CN111115588B - Spinning zero-energy-gap semiconductor material with zero energy gap protected by lattice symmetry and preparation method thereof - Google Patents
Spinning zero-energy-gap semiconductor material with zero energy gap protected by lattice symmetry and preparation method thereof Download PDFInfo
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Abstract
The invention relates to a spinning zero energy gap semiconductor material with zero energy gap protected by lattice symmetry and a preparation method thereof; material knotStructure d 0 -KCrZ alloy of the d-type half-Heusler; wherein Z = S, se or Te. Has a spin polarizability of 100% and a value of 5 mu B The integer molecular magnetic moment of (c). The KCrZ is prepared by adopting a heat treatment process combining ball milling, annealing and quenching; the method is simple and easy to realize, overcomes the defect that the cost is higher when the conventional methods such as magnetron sputtering, arc furnace smelting and the like are mostly adopted for preparing similar materials, and the prepared KCrZ series alloy has a stable phase, has a half Heusler structure, has stable zero-energy gap characteristics, is not easily influenced by external environmental factors to further damage the characteristics of a spinning zero-energy gap semiconductor, and is an ideal spinning zero-energy gap semiconductor material with a stable zero-energy gap.
Description
Technical Field
The invention relates to the technical field of materials, in particular to a spin zero-energy-gap semiconductor material applied to a novel spin electronic device, and a preparation method thereof.
Background
In recent years, the application of magnetic tunnel junctions to multifunctional spintronics devices with low power consumption and high operational speed has attracted increasing researchers' attention. Since the performance of spintronics devices is closely related to the spin polarizability of a material, it is necessary to seek a material with a high spin polarizability. So far, semi-metallic (hereinafter abbreviated as HM) materials having a spin polarizability of 100% have been discovered in succession, and are of great interest in the application of spintronics devices. The Heusler alloy and the half Heusler alloy are used as HM materials, have the characteristics of high Curie temperature, easiness in preparation and the like, and arouse the enthusiasm for searching high-spin polarization materials in the Heusler alloy.
Heretofore, a particular class of spintronics materials in the Heusler family, spin zero bandgap semiconductor materials, has emerged whose band structure is characterized by the presence of a semiconductor or insulator bandgap in one spin direction at the fermi surface, which is within the semiconductor bandgap; while in the other spin direction there is a zero energy gap at the fermi surface, i.e. the conduction and valence bands are cut exactly at the fermi level. This allows the carriers to be fully spin-polarized and to have extremely high mobility, which is of great advantage in spintronics devices. The spin zero-energy-gap semiconductor not only has 100% of high spin polarizability peculiar to the semimetal material, but also combines the advantages of the semiconductor material, has wide application prospect, and can be used as an ideal spin injection and transport material instead of the semimetal material. However, to date, the following problems are faced in this field: first, the problem of stability of the zero-gap semiconductor is an important basic problem that currently hinders the push of the material to practical applications. The zero energy gap of the spin zero energy gap semiconductor material discovered in the current experiment and theory is basically formed by two groups of energy bands (top of valence band and bottom of conduction band) under different degeneracy in a tangent mode at the Fermi surface, so that the generated zero energy gap structure is very unstable, and in the actual preparation process, the zero energy gap of the spin zero energy gap semiconductor material is likely to disappear due to the fact that the two groups of energy bands are further overlapped or opened, and the original characteristics of the spin zero energy gap semiconductor material are damaged; secondly, due to the preparation process conditions and environmental conditions, such as temperature rise and the like, various chaotic space occupying defects and lattice distortion can also exist in the material in the preparation process, so that the zero energy gap structure of the spin zero energy gap semiconductor material is damaged, and the physical properties of the material are further damaged. The above two points are very unfavorable for the preparation and application of the current spin zero-energy gap semiconductor material, so that although the spin zero-energy gap semiconductor material is an ideal material in the application field of the current novel spin electronic device, such as spin injection, the actual preparation and application are very hindered, and therefore, the selection of the spin zero-energy gap semiconductor material with a stable zero-energy gap structure is very necessary and critical.
Disclosure of Invention
The invention aims to solve the problems that: the problem of unstable zero energy gap of the current spinning zero energy gap semiconductor material is solved, and a theoretical design model of the spinning zero energy gap semiconductor material with the stable zero energy gap protected by lattice symmetry and a preparation method of the material are provided.
The technical scheme of the invention is as follows:
a spin zero-gap semiconductor material having a zero-gap protected by lattice symmetry; it is characterized in that the structure is d 0 -KCrZ alloy of the type d half-Heusler; wherein Z = S, se or Te.
The semiconductor material has 100% spin polarizability and 5 mu B The integral number of molecular magnetic moments.
The invention relates to a preparation method of a spin zero-energy gap semiconductor material with a zero-energy gap protected by lattice symmetry, which comprises the following steps:
1) Mixing K powder, cr powder and Z powder according to a mol ratio of 1:1:1, mixing the mixture in a sealed stainless steel or agate ball-milling tank, and simultaneously selecting three stainless steel balls or agate balls with different specifications, namely large, medium and small, with the diameters of 5-12 mm according to the ratio of 1:2:2, placing the mixture into a stainless steel or agate tank, wherein the ball-to-material ratio is 8-20: 1;
2) Vacuumizing a ball milling tank at room temperature, performing ball milling on a planetary ball mill in an argon atmosphere, wherein the rotating speed of the ball mill is 500-700 r/min, the ball milling time is 8-20 hours in total, and stopping the ball milling for half an hour and cooling the ball milling for half an hour within the ball milling period of 8-20 hours;
3) Placing the ball-milled powder sample in a grinding tool, keeping the pressure of the grinding tool at 250-350 MPa for 5-10 minutes, and finally pressing the powder sample into a sheet shape;
4) Placing the pressed sample in a tubular annealing furnace, vacuumizing a quartz vacuum tube by using a molecular pump, and then filling argon for protection, wherein the annealing heat preservation temperature is set to be 380-600 ℃, and the heat preservation sintering time is 36-48 hours;
5) And (3) putting the pressed KCrZ sample obtained in the step (3) back into the ball milling tank again, putting the grinding balls into the ball milling tank according to the ball material ratio in the step (1) and the quantity ratio of the grinding balls with different specifications, repeating the ball milling process in the step (2), then pressing the KCrZ powder sample obtained by re-grinding according to the step (3), putting the pressed KCrZ powder sample into a tubular annealing furnace, repeating the annealing and sintering process in the step (4), repeating the processes for 3-5 times, finally taking out the sample, putting the sample into liquid nitrogen for quenching, and cooling to obtain the pure KCrZ polycrystalline sample.
