related to the change of pressure.

FIG. 9 is MoO in example 6₂The resistivity of the sample is plotted against the pressure.

FIG. 10 is MoO in example 6₂The carrier concentration and the mobility of the sample are in a relation graph with the change of pressure.

The specific implementation mode is as follows:

example 1: the process for preparing the insulating pad will be described with reference to FIG. 1

Firstly, cleaning diamond anvils (the anvil surfaces of the anvils in the case of the example are 300 microns in diameter), fixing the two anvils in a press, and carrying out leveling and centering treatment to ensure that the anvil surfaces of the two anvils are in concentric circles and are parallel.

And secondly, selecting a T301 steel sheet with the initial thickness of 200-300 microns as a gasket material, and performing pre-pressing treatment by using an adjusted anvil to press the gasket to 30-90 microns.

And thirdly, drilling holes at the anvil surface indentation of the gasket by using a laser cutting device, wherein the round holes and the anvil surface indentation are in concentric circles, and the aperture is smaller than the diameter of the anvil surface (150-200 microns can be selected).

And fourthly, filling the ground insulating powder (alumina powder and epoxy resin in a ratio of 4:1) into the hole diameter and uniformly covering the inner wall of the indentation of the gasket, and extruding the insulating powder by using an anvil to ensure that the anvil and the gasket are isolated by an insulating powder layer 6 (the thickness of the insulating powder layer is 5-15 microns).

And fifthly, drilling the prepared gasket (containing the insulating layer) by using the laser cutting device again, wherein a round hole (serving as a sample cavity) and the anvil surface indentation also keep concentric circles, and the diameter of the sample cavity is smaller than that of the sample cavity in the third step (the diameter of the sample cavity can be selected to be 100 microns).

Example 2: the preparation process of the composite electrode will be described with reference to FIG. 2

Firstly, respectively depositing a layer of metal molybdenum film on the surfaces of two diamond anvils by using a magnetron sputtering device, wherein the specific experimental parameters are as follows: working gas: ar, vacuum chamber pressure: 0.8-1.2 Pa, substrate temperature: 200-300 ℃, thickness of molybdenum layer: 2 to 4 μm.

And secondly, uniformly and rotationally coating photoresist (positive photoresist) on the surface of the molybdenum film through a spin coater, respectively etching electrode shapes on two anvils by utilizing a photoetching technology (the surface of one anvil is a circular electrode, the surface of the other anvil is a circular + four probe electrodes, as shown in figure 2), exposing the redundant part, and removing the photoresist of the exposed part by using NaOH developing solution. The exposed molybdenum layer was then etched away using an etchant (a mixed solution of nitric acid, phosphoric acid, acetic acid, and water at 9:4:14: 7), and the unexposed photoresist was washed with acetone.

Thirdly, depositing a layer of aluminum oxide protection on the surfaces of the two anvils by using the magnetron sputtering device again, wherein the specific experimental parameters are as follows: target material: metallic aluminum target, working gas: o at a flow ratio of 30:2.4₂And Ar, vacuum chamber pressure: 0.8-1.2 Pa, substrate temperature: preparing the thickness of an aluminum oxide layer at 200-300 ℃:2 to 4 μm.

And fourthly, modifying the configuration of the alumina protective layer by means of photoetching and chemical etching, removing the contact part of the anvil and the sample and the photoresist at the bottom of the lateral edge of the anvil by means of photoetching development, as shown in fig. 2, etching the alumina film at the exposed part by means of phosphoric acid water bath heating, and cleaning the unexposed photoresist by means of acetone.

And fifthly, connecting the copper wire with the metal molybdenum layer exposed at the bottom of the side edge of the anvil by using silver paste, and curing for 2 hours at 150 ℃ to ensure firm contact.

Example 3: the experimental set-up and measurements are described with reference to FIGS. 3 and 4

As shown in fig. 3 and 4, 1 is a diamond anvil, 2 is a parallel plate electrode, 3 is a four-electrode, 4 is an alumina protective layer, 5 is a metal gasket, 6 is an insulating layer, 7 is a sample, and 8 is an electrode lead (8.1 is an electrode lead corresponding to the parallel plate electrode, and 8.2 is an electrode lead corresponding to the four-electrode); during assembly, the anvil surfaces of the two anvils are ensured to be parallel and in a concentric circle, the gasket is reset (the anvil is restored to be embedded into an indentation state), the sample and the ruby are filled in the sample cavity, then the gasket (containing the sample) is squeezed by the anvils to generate a high-pressure environment, and the experimental pressure is calibrated through the ruby (the fluorescence peak of the ruby is a function of the pressure) in the sample cavity.

The experimental measurement selects corresponding instrument devices according to different experimental needs: the parallel plate electrode 2 is matched with an alternating current frequency response analysis device, a parallel plate electrode lead wire of 8.1 is connected with an electrochemical impedance spectrometer, an impedance real part and an impedance imaginary part of a sample can be obtained under specified pressure through determination of alternating current voltage, frequency range and frequency resolution, equivalent circuit fitting is carried out on the impedance spectrometer by Zview software, parameters such as sample resistance (crystal grain/crystal boundary), relaxation frequency, relaxation time, relative dielectric constant and the like can be determined, and analysis of a conduction mechanism (electron/ion) is realized; the four-electrode 3 is matched with the direct current transport property measuring system, and the lead of the four-electrode 8.2 is connected with the Hall system. The influence of contact resistance can be eliminated through a Van der pol method, so that the accurate measurement of the resistivity is realized, meanwhile, by utilizing the Hall effect, a series of parameters such as the carrier concentration, the carrier mobility, the Hall coefficient, the magnetic resistance and the like of a sample can be obtained under the magnetic field environment, and finally, the effective description of the internal electromagnetic transport is realized.

