CN111908482A - Multi-element rare earth boride Sm1-2xEuxBaxB6 polycrystal and preparation method and application thereof - Google Patents

Abstract

The invention discloses a multi-element rare earth boride Sm_{1‑ 2x}Eu_xBa_xB₆Polycrystalline body, preparation method and application thereof. The preparation method comprises the following steps: by Sm₂O₃、Eu₂O₃、BaCO₃、B₄Mixing the C powder and the B powder serving as raw materials in proportion; sm is prepared by adopting a boron/carbon thermal reduction method_1‑2xEu_xBa_xB₆A single phase powder; the powder is put into a graphite die, and hot-pressed and sintered by adopting a sectional type heating-heat preservation-sectional type cooling mode and a linear pressurization-then linear depressurization mode to prepare Sm_1‑2xEu_xBa_xB₆The polycrystal, wherein x is more than or equal to 0.1 and less than or equal to 0.3. The polycrystal prepared by the invention is single-phase, high in purity, high in density and excellent in emission performance, and can be used as a cathode material; the preparation method has the advantages of simple preparation process, small pressing pressure and low production cost, and can prepare the polycrystal with different sizes.

Description

Multicomponent rare earth boride Sm1-2xEuxBaxB6Polycrystalline body, preparation method and application thereof

Technical Field

The invention relates to the technical field of rare earth boride cathode materials, in particular to a multi-element rare earth boride Sm_1-2xEu_xBa_xB₆Polycrystalline body, preparation method and application thereof.

Background

From LaB₆Since the advent, rare earth hexaboride (REB)₆) Because of its unique structure and performance, it can replace traditional tungsten cathode and be widely used in radar, plasma engine and ion thruster, high power emission tube, magnetron, electron source of electron beam and ion beam, electric light source device, vacuum micro/nano electronic device and electronic emitter, etc. Rare earth hexaboride is used as a key cathode material for thermionic emission, and has high melting point, high hardness, good thermal stability, stable chemical properties, high conductivity, low electron work function (work function), ion bombardment resistance and the like, which are widely concerned by researchers. As REB₆One, SmB₆The insulator is a small band gap insulator formed by hybridization of a narrow f energy band and a wide conduction band, has rich surface electronic states and strong correlation effect of f-layer electrons, and can be used as an excellent cathode material. SmB at atmospheric pressure₆In mixed valence state 2.7(4 f)⁶And 4f⁵5d configuration ratio of about 3:7), 4f at near fermi level&The 4d electronic structure is in a large density of states, and through continuous research, the inventor realizes that SmB is doped by alkali/rare earth elements₆The valence state and the electron density at the diluted near-Fermi level can be adjusted, and the electron emission characteristic is improved; meanwhile, heterogeneous metal element doping can change the atom density, atom arrangement and chemical composition of the near-surface emission surface, and influence the electron distribution state of the emission surface.

At present, the rare earth hexaboride polycrystal is mainly prepared by a pressureless sintering method, a hot pressing sintering method, a discharge plasma sintering method and the like, wherein the pressureless sintering method has simple process and high economic value, but the prepared polycrystal is hard and crisp and has low density; the discharge plasma sintering method has the advantages of rapid temperature rise, uniform heating, high efficiency and the like, but the method has high equipment requirement, large technical difficulty, small product yield and difficult industrial realization; the hot-pressing sintering method is a main method for industrially preparing polycrystal, but the common hot-pressing sintering method has the problems of high pressing pressure, long time, large internal stress of the crystal, inconvenience for subsequent processing design and the like.

Chinese patent application Nos. 200810225029.4 and 200810239385.1 both disclose a multi-element rare earth boride (La)_xRE_1-x)B₆And (La)_xBa_1-x)B₆A cathode material and a preparation method thereof, and particularly discloses a method for preparing rare earth nano powder by adopting electric arc evaporation and condensation and then preparing high-purity and high-density (La) by adopting a Spark Plasma Sintering (SPS) technology_xRE_1-x)B₆(RE is any one of Ce, Pr, Nd, Sm, Eu and Gd) and (La)_xBa_1-x)B₆The preparation process of the polycrystalline block is complex, the equipment requirement is high, the technical difficulty is high, the yield is low, the raw material needs high-purity elemental rare earth metal, the cost is high, and the method is not suitable for industrial production.