The purity of the K powder, the Cr powder and the Z powder is more than 99.99 percent.
The ball material ratio is 15:1.
the ball milling time of the step 2) is 8-20 hours, preferably, the clockwise milling time is 4-10 hours, and the anticlockwise milling time is 4-10 hours.
For KCrS in the step 2), the preferred ball milling time is 12-16 hours, wherein the ball milling is carried out for 6-8 hours clockwise, and then the ball milling is carried out for 6-8 hours anticlockwise; for KCrSe, the ball milling time is preferably 10 to 14 hours, wherein the ball milling is carried out for 5 to 7 hours in a clockwise manner, and then the ball milling is carried out for 5 to 7 hours in a counterclockwise manner; for KCrTe, the preferred ball milling time is 14 to 18 hours, with 7 to 9 hours clockwise followed by 7 to 9 hours counter clockwise.
In the step 3), for KCrS, the preferred annealing heat preservation temperature is set to be 400-500 ℃; for KCrSe, the annealing heat preservation temperature is preferably set to be 380-450 ℃; for KCrTe, the annealing temperature is preferably set to 500-600 ℃.
The step 4) is preferably put into 77K liquid nitrogen for quenching for 15 to 25 seconds.
The concrete description is as follows:
the invention specifically relates to three types of d 0 KCrS, KCrSe and KCrTe alloys of type-d half-Heusler structure. The series of materials have 100% spin polarizability and ultra-large integral number molecular magnetic moment (5 mu) B ) Meanwhile, different from the traditional spinning zero-energy-gap semiconductor material (the zero-energy-gap of the traditional spinning zero-energy-gap semiconductor material is formed by two groups of energy bands which are tangent at the fermi surface), the zero-energy-gap of the traditional spinning zero-energy-gap semiconductor material comes from a group of multiple degenerated energy bands formed under a certain specific crystal field, one of the multiple degenerated energy bands is formed in a 'turning' mode, and the fermi surface is just in the band gap.
One class belongs to 0 -three alloys of the type d half-Heusler structure: KCrZ (Z = S, se, te), wherein the outermost valence electron of the metal element K is 4S 1 D orbital has no electron occupancy, i.e. d 0 Belonging to the alkali metal elements; the electron arrangement of the metal element Cr as the outermost layer is 3d 5 4s 1 Belonging to transition metal elements; z is a sixth main group element S, se or Te. The material is a novel spinning zero-energy-gap semiconductor material with a particularly stable zero-energy-gap, and the energy band structure of the material has the characteristics that: for one of the spin directions, there is a semiconductor bandgap near the fermi surface, and the fermi surface is within the bandgap; for the other spin direction, at the Fermi surfaceThe zero energy gap with the width of zero exists, and is formed by a group of multiple degenerated energy bands under a specific crystal field, one of the multiple degenerated energy bands is turned over, and the Fermi plane is just in the zero energy gap, and the zero energy gap with the characteristics is very stable due to the protection of the specific crystal field because the zero energy gap is generated from one group of degenerated energy bands instead of two groups of energy bands which are formed in a tangent mode at the Fermi plane, so that an effective method is provided for solving the problem of instability of the zero energy gap of the traditional spinning zero-band-gap semiconductor material.
In the invention, three kinds of spin zero energy gap semiconductor materials with zero energy gap protected by lattice symmetry, namely KCrZ (Z = S, se, te) are prepared by adopting a heat treatment process combining ball milling with annealing and quenching, and the outstanding substantive characteristics are as follows:
(1) Aiming at the problem that the spin zero-energy-gap semiconductor has a stable zero-energy gap which is the most important basic condition to be pushed to practical application, the zero-energy gap of the material is broken and destroyed in the practical preparation process due to the influence of external environment, such as thermal disturbance caused by temperature rise and structural defects brought by surface and impurities, so that an ideal spin zero-energy-gap semiconductor material cannot be synthesized, and the physical properties of the material are further influenced, compared with the traditional spin zero-energy-gap semiconductor material, the spin zero-energy-gap semiconductor material protected by lattice symmetry has the advantages that the zero-energy gap in a certain spin direction is derived from a group of multiple energy bands under a certain specific crystal field, one of the energy bands is turned to form a zero-energy gap, and the Fermi plane is just in the formed zero-energy gap degeneracy; for the other spin direction, the fermi surface is in the band gap of a certain width formed between the valence band top and the conduction band bottom. The zero energy gap formed in the way is very stable because of the protection of a specific crystal field, and is a novel spin zero energy gap semiconductor material with the zero energy gap protected by lattice symmetry, the design and implementation of the material are very beneficial to the practical preparation and application of the future spin zero energy gap semiconductor material, a direct and effective means is provided for solving the problem of unstable current zero energy gap structure, and the key problem that the current spin zero energy gap semiconductor material is prevented from being pushed to practical application is solved;
(2) Aiming at the problem that the zero energy gap characteristic of the spin zero energy gap semiconductor material is damaged due to various disordered occupancy defects and lattice distortion in the preparation process possibly caused by the conditions of the current preparation process, the invention discloses a spin zero energy gap semiconductor material protected by lattice symmetry, wherein the KCrS, KCrSe and KCrTe materials are relatively large in the existence of the disordered occupancy defects among atoms and the cubic and tetragonal lattice distortion within the range of-10%, and the spin zero energy gap semiconductor characteristic of the material is not influenced, namely when the anti-occupancy defects among atoms and the lattice distortion among the materials to a large extent exist, the material can still keep the spin zero energy gap semiconductor characteristic, so that the harsh requirements of the materials on the preparation process are reduced, the actual preparation and application of the materials are very favorable, and the series of materials become an ideal novel spintronics material with important application value.