Example 4: finite element analysis for experimental errors caused by different electrode sizes

The experimental configuration of the parallel plate electrode is a disc with the same upper and lower sizes, but the invention aims to realize a composite electrodeThe periphery of the disc electrode on one side is symmetrically etched with 4 windows, and the influence of the window size on experimental measurement needs to be researched. The present invention utilizes finite elements to address the above problems. The experimental simulation parameters are as follows: sample diameter 100 μm, sample thickness 20 μm (taking into account the loading of the experimental pressure), sample resistivity 1X 10⁴Omega cm (simulated semiconductor material), electrode thickness 2 μm, electrode resistivity 1X 10^-6Omega cm. Four windows are symmetrically etched around the circular electrode on the upper surface of the sample, four electrodes are arranged in the windows, 100 muV voltage is applied between the circular electrodes at the upper end and the lower end of the sample (polarization caused by overlarge potential difference is avoided), and the electric field intensity in the sample is analyzed, as shown in figure 5.

By varying the length of the side L of the etch window (the window is a square tangent to the circular electrode), experimental errors caused by the window size on the ac frequency response measurement can be analyzed, as shown in fig. 6. Experimental simulation shows that the window size of the parallel plate electrode is within 10 μm, and the experimental error is less than 3%. The size of an etched window of the composite electrode designed by the invention is 5 micrometers, so that experimental errors caused by the size of the electrode per se are within an acceptable range, and the feasibility of the composite electrode is proved.

Example 5: polycrystalline CaMoO₄Alternating current frequency response analysis of electrical parameters

An impedance spectrum instrument (Solartron 1260+1296) is used for carrying out alternating current frequency response measurement on a polycrystalline star sample, the applied alternating current voltage is 1V, the frequency range of 0.1Hz to 10MHz is selected, a plurality of points are selected within the pressure range of 0 to 25GPa for impedance measurement, and the measurement result is shown in figure 7. In order to further analyze more intrinsic mechanisms, Zview software is utilized, a group of parallel R-CPEs is adopted to perform equivalent circuit fitting on an impedance measurement result, and the intercept of an impedance arc and an abscissa after fitting is a sample resistance value, so that the change relation of sample grains and grain boundary resistance along with pressure can be obtained, as shown in figure 8.a, an impedance spectrum high-frequency region corresponds to the grain resistance, and a low-frequency region corresponds to the grain boundary resistance. Via M + M' + j M ″ -jwC₀Z formula (w is 2 pi f), the corresponding relation of M' -f can be obtained, and then the grain and grain boundary relaxation is determinedThe frequency as a function of pressure is shown in fig. 8. b. At the same time, according to epsilon_r＝Cd/ε₀S, the variation of the relative dielectric constant with pressure can be obtained as shown in FIG. 8. c.

Through the measurement of the above experiment, it can be seen that CaMoO₄The resistance, relaxation frequency and relative dielectric constant of the sample are discontinuously changed along with the pressure, and the structural phase change is really reported at the corresponding pressure point, so that the measurement of the electrical parameters under the high-voltage environment can be used as an effective technical means for analyzing the atomic displacement and the lattice framework change of the material, and the reliability of the composite electrode on the alternating-current frequency response analysis is further verified.

Example 6: polycrystalline MoO₂Direct current transport property measurement

MoO of the invention₂The measurement of resistivity and Hall effect at high voltage of the samples was performed using the eastern morning scene ET series test system, and the application and reading of voltage and current was performed using Keithley 2400+ 2700. The resistivity measurement is based on the Van der pol method of four electrodes, and the resistivity of the sample is represented by the formula

exp(-π·R_AB、CD·d/ρ)+exp(-π·R_BC、DA·d/ρ)＝1

Determining where d is the sample thickness, ρ is the sample resistivity, R_AB、CDDefined as the potential difference between AB divided by

Current between CDs, R_BC、DABC is defined as the potential difference between divided by the current between DA. Considering the DAC sample size (flat cylinder) and the spatial symmetry of the electrodes, the above formula can be simplified to

Experimental errors caused by contact resistance can be eliminated by van der pol method resistivity measurement, and the change relation of the resistivity of the sample under different pressure environments along with the pressure is shown in fig. 9. The Hall effect measurement is carried out in a 1T magnetic field environment, the four electrodes in the composite electrode are also adopted, the Hall coefficient, the carrier concentration and the carrier mobility of the sample can be obtained by reading the current, the voltage and the sample thickness, and the specific formula is as follows:

hall coefficientA carrier concentration ofWherein e is 1.6021892 × 10^-19C, carrier mobility ofThe change of the parameters along with the pressure is shown in figure 10, and the discontinuous change of the resistivity and Hall parameters of the sample along with the pressure can be found, and the abnormal change is also caused by the structural phase change of the sample under high pressure, so that the experimental result is consistent with the literature report no matter the alternating current frequency response analysis of the parallel plate electrode in the embodiment 5 or the direct current transport measurement of the four electrodes in the embodiment. The parallel plate electrode and the four electrodes in the composite electrode can realize the measurement of respective characteristics without mutual interference, and further realize the cooperative measurement of electromagnetic parameters in the whole field under high voltage.