Chinese applications No. 201510163304.4 and No. 201711463453.8 both disclose a multi-element rare earth boride polycrystalline cathode material and a preparation method thereof, and particularly disclose preparation of high-density multi-element rare earth boride (La) by ball milling mixing-hot pressing sintering_xCe_1-x)B₆And (La)_xSr_1-x)B₆Polycrystalline cathode method, but ball-milled mixed (La) in the above preparation method_xCe_1-x)B₆Impurities generated by ball milling abrasion are inevitably introduced into the powder raw material, and La is also included₂O₃Mixing SrO and B powder, ball milling, and hot pressing sintering to obtain (La)_xSr_1-x)B₆Polycrystalline bodies containing residues of insufficient reactionLa₂O₃SrO or B, and other impurities that reduce the purity of polycrystalline cathodes, cause scattering of electrons, and also cause cathode poisoning, affecting the conductivity, emission characteristics, and lifetime of the cathode.

Disclosure of Invention

Based on the technical scheme, the invention aims to overcome the application limit of binary rare earth boride in the field of thermionic emission, simplify and optimize the preparation method of the multi-element rare earth boride, reduce the technical difficulty, the production cost and the energy consumption, and provide the multi-element rare earth boride Sm_1-2xEu_xBa_xB₆Polycrystalline body, preparation method and application thereof.

The invention relates to a method for preparing binary rare earth boride SmB by alkali/rare earth elements₆Doping to enhance SmB₆The state density of the Fermi surface is adjusted to reduce SmB₆The work function of the cathode material is developed and used as a device in the field of cathode materials, particularly in the field of medium and low temperature cathode materials. The invention adopts a boron/carbon thermal reduction method to obtain Eu and Ba atoms to replace SmB₆Sm having some Sm atoms in the lattice_1-2xEu_xBa_xB₆After the single-phase powder is processed by an improved hot-pressing sintering forming process, the Sm is prepared_1-2xEu_xBa_xB₆The polycrystal is single-phase, has the advantages of high purity, high density and excellent emission performance, and solves the problems of high pressing pressure, complex preparation process, high cost, limited size of the prepared product and the like in the prior art.

The above purpose of the invention is realized by the following technical scheme:

according to one aspect of the invention, the invention provides a multi-element rare earth boride Sm_1-2xEu_xBa_xB₆A method for producing a polycrystalline body, comprising the steps of:

step S1, using Sm₂O₃、Eu₂O₃、BaCO₃、B₄Mixing the C powder and the B powder serving as raw materials according to a ratio;

step S2, passing boron/carbonHeat reduction method to prepare Sm_1-2xEu_xBa_xB₆A single phase powder;

step S3, mixing Sm_1-2xEu_xBa_xB₆Loading single-phase powder into a graphite die, and carrying out hot-pressing sintering by adopting a sectional heating-heat preservation-sectional cooling mode and a linear pressurization-then-linear depressurization mode to prepare Sm_1-2xEu_xBa_xB₆The polycrystal, wherein x is more than or equal to 0.1 and less than or equal to 0.3.

In the invention, the modes of sectional heating-heat preservation-sectional cooling and linear depressurization after linear pressurization are temperature-pressure double-gradient low-pressure sintering processes obtained by improving the traditional hot-pressing sintering process, and the maximum pressing pressure is only 3.5-6 MPa.