(3) The method for preparing the KCrZ series alloy by combining the material ball milling method with the heat treatment process is simple and easy to realize, overcomes the defect that the cost is higher when the conventional similar material is prepared by adopting methods such as magnetron sputtering, arc furnace smelting and the like, and the prepared KCrZ series alloy has stable phase, a half Heusler structure and stable zero-energy gap characteristic, is not easily influenced by external environmental factors to further damage the characteristics of a spinning zero-energy gap semiconductor, and is an ideal spinning zero-energy gap semiconductor material with stable zero-energy gap.
Drawings
The invention is further illustrated with reference to the following figures and examples.
FIG. 1 is a schematic diagram of a band structure of a spin zero-gap semiconductor material with a zero-gap protected by lattice symmetry.
FIG. 2 (a) is a spin zero-gap semiconductor material d with zero-gap protected by lattice symmetry 0 -a lattice structure diagram of KCrS of the d-type half-Heusler structure;
FIG. 2 (b) spin zero-gap semiconductor material d with zero-gap protected by lattice symmetry 0 -a lattice structure diagram of KCrSe of the d-type half-Heusler structure;
FIG. 2 (c) spin zero-gap semiconductor material d with zero-gap protected by lattice symmetry 0 -a lattice structure diagram of KCrTe of type d half-Heusler structure;
FIG. 3 (a) is the spin-up band structure of a spin zero-gap semiconductor material KCrS protected by lattice symmetry, in which t is a triple degenerate t 2g Two tracks are arranged at the top of the valence band, one track is inverted to the bottom of the conduction band, and the two tracks are tangent to the Fermi level at a point G to form a zero energy gap;
fig. 3 (b) is a spin-down direction band structure of a spin zero-gap semiconductor material KCrS protected by lattice symmetry with a large band gap as wide as 2.99eV near the fermi surface.
FIG. 4 (a) is the spin-up band structure of a spin zero-gap semiconductor material KCrSe protected by lattice symmetry, in which t is a triple degenerated 2g Two orbitals are arranged at the top of the valence band, one orbit is inverted to the bottom of the conduction band, and a zero energy gap is formed at the G point phase and the Fermi level;
fig. 4 (b) is a spin-down direction band structure of a spin zero-gap semiconductor material KCrSe protected by lattice symmetry, with a large band gap as wide as 2.86 eV.
FIG. 5 (a) is the spin-up band structure of a spin zero-gap semiconductor material KCrTe protected by lattice symmetry with a threefold degenerate t 2g Two tracks are arranged at the top of the valence band, one track is inverted to the bottom of the conduction band, and the two tracks are tangent to the Fermi level at a point G to form a zero energy gap;
fig. 5 (b) is a spin-down band structure of a spin zero-gap semiconductor material KCrTe protected by lattice symmetry, with a large band gap of 3.12 eV.
Detailed Description
The embodiment of the invention provides the following technical scheme that the spin zero-energy-gap semiconductor material has a zero-energy gap protected by lattice symmetry; it is characterized in that the structure is d 0 -KCrZ alloy of the type d half-Heusler; wherein Z =The semiconductor material of S, se or Te has a spin polarizability of 100% and a value of 5 mu B The integral number of molecular magnetic moments.
Example 1
Preparation d 0 -d-type KCrS half-Heusler structured spin zero-energy gap semiconductor material. The specific process comprises the following steps:
the KCrS alloy polycrystalline material is prepared by adopting a ball milling method.
Step 1: according to the mol ratio of 1:1:1, weighing 60g of K powder, cr powder and S powder with the purity of 99.999 percent, mixing the K powder, the Cr powder and the S powder in a sealed stainless steel ball-milling tank, wherein the diameter of the ball-milling tank is 80mm, and simultaneously, mixing stainless steel balls or agate balls with the diameters of 5mm, 8mm and 12mm according to the ratio of 1:2:2, placing the mixture into a stainless steel or agate tank, wherein the ball-to-material ratio (the weight ratio of grinding balls to K, cr and S materials) is 15:1;
step 2: sealing the ball milling tank, opening an exhaust valve, vacuumizing the ball milling tank, introducing argon to form protective gas to prevent oxidation, carrying out ball milling on a planetary ball mill under the argon atmosphere, wherein the process conditions for carrying out ball milling are that the rotating speed is set to be 500 revolutions per minute, carrying out ball milling for 6 hours clockwise at room temperature, and then carrying out ball milling for 6 hours anticlockwise, wherein the rotating speed of the ball mill is very high, the ball milling is stopped and cooled for half an hour every half an hour in order to prevent overheating, and the total grinding time is 12 hours;
and 3, step 3: putting the powder sample obtained in the step (3) into a grinding tool, pressing the powder into a cylindrical slice with the height of 3mm and the diameter of 10mm under the pressure of 250MPa, and keeping the sample powder in the pressing tool for 10 minutes under the pressure of 250MPa in the pressing process to prevent the sample after pressing from being broken or falling off due to air holes in the pressed sample;
and 4, step 4: placing the tabletted sample in a tubular annealing furnace for heat preservation, vacuumizing a quartz vacuum tube by using a molecular pump until the vacuum degree is less than 1 multiplied by 10 -6 Pa, then filling argon for protection, setting the temperature of the tubular annealing furnace at 400 ℃, the heating rate at 2 ℃/min, and carrying out heat preservation sintering on the sample at 500 ℃ for 48 hours;
and 5, step 5: and (3) putting the tabletting KCrS sample obtained in the step (4) back into the ball milling tank, and simultaneously, adding the mixture of the mixture 1:2:2 stainless steel balls or agate balls with the number ratio of 5mm, 8mm and 12mm, repeating the ball milling process in the step 2, then tabletting the KCrS powder sample obtained by re-grinding in the step 3, then placing the sample in a tubular annealing furnace again, repeating the annealing sintering process in the step 4, repeating the processes for 3 times, wherein the KCrS powder subjected to heat preservation sintering in the steps 2-4 basically forms a required phase structure, but the uniformity is poor, so that the material phase is more uniform by performing ball milling and sintering for 3 times, finally taking out the sample, putting the sample into liquid nitrogen (77K) for quenching for 15 seconds, and cooling to obtain the pure KCrS polycrystalline sample.
