CN101220513B

CN101220513B - Thermal treatment method for improving type N polycrystal Bi2Te3thermoelectricity capability

Info

Publication number: CN101220513B
Application number: CN2007101753041A
Authority: CN
Inventors: 张波萍; 赵立东; 李敬锋; 刘玮书
Original assignee: University of Science and Technology Beijing USTB
Current assignee: University of Science and Technology Beijing USTB
Priority date: 2007-09-28
Filing date: 2007-09-28
Publication date: 2010-12-08
Anticipated expiration: 2027-09-28
Also published as: CN101220513A

Abstract

A heat treatment method that increases the thermoelectric property of N-type polycrystal Bi2Te3 belongs to the technical field of energy materials. The method is divided into two parts: preparing of an N-type polycrystal Bi2Te3 thermoelectric material and annealing. At first, high purity Bi and Te are synthetized into Bi2Te3 compound powder by mechanical alloying, and an N-type polycrystal Bi2Te3block material is prepared by spark plasma sintering, and then the Bi2Te3 block material is treated with vacuum annealing. Through the annealing treatment, the method increases the thermoelectric property of the N-type polycrystal Bi2Te3 and has the advantages of simple process, low cost and strong practicability, etc.

Description

A kind of raising N type polycrystalline Bi 2Te 3The heat treating method of thermoelectricity capability

Technical field

The invention belongs to the energy and material technical field, a kind of raising N type polycrystalline Bi particularly is provided ₂Te ₃The heat treating method of thermoelectricity capability relates to mechanical alloying (MA), discharge plasma sintering (SPS) and annealing treating process.

Background technology

Bi ₂Te ₃The base alloy is the best thermoelectric material of performance under the current room temperature, also be to study the earliest one of the most sophisticated thermoelectric material, have bigger Seebeck coefficient and lower thermal conductivity, zero dimension thermoelectric figure of merit ZT is about 1 under the room temperature, and great majority refrigeration and low temperature temperature difference converting electrical energy element all are to adopt this class material at present.Bi ₂Te ₃Crystal has rhombus six sides' synusia shape structure, and each structure cell is made up of three parts, and each part along the axial atomic arrangement of c is-Te ⁽¹⁾-Bi-Te ⁽²⁾-Bi-Te ⁽¹⁾-, Te ⁽¹⁾Between-Bi covalent linkage and ionic linkage combination, Te ⁽²⁾Between-Bi covalent bonds, the Te between each part ⁽¹⁾-Te ⁽¹⁾Be the Van der Waals force combination, this kind crystalline structure makes material show as anisotropy on macro property.Usually adopt zone melting [D.-B.Hyun, T.S.Oh, J.S.Hwang, J.D.Shim, N.V.Kolomoets, Scripta Mater.40 (1998) 49.], Bridgman[O.Yamashita, S.Tomiyoshi, K.Makita, J.Appl.Phys.93 (2003) 368.] and Czochralsky method [O.B.Sokolov, S.Y, Skipidarov, N.I.Duvankov, J.Cryst.Growth 236 (2002) 181.] oriented growth or the monocrystal material of preparation has very high thermoelectricity capability, but because thick crystal grain and Te ⁽¹⁾-Te ⁽¹⁾Between Van der Waals force make that the mechanical property of monocrystal material is very poor.In order to improve the mechanical property of material, generally adopt powder metallurgy and agglomerating method to prepare polycrystalline material [X.A.Fan, J.Y.Yang, W.Zhu, H.S.Yun, R.G.Chen, S.Q.Bao, X.K.Duan, J.Alloys Compd.420 (2006), 256.; L.D.Chen, Materials Integration 18 (2005) 18.].But the thermoelectricity capability of polycrystalline material is but far below oriented growth or monocrystal material, all multifactor [the T.S.Oh such as lattice imperfection that specific conductivity descends, the mechanical deformation in powder metallurgy process causes that cause by crystal boundary that comprise of restriction polycrystalline material thermoelectricity capability, D.-B.Hyun, N.V.Kolomoets, Scripta Mater., 2000,42 (9): 849.; D.-B.Hyun, T.S.Oh, J.S.Hwang, J.D.Shim, N.V.Kolomoets, Scripta Mater., 1998,40 (1): 49.].Schultz etc. find P type Bi ₂Te ₃Monocrystalline becomes N-type semiconductor through behind the compressional deformation, mainly is because produced a large amount of alms giver's lattice imperfections in deformation process, has influenced carrier concentration, and N type current carrier is provided.[I.Weinberg，C.W.Schultz，J.Phys.Chem.Solids，1966，27(2)：474.]。Navr á til etc. has reported P type Sb _1.5Bi _0.5Te ₃Thereby block materials has reduced carrier concentration [T. through having produced alms giver's lattice imperfection after the milled processed J.Navr á til, J.Hor á k, D.Bachan, A. Solid State Ionics, 2007,117 (39-40): 3513.].The resistivity of thermoelectric material (ρ) is relevant with carrier concentration (n) with Seebeck coefficient (α), good electrical transmission performance (power factor, α ²/ ρ) can obtain [T.Thonhauser, G.S.Jeon, G.D.Mahan, J.O.Sofo, Phys.Rev.B, 2003,68:205207.] by optimizing carrier concentration.We adopt MA and SPS to prepare N type Bi in earlier stage ₂Te ₃Block materials [L.D.Zhao, B.P.Zhang, J.-F.Li, M.Zhou, W.S.Liu, Physica B:CondensedMatter, 2007, in press; L.D.Zhao, B.P.Zhang, J.-F.Li, M.Zhou, W.S.Liu, J.Liu, J. Alloys Compd., 2007, in press.].MA synthesizes Bi ₂Te ₃Powdered alloy is the process of a high-energy ball milling, cold welding, bump, pulverizing, influences carrier concentration since mechanical deformation and process of lapping can produce lattice imperfection, and we can infer in the MA process and also can produce a large amount of lattice imperfections so.Therefore, be necessary to study the Bi of lattice imperfection to MA and SPS preparation ₂Te ₃Effect of material performance yet there are no the pertinent literature report.The present invention passes through Bi ₂Te ₃Block materials carries out anneal, has reduced the lattice imperfection in the material, has further optimized carrier concentration, has improved Bi ₂Te ₃Thermoelectricity capability, confirmed Bi simultaneously ₂Te ₃The stability of block materials after long term annealing is handled, this is to Bi ₂Te ₃Application on thermo-electric device has far reaching significance.