Preferably, in step S1, the raw materials are calculated and weighed according to the stoichiometric ratio in the synthetic route, wherein Sm is₂O₃、Eu₂O₃、BaCO₃Multiplying the obtained product by an excess coefficient of 1-1.5, wherein the synthetic route is as follows:

(1-2x)Sm₂O₃+xEu₂O₃+2xBaCO₃+3B₄C+B＝2Sm_1-2xEu_xBa_xB₆+(x+4)CO↑+BO↑+(x-1)CO₂↑。

preferably, in step S1, the purity of each raw material is: sm₂O₃Purity is more than or equal to 99.9 percent, and Eu₂O₃Purity is more than or equal to 99.9 percent, and BaCO₃Analytical purity AR is more than or equal to 99%, B₄The purity of C is more than or equal to 99.9 percent, and the purity of B powder is more than or equal to 99.99 percent.

Preferably, Sm is prepared by boron/carbothermic reduction in step S2_1-2xEu_xBa_xB₆Single-phase powders, in particular comprising: placing the graphite crucible filled with the mixed materials in a vacuum carbon tube furnace, vacuumizing until the vacuum degree is lower than 0.01Pa, starting heating, heating to 1800 ℃ at the heating rate of 10 ℃/min, preserving heat for 1-2 h, cooling to room temperature along with the furnace, and taking out; taking out, grinding, acid washing, water washing, vacuum drying, grinding and screening to obtain Sm_1-2xEu_xBa_xB₆Solid solution single phase powder.

More preferably, Sm is obtained after sieving in step S2 by grinding_1-2xEu_xBa_xB₆Single-phase powder with purity not less than 99.8% and granularity D90<30μm。

Preferably, in the temperature-pressure dual-gradient low-pressure sintering process, the hot-pressing sintering is performed by adopting a sectional temperature rise-heat preservation-sectional temperature reduction mode and a linear pressure reduction mode after linear pressurization, and the process comprises the following steps:

heating to 1900 ℃ by adopting a three-stage heating mode, preserving heat for 30-40 min, then heating to 2000 ℃, and continuing preserving heat for 40-70 min; wherein the heating rate is 10-50 ℃/min in the heating process;

then, cooling by adopting a sectional cooling mode, turning off a power supply when the temperature is reduced to 1000 ℃, and naturally cooling to room temperature along with the furnace to obtain Sm_1-2xEu_xBa_xB₆A polycrystalline body;

and in the three-stage heating and temperature rising stage, when the temperature rises to 1700 ℃, pressurizing by adopting a linear pressurizing mode, wherein the pressurizing rate is 30-40 Pa/min, pressurizing to a preset pressure value, and then relieving the pressure by adopting a linear pressure reducing mode, and the pressure relieving rate is 90-110 Pa/min, wherein the preset pressure value is 3.5-6 MPa.

Preferably, the heating to 1900 ℃ by adopting a three-stage heating mode comprises the following steps: a first temperature rise stage, wherein the temperature is raised from room temperature to 700 ℃; a second temperature rise stage, wherein the temperature is raised from 700 ℃ to 1700 ℃; the third temperature raising stage is to raise the temperature from 1700 ℃ to 1900 ℃. Wherein the temperature rise rate of the first temperature rise stage is 10-15 ℃/min; the temperature rise rate of the second temperature rise stage is 40-50 ℃/min; the temperature rise rate in the third temperature rise stage is 10 ℃/min. The temperature rise rate after heat preservation is 10 ℃/min.

Preferably, the cooling by a segmented cooling method includes: a first cooling stage, wherein the temperature is reduced from 2000 ℃ to 1700 ℃; a second cooling stage, wherein the temperature is reduced from 1700 ℃ to 1000 ℃; and in the third cooling stage, cooling from 1000 ℃ to room temperature. Wherein the cooling rate of the first cooling stage is 15-25 ℃/min; the cooling rate of the second cooling stage is 30-40 ℃/min; the third cooling stage is natural cooling.

Preferably, in step S3, Sm is added_1-2xEu_xBa_xB₆Before the single-phase powder is filled into the graphite mould, the method also comprises the following steps: coating the inner wall of the mould with graphite paper, and mixing with the Sm_1-2xEu_xBa_xB₆The end face of the single-phase powder contacted with the upper surface and the lower surface is covered with graphite paper.

Preferably, in step S3, the hot press sintering is performed under the protection of Ar.