The KCrS polycrystalline material prepared by the method is a novel spinning zero-energy-gap semiconductor material with stable zero energy gap, and the energy gap with the width of zero is a group of three merged t 2g The energy band is formed after being turned, and for the material, the Fermi surface is just positioned in the formed zero energy gap, and compared with a common spinning zero energy gap semiconductor material, the generated zero energy gap is very stable because of the protection of a specific crystal field, and the technical problems that the zero energy gap in the field of the current spinning zero energy gap semiconductor material is very unstable and is not beneficial to the practical application of the material are solved. The lattice structure is shown in fig. 1, and the resulting band structure is shown in fig. 2.
FIG. 2 (a) is a view showing a structure of a crystal lattice of a KCrS polycrystalline sample (Z = S) having a half-Heusler structure obtained in this example;
FIG. 3 is a diagram showing the band structure of a KCrS polycrystalline sample having a half-Heusler structure obtained in this example. It can be seen from the figure that it has a band gap with a width of up to 3.8eV in the spin down direction and a band gap with a width of zero in the spin up direction and the fermi surface is exactly in the zero band gap, in particular, the zero band gap is generated not by two sets of energy bands tangent at the fermi surface but by a set of 3-fold degenerate energy bands formed under the cubic crystal field, one of which is turned up to form, and it is due to the band characteristics that its zero band gap characteristics will be very stable.
Example 2
The KCrS alloy polycrystalline material is prepared by adopting a ball milling method.
Step 1: according to a mol ratio of 1:1:1, weighing 70g of K powder, cr powder and S powder with the purity of 99.999 percent, mixing the powder and the powder in a sealed stainless steel ball milling tank, wherein the diameter of the ball milling tank is 80mm, and simultaneously, mixing stainless steel balls or agate balls with the diameters of 5mm, 8mm and 12mm according to the ratio of 1:2:2, placing the mixture into a stainless steel or agate tank, wherein the ball-to-material ratio (the weight ratio of grinding balls to K, zr and S materials) is 15:1;
step 2: sealing the ball milling tank, opening an exhaust valve, vacuumizing the ball milling tank, introducing argon to form protective gas to prevent oxidation, carrying out ball milling on a planetary ball mill under the argon atmosphere, wherein the process conditions for carrying out ball milling are that the rotating speed is set to be 500 revolutions per minute, carrying out ball milling for 7 hours clockwise at room temperature, and then carrying out ball milling for 7 hours anticlockwise, wherein the rotating speed of the ball mill is very high, so that overheating is prevented in the ball milling process, the ball milling is stopped and cooled for half an hour every half an hour, and the total grinding time is 14 hours;
and 3, step 3: putting the powder sample obtained in the step (3) into a grinding tool, pressing the powder into a cylindrical slice with the height of 3mm and the diameter of 10mm under the pressure of 300MPa, and keeping the sample powder in the pressing tool for 8 minutes under the pressure of 300MPa in the pressing process to prevent the sample after pressing from being broken or falling off due to air holes;
and 4, step 4: placing the tabletted sample in a tubular annealing furnace for heat preservation, vacuumizing a quartz vacuum tube by using a molecular pump until the vacuum degree is less than 1 multiplied by 10 -6 Pa, then filling argon for protection, setting the temperature of the tubular annealing furnace at 450 ℃, the heating rate at 2 ℃/min, and carrying out heat preservation sintering on the sample at 450 ℃ for 42 hours;
and 5, step 5: and (3) putting the tabletting KCrS sample obtained in the step (4) back into the ball milling tank, and simultaneously, adding the mixture of the mixture 1:2:2 stainless steel balls or agate balls with the quantity ratio of 5mm, 8mm and 12mm, repeating the ball milling process in the step 2, then tabletting the KCrS powder sample obtained by re-grinding in the step 3, then placing the sample in a tubular annealing furnace again, repeating the annealing sintering process in the step 4, repeating the processes for 4 times, basically forming the required phase structure by the KCrS powder subjected to heat preservation sintering in the steps 2-5, but the uniformity is poor, so that the material phase is more uniform by performing ball milling and sintering for 4 times, finally taking out the sample, putting the sample into liquid nitrogen (77K) for quenching for 20 seconds, and cooling to obtain the pure KCrS polycrystalline sample.
FIG. 2 (a) is a view showing a structure of a crystal lattice of a KCrS polycrystalline sample (Z = S) having a half-Heusler structure obtained in this example;
FIG. 3 is a diagram showing the band structure of a KCrS polycrystalline sample having a half-Heusler structure obtained in this example.
Example 3
The KCrS alloy polycrystalline material is prepared by adopting a ball milling method.
Step 1: according to a mol ratio of 1:1:1, weighing 40g of K powder, cr powder and S powder with the purity of 99.999 percent, mixing the K powder, the Cr powder and the S powder in a sealed agate ball milling tank, wherein the diameter of the ball milling tank is 80mm, and simultaneously, stainless steel balls or agate balls with the diameters of 5mm, 8mm and 12mm are mixed according to the ratio of 1:2:2, placing the mixture into a stainless steel or agate tank, wherein the ball-to-material ratio (the weight ratio of grinding balls to K, zr and S materials) is 15:1;
step 2: sealing the ball milling tank, opening an exhaust valve, vacuumizing the ball milling tank, introducing argon to form protective gas to prevent oxidation, and performing ball milling on a planetary ball mill under the argon atmosphere under the process conditions that the rotating speed is set to be 500 revolutions per minute, performing clockwise ball milling for 8 hours at room temperature, and performing anticlockwise ball milling for 8 hours, wherein the rotating speed of the ball mill is very high, so that overheating is prevented in the ball milling process, the ball milling is stopped for half an hour and cooled, and the total grinding time is 16 hours;
and 3, step 3: putting the powder sample obtained in the step 3 into a grinding tool, pressing the powder into a cylindrical slice with the height of 3mm and the diameter of 10mm under the pressure of 350MPa, and keeping the sample powder in the pressing tool for 5 minutes under the pressure of 350MPa in the pressing process to prevent the sample after pressing from being broken or falling due to air holes;
and 4, step 4: placing the tabletted sample in a tubular annealing furnace for heat preservation, vacuumizing a quartz vacuum tube by using a molecular pump until the vacuum degree is less than 1 multiplied by 10 -6 Pa, then filling argon for protection, setting the temperature of the tubular annealing furnace at 500 ℃, the heating rate at 2 ℃/min, and carrying out heat preservation and burning on the sample at the temperature of 500 DEG CKnot for 36 hours;
and 5, step 5: and (5) putting the tabletting KCrS sample obtained in the step (4) back into the ball milling tank, and simultaneously, according to the step (1): 2:2 stainless steel balls or agate balls with the quantity ratio of 5mm, 8mm and 12mm, repeating the ball milling process in the step 2, then tabletting the KCrS powder sample obtained by re-grinding in the step 3, then placing the sample in a tubular annealing furnace again, repeating the annealing sintering process in the step 4, repeating the processes for 5 times, basically forming the required phase structure by the KCrS powder subjected to heat preservation sintering in the steps 2-5, but the uniformity is poor, so that the material phase is more uniform by performing ball milling and sintering for 5 times, finally taking out the sample, putting the sample into liquid nitrogen (77K) for quenching for 25 seconds, and cooling to obtain the pure KCrS polycrystalline sample.