Summary of the invention

The object of the present invention is to provide a kind of raising N type polycrystalline Bi ₂Te ₃The heat treating method of thermoelectricity capability has been realized synthetic and preparation time is short, technology is simple.

The present invention adopts MA and SPS to prepare polycrystalline Bi ₂Te ₃Thermoelectric material carries out anneal again.Main purpose is to improve the thermoelectricity capability of material by the design annealing treating process.Concrete technical process:

1, with the Bi of high-purity (99.999%), Te simple substance as initial feed, press Bi: Te=2: 3 atomic ratios batching.

2, raw material is put into ball grinder, in order to prevent powder oxidation in the MA process, feed rare gas element and dry grind, rotating speed is 100～500rpm, and the time is 15min～96h.

3, dry grinding back adds dehydrated alcohol as the medium wet-milling, when inlet mouth feeds argon gas, injects ethanol in the air outlet with needle tubing, has injected to close the air outlet earlier behind the ethanol and close inlet mouth again.The wet-milling rotating speed is 50～300rpm, and the time is 15min～12h, mainly is to prevent powder agglomates, makes its ball milling more even.

4, the powder of alloying oven dry obtains dry powder.Bake out temperature is 20～200 ℃, and the time is 4～20h.

5, the Bi after will synthesizing ₂Te ₃The material powder is packed in the graphite jig of Φ 10～20mm, puts sintering in the discharge plasma sintering stove into, and the vacuum tightness of sintering environment is 4～7Pa.Carry out sintering under certain temperature, pressure, soaking time, sintering temperature is 200～500 ℃, and soaking time is 2～8min, and sintering pressure is 20～60MPa, and heat-up rate is 40～180 ℃/min.Obtaining Φ 10～20mm at last, highly is the Bi of 4～6mm ₂Te ₃Block materials.

6, after the block materials that (5) step sintering is obtained carries out the surface finish processing, in the Glass tubing of packing into, then Glass tubing is vacuumized, the pressure in pipe is less than 10 ^-3Behind the Pa, carry out encapsulation process.The Glass tubing that to seal sample is then put into box-type furnace and is carried out anneal, is heated by room temperature, is heated to 100～400 ℃, is incubated furnace cooling after 1～150 hour.Fig. 1 represents the X-ray diffractogram through differing temps annealing block sample after 10 hours, as can be seen from the figure is Bi through the main X-ray diffraction peak of all block materials after the differing temps anneal ₂Te ₃Characteristic peak.After the anneal temperature was brought up to 523K by 423K, the oxide compound Bi of Bi had appearred ₂O _2.33Along with annealing temperature further is elevated to 593K, in block materials, not only there is oxide compound Bi ₂O _2.33Phase, and Bi has appearred ₂O ₃Oxide compound.Oxide compound increases along with the rising of annealing temperature, and this may be because Te is the easy volatile element, when higher temperature (523 and 593K) down during annealing the volatilization of Te make remaining Bi element and the oxygen that powder surface adsorbs that reaction take place.And when lower temperature (423K) is annealed down, do not have the volatilization of Te, so do not form oxide compound.Fig. 2 is the fracture stereoscan photograph through differing temps annealing block sample after 10 hours.We observe after annealing under the 423K temperature from figure, because growing up of crystal grain makes sample become fine and close.Along with the rising of annealing temperature, Bi ₂Te ₃The grain-size of block increases to some extent, but has occurred some pores that caused by the volatilization of Te simultaneously.