Preferably, in step S3, the obtained Sm is prepared_1-2xEu_xBa_xB₆The polycrystal has a single-phase structure, the purity is more than or equal to 99.2 percent, and the density is high>95 percent, and the resistivity is less than or equal to 270 mu omega cm.

According to another aspect of the invention, the invention provides a multi-element rare earth boride Sm_1-2xEu_xBa_xB₆A polycrystalline body. Wherein, the multi-element rare earth boride Sm_1-2xEu_xBa_xB₆The polycrystal is prepared by the above preparation method.

According to still another aspect of the invention, the invention provides a multi-element rare earth boride Sm_1-2xEu_xBa_xB₆The application of the polycrystal in cathode materials. Wherein, the multi-element rare earth boride Sm_1-2xEu_xBa_xB₆The polycrystal is prepared by the above preparation method.

Compared with the prior art, the invention has the following beneficial effects: the invention adopts boron/carbon thermal reduction method to obtain Eu and Ba atoms to replace SmB after mixing raw materials according to the proportion₆Sm having some Sm atoms in the lattice_1-2xEu_xBa_xB₆The Sm is prepared by hot-pressing and sintering single-phase powder of solid solution by adopting an improved hot-pressing sintering process, namely a temperature-pressure double-gradient low-pressure sintering process, specifically adopting a sectional heating-heat preservation-sectional cooling mode and a linear pressure reduction mode after linear pressurization_1-2xEu_xBa_xB₆The polycrystal has simple preparation process, small pressing pressure (3.5-6 MPa),Low production cost and can prepare the multi-element rare earth boride Sm with different sizes_1-2xEu_xBa_xB₆A polycrystalline body. The polycrystal has a single-phase structure after X-ray diffraction analysis, and has purity of more than or equal to 99.2 percent, high density and relative density through EDS (electron-beam diffraction) spectrum analysis>95 percent, and the resistivity is less than or equal to 270 mu omega cm. Can be used as a cathode material, in particular to the application of a device in the field of medium and low temperature cathode materials.

Drawings

FIG. 1 is a graph of a temperature-pressure dual gradient low pressure sintering process of the present invention;

FIG. 2 is Sm prepared in example 1_0.4Eu_0.3Ba_0.3B₆A physical photograph of the polycrystalline body;

FIG. 3 is Sm prepared in example 1_0.4Eu_0.3Ba_0.3B₆XRD spectrogram of the polycrystalline sample;

FIG. 4 is Sm prepared in example 2_0.6Eu_0.2Ba_0.2B₆XRD spectrogram of the polycrystalline sample;

FIG. 5 is Sm prepared in example 3_0.8Eu_0.1Ba_0.1B₆XRD spectrum of polycrystalline sample.

Detailed Description

The present invention is further described in the following with reference to the drawings and specific examples, which will assist those skilled in the art to further understand the present invention, and the detailed description and specific operation procedures are given below, but the scope of the present invention is not limited to the following examples, and the spirit and scope of the present invention is limited only by the claims.

Example 1

The invention adopts the boron/carbon thermal reduction method-hot pressing sintering integrated process to prepare the Sm with different sizes and high performance_0.4Eu_0.3Ba_0.3B₆A polycrystalline body comprising the steps of:

step 1: raw material Sm₂O₃、Eu₂O₃、BaCO₃、B₄C. And B powder is prepared from the following components in a stoichiometric ratio of 0.4:0.3:0.6:3:1 (molar ratio) in which Sm is₂O₃、Eu₂O₃、BaCO₃Multiplying the obtained product by an excess coefficient of 1-1.5, uniformly mixing the raw materials, and placing the mixture in a graphite crucible;

step 2: placing the graphite crucible in a vacuum carbon tube furnace, vacuumizing until the vacuum degree is lower than 0.01Pa, and starting heating, wherein the process parameters are as follows: heating at a rate of 10 ℃/min, keeping the temperature at 1800 ℃ for 1-2 h, cooling to room temperature along with the furnace, and taking out;

and step 3: grinding the synthetic product in the step 2, acid washing (0.5mol/L dilute hydrochloric acid), water washing, vacuum drying, and then grinding and screening (500 meshes) to obtain high-purity Sm_0.4Eu_0.3Ba_0.3B₆Single phase powder of particle size D90<30μm；