FIG. 2 (a) is a view showing a structure of a crystal lattice of a KCrS polycrystalline sample (Z = S) having a half-Heusler structure obtained in this example;
FIG. 3 is a diagram showing the band structure of a KCrS polycrystalline sample having a half-Heusler structure obtained in this example.
Example 4
Preparation d 0 -a KCrSe spin zero-energy gap semiconductor material with a d-type half-Heusler structure. The specific process comprises the following steps:
the KCrSe alloy polycrystalline material is prepared by adopting a ball milling method.
Step 1: according to the mol ratio of 1:1:1, weighing 65g of K powder, cr powder and Se powder with the purity of 99.999 percent, mixing the K powder, the Cr powder and the Se powder in a sealed stainless steel ball-milling tank, wherein the diameter of the ball-milling tank is 80mm, and simultaneously, mixing stainless steel balls or agate balls with the diameters of 5mm, 8mm and 12mm according to the ratio of 1:2:2, placing the mixture into a stainless steel or agate tank, wherein the ball-to-material ratio (the weight ratio of grinding balls to K, zr and Se materials) is 15:1;
step 2: sealing the ball milling tank, opening an exhaust valve, vacuumizing the ball milling tank, introducing argon to form protective gas to prevent oxidation, carrying out ball milling on a planetary ball mill under the argon atmosphere, wherein the process conditions for carrying out ball milling are that the rotating speed is set to be 500 revolutions per minute, carrying out ball milling for 5 hours clockwise at room temperature, and then carrying out ball milling for 5 hours anticlockwise, wherein the rotating speed of the ball mill is very high, the ball milling is stopped for half an hour for cooling every half an hour, and the ball milling is carried out for 10 hours in total;
and 3, step 3: putting the powder sample obtained in the step (3) into a grinding tool, pressing the powder into a cylindrical slice with the height of 3mm and the diameter of 10mm under the pressure of 250MPa, and keeping the sample powder in the pressing tool for 10 minutes under the pressure of 250MPa in the pressing process to prevent the sample after pressing from being broken or falling off due to air holes in the pressed sample;
and 4, step 4: placing the tabletted sample in a tubular annealing furnace for heat preservation, vacuumizing a quartz vacuum tube by using a molecular pump until the vacuum degree is less than 1 multiplied by 10 -6 Pa, then filling argon for protection, setting the temperature of the tubular annealing furnace to be 380 ℃, the heating rate to be 2 ℃/min, and carrying out heat preservation sintering on the sample at the temperature of 380 ℃ for 48 hours;
and 5, step 5: and (5) putting the tabletting KCrSe sample obtained in the step (4) back into the ball milling tank, and simultaneously, according to the step (1): 2:2 stainless steel balls or agate balls with the number ratio of 5mm, 8mm and 12mm, repeating the ball milling process in the step 2, then tabletting the KCrSe powder sample obtained by re-grinding in the step 3, then placing the sample in a tubular annealing furnace again, repeating the annealing sintering process in the step 4, repeating the processes for 5 times, basically forming the required phase structure by the KCrSe powder subjected to heat preservation sintering in the steps 2-5, but the uniformity is poor, so that the material phase is more uniform by performing ball milling and sintering for 5 times, finally taking out the sample, putting the sample into liquid nitrogen (77K) for quenching for 25 seconds, and cooling to obtain the pure KCrSe polycrystal sample.
In this way, a KCrSe polycrystalline material was prepared, the lattice structure of which is shown in fig. 2 (b) (Z = Se). FIG. 4 is a diagram showing the band structure of a polycrystalline KCrSe material prepared in this example, which is a spin zero-gap semiconductor material having a zero-gap protected by lattice symmetry, as with KCrS prepared in example 1.
Example 5
Preparation d 0 -a KCrSe spin zero-energy gap semiconductor material with a d-type half-Heusler structure. The specific process comprises the following steps:
the KCrSe alloy polycrystalline material is prepared by adopting a ball milling method.
Step 1: according to the mol ratio of 1:1: weighing 75g of K powder, cr powder and Se powder with the purity of 99.999 percent, mixing the K powder, the Cr powder and the Se powder in a sealed stainless steel ball milling tank, wherein the diameter of the ball milling tank is 80mm, and simultaneously, mixing stainless steel balls or agate balls with the diameters of 5mm, 8mm and 12mm according to the ratio of 1:2:2, placing the mixture into a stainless steel or agate tank, wherein the ball-to-material ratio (the weight ratio of grinding balls to K, zr and Se materials) is 15:1;
step 2: sealing the ball milling tank, opening an exhaust valve, vacuumizing the ball milling tank, introducing argon to form protective gas to prevent oxidation, carrying out ball milling on a planetary ball mill under the argon atmosphere, wherein the process conditions for carrying out ball milling are that the rotating speed is set to be 500 revolutions per minute, carrying out ball milling for 6 hours clockwise at room temperature, and then carrying out ball milling for 6 hours anticlockwise, wherein the rotating speed of the ball mill is very high, the ball milling is stopped and cooled for half an hour every half an hour in order to prevent overheating, and the total grinding time is 12 hours;
and 3, step 3: putting the powder sample obtained in the step (3) into a grinding tool, pressing the powder into a cylindrical slice with the height of 3mm and the diameter of 10mm under the pressure of 300MPa, and keeping the sample powder in the pressing tool for 8 minutes under the pressure of 300MPa in the pressing process to prevent the sample after pressing from being broken or falling off due to air holes;
and 4, step 4: placing the tabletted sample in a tube annealing furnace for heat preservation, vacuumizing a quartz vacuum tube by using a molecular pump until the vacuum degree is less than 1 multiplied by 10 -6 Pa, then filling argon for protection, setting the temperature of a tubular annealing furnace to be 415 ℃, the heating rate to be 2 ℃/min, and carrying out heat preservation sintering on the sample at the temperature of 415 ℃ for 42 hours;
and 5, step 5: and (5) putting the tabletting KCrSe sample obtained in the step (4) back into the ball milling tank, and simultaneously, according to the step (1): 2:2 stainless steel balls or agate balls with the number ratio of 5mm, 8mm and 12mm, repeating the ball milling process in the step 2, then tabletting the KCrSe powder sample obtained by re-grinding in the step 3, then placing the sample in a tubular annealing furnace again, repeating the annealing sintering process in the step 4, repeating the processes for 4 times, basically forming the required phase structure by the KCrSe powder subjected to heat preservation sintering in the steps 2-5, but the uniformity is poor, so that the material phase is more uniform by performing ball milling and sintering for 4 times, finally taking out the sample, putting the sample into liquid nitrogen (77K) for quenching for 20 seconds, and cooling to obtain the pure KCrSe polycrystal sample.