With the sample before and after the anneal, carry out test resistance rate (ρ) after the surface finish, Seebeck coefficient (α) and thermal conductivity parameters such as (κ) with sand paper.With power factor P.E.=α ²The electric property of/ρ evaluating material, zero dimension thermoelectric figure of merit ZT=(α ²/ ρ κ) thermoelectricity capability of T evaluating material.Fig. 3 has compared the electric property through differing temps anneal block sample after 10 hours.Compare with the sample of unannealed processing, the Seebeck coefficient of material is along with the rising of annealing temperature obviously increases (Fig. 3 (a)); The resistivity of material reduces after through 423 K anneal, along with the rising of annealing temperature further increases (Fig. 3 (b)); Power factor is by the 2.10mW/mK of unannealed processing sample ²Bring up to the 2.35mW/mK after 423K anneals ²(Fig. 3 (c)).Thermal conductivity through material after the 423 K anneal increases, along with the further raising of annealing temperature, the density of sample descends, and makes thermal conductivity reduce (Fig. 4), the ZT value 0.94 is brought up to 1.01 after the 423K anneal before the anneal, has improved about 7.4% (Fig. 5).

The invention has the advantages that: compared with prior art, polycrystalline Bi ₂Te ₃Synthetic and the preparation time of material is short; Annealing process is simple, and is practical; Under lower cost, can improve the thermoelectricity capability of material.

Description of drawings:

Fig. 1 represents through the Bi of differing temps annealing after 10 hours ₂Te ₃The X-ray diffractogram of block materials.

Fig. 2 represents through the Bi of differing temps annealing after 10 hours ₂Te ₃The fracture apperance of block materials.

Fig. 3 represents through the Bi of differing temps annealing after 10 hours ₂Te ₃Block materials is Seebeck coefficient (a) under 423K, resistivity (b) and power factor (c).

Fig. 4 represents through the Bi of differing temps annealing after 10 hours ₂Te ₃The thermal conductivity of block materials under 423K.

Fig. 5 represents through the Bi of differing temps annealing after 10 hours ₂Te ₃The ZT value of block materials under 423K.

Embodiment:

At first use mechanical alloying method (MA) preparation Bi ₂Te ₃Forerunner's fines; this method is according to 2: 3 atomic ratio proportionings with high-purity Bi and Te simple substance powder; put into planetary high-energy ball mill together and carry out mechanical alloying under protection of inert gas, carry out wet-milling again behind the dry grinding synthetic compound, oven dry at last obtains Bi ₂Te ₃The base fines; With discharge plasma sintering (SPS) with Bi ₂Te ₃Powdered preparation becomes block materials, and sintering temperature is 200～500 ℃, and soaking time is 2～8min, and pressure is 20～60MPa; The block materials that sintering is obtained carries out in the Glass tubing of packing into, then Glass tubing being vacuumized after surface finish handles, and the pressure in pipe is less than 10 ^-3Behind the Pa, carry out encapsulation process.The Glass tubing of sealing sample is put into box-type furnace carry out anneal, heat, be heated to 100～400 ℃, be incubated furnace cooling after 1～150 hour by room temperature.

Table 1 has provided several preferred embodiments of the present invention:

In sum, the present invention is by the polycrystalline Bi to MA and SPS preparation ₂Te ₃Thermoelectric material carries out anneal, has improved the thermoelectricity capability of material.

Claims

1. one kind is improved N type polycrystalline Bi ₂Te ₃The heat treating method of thermoelectricity capability is characterized in that technology is:

(1) Bi, Te simple substance that adopts purity 99.999% be as initial feed, and by Bi: Te=2: mixed powder is prepared burden, is mixed into to 3 atomic ratios;

(2) mixed powder is put into ball grinder, in order to prevent raw material powder oxidation in ma process, feed rare gas element and dry grind, rotating speed is 100～500rpm, and the time is 15min～96h; Dry grinding back adds ethanol as the medium wet-milling, when inlet mouth feeds argon gas, injects ethanol in the air outlet with needle tubing, has injected to close the air outlet earlier behind the ethanol and close inlet mouth again; The wet-milling rotating speed is 50～300rpm, and the time is 15min～12h, prevents powder agglomates, makes its ball milling more even; The powder oven dry of alloying is obtained Bi ₂Te ₃Powder, bake out temperature are 20～200 ℃, and the time is 4～20h;

(3) with the Bi of drying ₂Te ₃Powder is packed in the graphite jig of Φ 10～20mm, puts sintering in the discharge plasma sintering stove into, and the vacuum tightness of sintering environment is 4～7Pa; Sintering temperature is 200～500 ℃, and soaking time is 2～8min, and sintering pressure is 20～60MPa, and heat-up rate is 40～180 ℃/min;

(4) after the block materials that (3) step sintering is obtained carries out the surface finish processing, in the Glass tubing of packing into, then Glass tubing is vacuumized, the pressure in pipe is less than 10 ^-3Behind the Pa, carry out encapsulation process; The Glass tubing of sealing sample is put into box-type furnace carry out anneal, be heated to 100～400 ℃, be incubated furnace cooling after 1～150 hour, obtain Bi ₂Te ₃Block materials.