And 4, step 4: sm obtained in step 3_0.4Eu_0.3Ba_0.3B₆The single-phase powder is filled into a graphite mould (phi 35mm multiplied by 150mm), the graphite mould is placed into a vacuum hot-pressing sintering furnace, hot-pressing sintering is carried out under the protection of Ar, and the sintering technological parameters are as follows: the temperature rise rate is 10 ℃/min (less than or equal to 700 ℃, 1700-1900 ℃, 1900-2000 ℃), the temperature is 40 ℃/min (700-1700 ℃), the sintering temperature is 1700-2000 ℃, the heat preservation time a is 30min, the b is 40min, the pressing pressure is 0-3.5 MPa, the pressurization rate is 40Pa/min, pressurization is carried out to a preset pressure value, the pressure relief rate is 110Pa/min, the temperature-pressure change curve in the pressing process is shown in figure 1, the temperature is reduced by adopting a sectional temperature reduction mode after the pressing is finished, the temperature reduction rate is 15 ℃/min (2000-1700 ℃), the temperature is 30 ℃/min (1700-1000 ℃), the power supply is closed and is cooled to the room temperature along with the furnace when the temperature is reduced to_0.4Eu_0.3Ba_0.3B₆A polycrystalline body.

Prepared Sm_0.4Eu_0.3Ba_0.3B₆The polycrystalline mass is blue in color (size can be seen in fig. 2), the XRD pattern is shown in fig. 3, and it can be seen that the sample is of a single-phase structure; by EDS energy spectrum analysis, the chemical purity of the polycrystal reaches 99.2 percent, the relative density is 96.3 percent, and the resistivity is 196 mu omega cm (about 196 mu omega cm).

Example 2

This example is different from example 1 in that the stoichiometric ratio of 5 raw materials in step 1 is 0.6:0.2:0.4:3:1, and is otherwise the same as example 1.

Prepared Sm_0.6Eu_0.2Ba_0.2B₆The polycrystalline block is blue in color, an XRD (X-ray diffraction) spectrum is shown in figure 4, and a sample is in a single-phase structure; by EDS energy spectrum analysis, the chemical purity of the polycrystalline reaches 99.25 percent, the relative density is 95.2 percent, and the resistivity is 258 mu omega cm.

Example 3

This example is different from example 1 in that the stoichiometric ratio of the five raw materials in step 1 is 0.8:0.1:0.2:3:1, and is otherwise the same as example 1.

Prepared Sm_0.8Eu_0.1Ba_0.1B₆The polycrystalline block is blue in color, an XRD (X-ray diffraction) spectrum is shown in figure 5, and a sample is in a single-phase structure; by EDS (electron-dispersive spectroscopy) analysis, the chemical purity of the polycrystalline reaches 99.24%, the relative density is 96.1%, and the resistivity is 270 mu omega cm.

Example 4

This example is different from example 3 in that the graphite mold in step 4 has dimensions of phi 25mm x 100mm, and is otherwise the same as example 3.

Prepared Sm_0.8Eu_0.1Ba_0.1B₆The polycrystalline block is blue in color, an XRD (X-ray diffraction) spectrum is shown in figure 5, and a sample is in a single-phase structure; by EDS energy spectrum analysis, the chemical purity of the polycrystal reaches 99.26 percent, the relative density is 97.2 percent, and the resistivity is 265 mu omega cm.