In this way, a KCrSe polycrystalline material was prepared, the lattice structure of which is shown in fig. 2 (b) (Z = Se). FIG. 4 is a diagram showing the band structure of a polycrystalline KCrSe material prepared in this example, which is a spin zero-gap semiconductor material having a zero-gap protected by lattice symmetry, as with KCrS prepared in example 1.
Example 6
Preparation d 0 -a KCrSe spin zero-energy gap semiconductor material of a d-type half-Heusler structure. The specific process comprises the following steps:
the KCrSe alloy polycrystalline material is prepared by adopting a ball milling method.
Step 1: according to the mol ratio of 1:1: weighing 35g of K powder, cr powder and Se powder with the purity of 99.999 percent, mixing in a sealed agate ball-milling tank with the diameter of 80mm, and simultaneously mixing stainless steel balls or agate balls with the diameters of 5mm, 8mm and 12mm according to the weight ratio of 1:2:2, placing the mixture into a stainless steel or agate tank, wherein the ball-to-material ratio (the weight ratio of grinding balls to K, zr and Se materials) is 15:1;
step 2: sealing the ball milling tank, opening an exhaust valve, vacuumizing the ball milling tank, introducing argon to form protective gas to prevent oxidation, and performing ball milling on a planetary ball mill under the argon atmosphere under the process conditions that the rotating speed is set to be 500 revolutions per minute, performing clockwise ball milling for 7 hours at room temperature, and performing anticlockwise ball milling for 7 hours, wherein the rotating speed of the ball mill is very high, so that overheating is prevented in the ball milling process, the ball milling is stopped for half an hour and cooled, and the total grinding time is 14 hours;
and 3, step 3: putting the powder sample obtained in the step 3 into a grinding tool, pressing the powder into a cylindrical slice with the height of 3mm and the diameter of 10mm under the pressure of 350MPa, and keeping the sample powder in the pressing tool for 5 minutes under the pressure of 350MPa in the pressing process to prevent the sample after pressing from being broken or falling due to air holes in the pressed sample;
and 4, step 4: placing the tabletted sample in a tubular annealing furnace for heat preservation, and pumping a quartz vacuum tube by using a molecular pumpVacuum pumping to a vacuum degree of less than 1 × 10 -6 Pa, then filling argon for protection, setting the temperature of the tubular annealing furnace to be 450 ℃, the heating rate to be 2 ℃/min, and carrying out heat preservation sintering on the sample at the temperature of 450 ℃ for 36 hours;
and 5, step 5: and (5) putting the tabletting KCrSe sample obtained in the step (4) back into the ball milling tank, and simultaneously, according to the step (1): 2:2 stainless steel balls or agate balls with the quantity ratio of 5mm, 8mm and 12mm, repeating the ball milling process in the step 2, then tabletting the KCrSe powder sample obtained by re-grinding in the step 3, then placing the sample in a tubular annealing furnace again, repeating the annealing sintering process in the step 4, repeating the processes for 3 times, basically forming the required phase structure by the KCrSe powder subjected to heat preservation sintering in the steps 2-5, but the uniformity is poor, so that the material phase is more uniform by performing ball milling and sintering for 3 times, finally taking out the sample, putting the sample into liquid nitrogen (77K) for quenching for 15 seconds, and cooling to obtain the pure KCrSe polycrystal sample.
In this way, a KCrSe polycrystalline material was prepared, the lattice structure of which is shown in fig. 2 (b) (Z = Se). FIG. 4 is a diagram showing the band structure of a polycrystalline KCrSe material prepared in this example, which is a spin zero-gap semiconductor material having a zero-gap protected by lattice symmetry, as with KCrS prepared in example 1.
Example 7
Preparation d 0 -a KCrTe spin zero-energy gap semiconductor material with a d-type half-Heusler structure. The specific process comprises the following steps:
the KCrTe alloy polycrystalline material is prepared by adopting a ball milling method.
Step 1: according to a mol ratio of 1:1:1, weighing 70g of K powder, cr powder and Te powder with the purity of 99.999 percent, mixing the powder and the powder in a sealed stainless steel ball-milling tank, wherein the diameter of the ball-milling tank is 80mm, and simultaneously, mixing stainless steel balls or agate balls with the diameters of 5mm, 8mm and 12mm according to the ratio of 1:2:2, placing the mixture into a stainless steel or agate tank, wherein the ball-to-material ratio (the weight ratio of grinding balls to K, zr and Te materials) is 15:1;
step 2: sealing the ball milling tank, opening an exhaust valve, vacuumizing the ball milling tank, introducing argon to form protective gas to prevent oxidation, and performing ball milling on a planetary ball mill under the argon atmosphere under the process conditions that the rotating speed is set to be 500 revolutions per minute, performing clockwise ball milling for 7 hours at room temperature, and performing anticlockwise ball milling for 7 hours, wherein the rotating speed of the ball mill is very high, so that overheating is prevented in the ball milling process, the ball milling is stopped for half an hour and cooled, and the total grinding time is 14 hours;
and 3, step 3: putting the powder sample obtained in the step (3) into a grinding tool, pressing the powder into a cylindrical slice with the height of 3mm and the diameter of 10mm under the pressure of 250MPa, and keeping the sample powder in the pressing tool for 10 minutes under the pressure of 250MPa in the pressing process to prevent the sample after pressing from being broken or falling off due to air holes in the pressed sample;
and 4, step 4: placing the tabletted sample in a tubular annealing furnace for heat preservation, vacuumizing a quartz vacuum tube by using a molecular pump until the vacuum degree is less than 1 multiplied by 10 -6 Pa, then filling argon for protection, setting the temperature of the tubular annealing furnace at 600 ℃, the heating rate at 2 ℃/min, and carrying out heat preservation sintering on the sample at 500 ℃ for 48 hours;
and 5, step 5: and (5) putting the tabletting KCrTe sample obtained in the step (4) back into the ball milling tank, and simultaneously, according to the step (1): 2:2 stainless steel balls or agate balls with the quantity ratio of 5mm, 8mm and 12mm, repeating the ball milling process in the step 2, then tabletting the KCrTe powder sample obtained by re-grinding in the step 3, then placing the sample in a tubular annealing furnace again, repeating the annealing sintering process in the step 4, repeating the processes for 5 times, basically forming the required phase structure by the KCrTe powder subjected to heat preservation sintering in the steps 2-5, but the uniformity is poor, so that the material phase is more uniform by performing ball milling and sintering for 5 times, finally taking out the sample, putting the sample into liquid nitrogen (77K) for quenching for 25 seconds, and cooling to obtain the pure KCrTe polycrystal sample.
In this way, a KCrTe polycrystalline material was produced, the lattice structure of which is shown in fig. 2 (c) (Z = Te). FIG. 5 is a diagram showing the band structure of a polycrystalline material of KCrTe obtained in the present example, which is a spin zero-gap semiconductor material having a zero-gap protected by lattice symmetry, like KCrS obtained in example 1.
Example 8
Preparation d 0 -a KCrTe spin zero-energy gap semiconductor material with a d-type half-Heusler structure. The specific process comprises the following steps:
the KCrTe alloy polycrystalline material is prepared by adopting a ball milling method.
Step 1: according to the mol ratio of 1:1:1, weighing 75g of K powder, cr powder and Te powder with the purity of 99.999 percent, mixing the K powder, the Cr powder and the Te powder in a sealed stainless steel ball-milling tank, wherein the diameter of the ball-milling tank is 80mm, and simultaneously, mixing stainless steel balls or agate balls with the diameters of 5mm, 8mm and 12mm according to the ratio of 1:2:2, placing the mixture into a stainless steel or agate tank, wherein the ball-to-material ratio (the weight ratio of grinding balls to K, zr and Te materials) is 15:1;
step 2: sealing the ball milling tank, opening an exhaust valve, vacuumizing the ball milling tank, introducing argon to form protective gas to prevent oxidation, carrying out ball milling on a planetary ball mill under the argon atmosphere, wherein the process conditions for carrying out ball milling are that the rotating speed is set to be 500 revolutions per minute, carrying out ball milling for 8 hours clockwise at room temperature, and then carrying out ball milling for 8 hours anticlockwise, wherein the rotating speed of the ball mill is very high, the ball milling is stopped for half an hour for cooling every half an hour, and the ball milling is carried out for 16 hours in total;
and 3, step 3: putting the powder sample obtained in the step (3) into a grinding tool, pressing the powder into a cylindrical slice with the height of 3mm and the diameter of 10mm under the pressure of 300MPa, and keeping the sample powder in the pressing tool for 8 minutes under the pressure of 300MPa in the pressing process to prevent the sample after pressing from being broken or falling off due to air holes;
and 4, step 4: placing the tabletted sample in a tube annealing furnace for heat preservation, vacuumizing a quartz vacuum tube by using a molecular pump until the vacuum degree is less than 1 multiplied by 10 -6 Pa, then filling argon for protection, setting the temperature of the tubular annealing furnace to be 550 ℃, the heating rate to be 2 ℃/min, and carrying out heat preservation sintering on the sample at the temperature of 550 ℃ for 42 hours;
and 5, step 5: and (3) putting the tabletting KCrTe sample obtained in the step (4) back into the ball milling tank, and simultaneously, according to the step (1): 2:2 stainless steel balls or agate balls with the quantity ratio of 5mm, 8mm and 12mm, repeating the ball milling process in the step 2, then tabletting the KCrTe powder sample obtained by re-grinding in the step 3, then placing the sample in a tubular annealing furnace again, repeating the annealing sintering process in the step 4, repeating the processes for 4 times, basically forming the required phase structure by the KCrSe powder subjected to heat preservation sintering in the steps 2-5, but the uniformity is poor, so that the material phase is more uniform by performing ball milling and sintering for 4 times, finally taking out the sample, putting the sample into liquid nitrogen (77K) for quenching for 20 seconds, and cooling to obtain the pure KCrSe polycrystal sample.
In this way, a KCrTe polycrystalline material was produced, the lattice structure of which is shown in fig. 2 (c) (Z = Te). FIG. 5 is a diagram showing the band structure of a polycrystalline material of KCrSe obtained in the present example, and KCrTe is a spin zero-gap semiconductor material having a zero-gap protected by lattice symmetry, as with KCrS obtained in example 1.
Example 9
Preparation d 0 -a KCrTe spin zero-energy gap semiconductor material with a d-type half-Heusler structure. The specific process comprises the following steps:
the KCrTe alloy polycrystalline material is prepared by adopting a ball milling method.