Example 5

The difference between the embodiment and the embodiment 3 is that the dimension of the graphite mold in the step 4 is phi 45mm multiplied by 150mm, the temperature rise rate is 15 ℃/min (less than or equal to 700 ℃), the temperature rise rate is 45 ℃/min (700-1700 ℃), the temperature 10 ℃/min (1700-1900 ℃, 1900-2000 ℃), the heat preservation time is 40min, the b is 55min, the pressing pressure is 0-5 MPa, the pressurization rate is 35Pa/min, the pressure release rate is 100Pa/min, the temperature reduction rate is 20 ℃/min (2000-1700 ℃), the temperature is 35 ℃/min (1700-1000 ℃), and the other steps are the same as the embodiment 3.

Prepared Sm_0.8Eu_0.1Ba_0.1B₆The polycrystalline block is blue in color, an XRD (X-ray diffraction) spectrum is shown in figure 5, and a sample is in a single-phase structure; by EDS energy spectrum analysis, the chemical purity of the polycrystal reaches 99.21%, the relative density is 96.4%, and the resistivity is 268 mu omega cm.

Example 6

The difference between the embodiment and the embodiment 3 is that the dimension of the graphite mold in the step 4 is phi 55mm multiplied by 150mm, the temperature rise rate is 15 ℃/min (less than or equal to 700 ℃), the temperature rise rate is 50 ℃/min (700-1700 ℃), the temperature 10 ℃/min (1700-1900 ℃, 1900-2000 ℃), the heat preservation time is 40min, the b is 70min, the pressing pressure is 0-6 MPa, the pressurization rate is 30Pa/min, the pressure release rate is 90Pa/min, the temperature reduction rate is 25 ℃/min (2000-1700 ℃), the temperature is 40 ℃/min (1700-1000 ℃), and the other steps are the same as the embodiment 3.

Prepared Sm_0.8Eu_0.1Ba_0.1B₆The polycrystalline block is blue in color, an XRD (X-ray diffraction) spectrum is shown in figure 5, and a sample is in a single-phase structure; through EDS (electron-dispersive spectroscopy) analysis, the chemical purity of the polycrystalline reaches 99.22%, the relative density is 95.8%, and the resistivity is 270 mu omega cm.

Sm obtained in examples 1 to 6_1-2xEu_xBa_xB₆The size, purity, relative density and resistivity of the polycrystals are shown in table 1.

TABLE 1

As can be seen from examples 1-6, the maximum pressing pressure in the preparation method is only 3.5-6 MPa, which is far less than that in the prior art; the invention can prepare Sm with different sizes_1-2xEu_xBa_xB₆Polycrystalline, and Sm prepared_1-2xEu_xBa_xB₆The polycrystal has a single-phase structure, the purity is more than or equal to 99.2 percent, and the relative density is high>95 percent, and the resistivity is less than or equal to 270 mu omega cm; with binary rare earth boride SmB₆Compared with Sm containing multicomponent rare earth boride_1-2xEu_xBa_xB₆Metallic reinforcement, fermiThe state density of the energy surface is adjusted, the work function of the cathode material is reduced, and the cathode material can be particularly applied to the field of medium-low temperature cathode materials as a device.

Claims (10)

1. Multielement rare earth boride Sm_1-2xEu_xBa_xB₆A method for producing a polycrystalline body, comprising the steps of:

step S1, using Sm₂O₃、Eu₂O₃、BaCO₃、B₄Mixing the C powder and the B powder serving as raw materials according to a ratio;

step S2, preparing Sm through boron/carbon thermal reduction method_1-2xEu_xBa_xB₆A single phase powder;

step S3, mixing Sm_1-2xEu_xBa_xB₆Loading single-phase powder into a graphite die, and carrying out hot-pressing sintering by adopting a sectional heating-heat preservation-sectional cooling mode and a linear pressurization-then-linear depressurization mode to prepare Sm_1-2xEu_xBa_xB₆The polycrystal, wherein x is more than or equal to 0.1 and less than or equal to 0.3.

2. The method according to claim 1, wherein in step S1, the raw materials are calculated and weighed based on the stoichiometric ratio in the synthetic route:

(1-2x)Sm₂O₃+xEu₂O₃+2xBaCO₃+3B₄C+B＝2Sm_1-2xEu_xBa_xB₆+(x+4)CO↑+BO↑+(x-1)CO₂↑；

the purity of each raw material is as follows: sm₂O₃Purity is more than or equal to 99.9 percent, and Eu₂O₃Purity is more than or equal to 99.9 percent, and BaCO₃Analytical purity AR is more than or equal to 99%, B₄The purity of C is more than or equal to 99.9 percent, and the purity of B powder is more than or equal to 99.99 percent.

3. The method according to claim 1, wherein Sm is produced by boron/carbon thermal reduction in step S2_1-2xEu_xBa_xB₆Single-phase powders, in particular comprising: placing the graphite crucible filled with the mixed materials in a vacuum carbon tube furnace, vacuumizing until the vacuum degree is lower than 0.01Pa, starting heating, heating to 1800 ℃ at the heating rate of 10 ℃/min, preserving heat for 1-2 h, cooling to room temperature along with the furnace, and taking out; taking out, grinding, acid washing, water washing, vacuum drying, grinding and screening to obtain Sm_1-2xEu_xBa_xB₆A single phase powder.

4. The production method according to claim 3, wherein the Sm is_1-2xEu_xBa_xB₆Single-phase powder with purity not less than 99.8% and granularity D90<30μm。

5. The method of claim 1, wherein the step S3, the hot-pressing sintering is performed by a step-wise temperature increase-temperature maintenance-step-temperature decrease method and a linear pressure decrease method, and the step S comprises:

firstly, heating to 1900 ℃ by adopting a three-section heating mode, comprising the following steps: in the first temperature rise stage, the temperature rise rate is 10-15 ℃/min, and the temperature is raised from room temperature to 700 ℃; in the second temperature rise stage, the temperature rise rate is 40-50 ℃/min, and the temperature is raised from 700 ℃ to 1700 ℃; in the third temperature rise stage, the temperature rise rate is 10 ℃/min, and the temperature is raised from 1700 ℃ to 1900 ℃;

then preserving the heat at 1900 ℃ for 30-40 min, then heating to 2000 ℃ at the heating rate of 10 ℃/min, and preserving the heat for 40-70 min;

then cooling by adopting a sectional cooling mode, comprising the following steps: in the first cooling stage, the cooling rate is 15-25 ℃/min, and the temperature is reduced from 2000 ℃ to 1700 ℃; in the second cooling stage, the cooling rate is 30-40 ℃/min, and the temperature is reduced from 1700 ℃ to 1000 ℃; in the third cooling stage, the temperature is cooled to room temperature along with the furnace at 1000 ℃;

and when the temperature is increased to 1700 ℃, pressurizing by adopting a linear pressurizing mode, wherein the pressurizing rate is 30-40 Pa/min, pressurizing to a preset pressure value, and then relieving the pressure by adopting a linear pressure reducing mode, wherein the pressure relieving rate is 90-110 Pa/min.

6. The method according to claim 5, wherein the predetermined pressure value is 3.5 to 6 MPa.

7. The method according to claim 1, wherein in step S3, Sm is added_1-2xEu_xBa_xB₆Before the single-phase powder is filled into the graphite mould, the method also comprises the following steps: coating the inner wall of the mould with graphite paper, and mixing with the Sm_1-2xEu_xBa_xB₆Covering graphite paper on the end face of the single-phase powder contacted with the upper surface and the lower surface;

in step S3, the hot-pressing sintering molding process is performed under the protection of Ar.

8. The process according to claim 1, wherein Sm 3 is produced_1-2xEu_xBa_xB₆The polycrystal has a single-phase structure, the purity is more than or equal to 99.2 percent, and the density is high>95 percent, and the resistivity is less than or equal to 270 mu omega cm.

9. A multi-element rare earth boride Sm prepared by the preparation method of any one of claims 1 to 8_{1- 2x}Eu_xBa_xB₆A polycrystalline body.

10. A multi-element rare earth boride Sm prepared by the preparation method of any one of claims 1 to 8_{1- 2x}Eu_xBa_xB₆The polycrystalline body is used as a cathode material.

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