Step 1: according to a mol ratio of 1:1:1, weighing 40g of K powder, cr powder and Te powder with the purity of 99.999 percent, mixing the K powder, the Cr powder and the Te powder in a sealed agate ball-milling tank, wherein the diameter of the ball-milling tank is 80mm, and simultaneously, mixing stainless steel balls or agate balls with the diameters of 5mm, 8mm and 12mm according to the weight ratio of 1:2:2, placing the mixture into a stainless steel or agate tank, wherein the ball-to-material ratio (the weight ratio of grinding balls to K, zr and Te materials) is 15:1;
step 2: sealing the ball milling tank, opening an exhaust valve, vacuumizing the ball milling tank, introducing argon to form protective gas to prevent oxidation, carrying out ball milling on a planetary ball mill under the argon atmosphere, wherein the process conditions for carrying out ball milling are that the rotating speed is set to be 500 revolutions per minute, carrying out ball milling for 9 hours clockwise at room temperature, and then carrying out ball milling for 9 hours anticlockwise, wherein the rotating speed of the ball mill is very high, the ball milling is stopped for half an hour for cooling every half an hour, and the total grinding time is 18 hours;
and 3, step 3: putting the powder sample obtained in the step 3 into a grinding tool, pressing the powder into a cylindrical slice with the height of 3mm and the diameter of 10mm under the pressure of 350MPa, and keeping the sample powder in the pressing tool for 5 minutes under the pressure of 350MPa in the pressing process to prevent the sample after pressing from being broken or falling due to air holes;
and 4, step 4: placing the tabletted sample in a tubular annealing furnace for heat preservation, vacuumizing a quartz vacuum tube by using a molecular pump until the vacuum degree is less than 1 multiplied by 10 -6 Pa, then filling argon for protection, setting the temperature of the tubular annealing furnace at 500 ℃, the heating rate at 2 ℃/min, and carrying out heat preservation sintering on the sample at 600 ℃ for 36 hours;
and 5, step 5: and (3) putting the tabletting KCrTe sample obtained in the step (4) back into the ball milling tank, and simultaneously, according to the step (1): 2:2 stainless steel balls or agate balls with the quantity ratio of 5mm, 8mm and 12mm, repeating the ball milling process in the step 2, then tabletting the KCrTe powder sample obtained by re-grinding in the step 3, then placing the sample in a tubular annealing furnace again, repeating the annealing sintering process in the step 4, repeating the processes for 3 times, basically forming the required phase structure by the KCrTe powder subjected to heat preservation sintering in the steps 2-5, but the uniformity is poor, so that the material phase is more uniform by performing ball milling and sintering for 3 times, finally taking out the sample, putting the sample into liquid nitrogen (77K) for quenching for 15 seconds, and cooling to obtain the pure KCrTe polycrystal sample.
In this way, a KCrTe polycrystalline material was produced, the lattice structure of which is shown in fig. 2 (c) (Z = Te). FIG. 5 is a diagram showing the band structure of a KCrTie polycrystalline material produced in this example, and KCrTe is also a spin zero-gap semiconductor material having a zero-gap protected by lattice symmetry, as is the case with KCrS produced in example 1.
While the invention has been described with reference to preferred embodiments, it will be apparent to those skilled in the art that the technology can be practiced with modification, or with appropriate modification and combination, of the specific embodiments described herein without departing from the spirit and scope of the invention. It is expressly intended that all such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and content of the invention.
Claims (6)
1. Has lattice symmetryA method for preparing a spin zero-energy-gap semiconductor material with a sexual protection zero-energy gap; structure is d 0 -KCrZ alloy of the d-type half-Heusler; wherein Z = S, se or Te; the semiconductor material has a spin polarizability of 100% and a spin polarizability of 5 mu B The integer molecular magnetic moment of (a); the preparation method comprises the following steps:
1) Mixing K powder, cr powder and Z powder according to a molar ratio of 1:1:1, mixing the mixture in a sealed stainless steel or agate ball-milling tank, and simultaneously selecting large, medium and small stainless steel balls or agate balls with different specifications and diameters of 5-12 mm according to a ratio of 1:2:2, placing the mixture into a stainless steel or agate tank, wherein the ball-material ratio is 8-20: 1;
2) Vacuumizing a ball milling tank at room temperature, performing ball milling on a planetary ball mill in an argon atmosphere, wherein the rotating speed of the ball mill is 500-700 r/min, the ball milling time is 8-20 hours in total, and stopping the ball milling for half an hour and cooling the ball milling for half an hour within the ball milling period of 8-20 hours; the ball milling time is 8-20 hours, wherein clockwise milling is carried out for 4-10 hours, and anticlockwise milling is carried out for 4-10 hours;
3) Placing the ball-milled powder sample in a grinding tool, keeping the pressure of the grinding tool at 250-350 MPa for 5-10 minutes, and finally pressing the powder sample into a sheet shape;
4) Placing the pressed sample in a tubular annealing furnace, vacuumizing a quartz vacuum tube by using a molecular pump, and then filling argon for protection, wherein the annealing heat preservation temperature is set to be 380-600 ℃, and the heat preservation sintering time is 36-48 hours;
5) And (4) putting the pressed KCrZ sample obtained in the step (3) back into the ball milling tank again, putting the grinding balls into the ball milling tank according to the ball-to-material ratio in the step (1) and the quantity ratio of the grinding balls with different specifications, repeating the ball milling process in the step (2), then pressing the KCrZ powder sample obtained by re-grinding according to the step (3), putting the pressed KCrZ powder sample into a tubular annealing furnace, repeating the annealing and sintering process in the step (4), repeating the processes for 3-5 times, finally taking out the sample, putting the sample into liquid nitrogen for quenching, and cooling to obtain the pure KCrZ polycrystal sample.
2. The method according to claim 1, wherein the purity of K powder, cr powder and Z powder is 99.99% or more.
3. The method of claim 1, wherein the ball to feed ratio is 15:1.
4. the method as set forth in claim 1, wherein the ball milling time for KCrS in the step 2) is 12 to 16 hours, wherein the ball milling is performed for 6 to 8 hours clockwise and then for 6 to 8 hours counterclockwise; for KCrSe, the ball milling time is 10-14 hours, wherein the ball milling is carried out for 5-7 hours clockwise, and then the ball milling is carried out for 5-7 hours anticlockwise; the ball milling time of the KCrTe is 14 to 18 hours, wherein the ball milling is carried out for 7 to 9 hours in a clockwise way, and then the ball milling is carried out for 7 to 9 hours in a counterclockwise way.
5. The method of claim 1, wherein the annealing temperature of step 3) for KCrS is set to 400-500 ℃; for KCrSe, the annealing heat preservation temperature is set to be 380-450 ℃; for KCrTe, the annealing temperature is set to be 500-600 ℃.
6. The method according to claim 1, wherein the quenching in step 4) is performed in 77K liquid nitrogen for 15 to 25 seconds.
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