CN101519800A

CN101519800A - Method for growing Ba8Ga16Ge30 thermoelectric monocrystal

Info

Publication number: CN101519800A
Application number: CN200910046367A
Authority: CN
Inventors: 陈立东; 侯小伟; 周燕飞; 张文清; 王丽; 张闻斌
Original assignee: Shanghai Institute of Ceramics of CAS
Current assignee: Shanghai Institute of Ceramics of CAS
Priority date: 2009-02-19
Filing date: 2009-02-19
Publication date: 2009-09-02

Abstract

The invention relates to a method for growing a Ba8Ga16Ge30 thermoelectric monocrystal. The method comprises the following steps that: 1) preparation of Ba8Ga16Ge30 powder phase is prepared, in which, elementary substances of Ba, Ga and Ge are mixed evenly according to a stoichiometric proportion, are heated for 12 to 15 hours at 1,100 DEG C under in a vacuum state, and are slowly reduced to room temperature so as to obtain pure phase Ba8Ga16Ge30 after acid cleaning; 2) Ba8Ga16Ge30 monocrystal growth is performed growth by a melt pulling method, in which, the Ba8Ga16Ge30 powder obtained in the step 1) is placed in an Al2O3 crucible, is vacuumized and inflated repeatedly in a pulling type monocrystal furnace, and is heated to a temperature of between 1,050 and 1,100 DEG C to preserve the temperature for 1 to 3 hours; reduces the temperature is reduced to a temperature of between 950 and 980 DEG C, seeds directional crystal seeds is seeded after the temperature is balanced, and the temperature is preserved for 1 to 2 hours; the temperature is slowly reduced at speed a peed of between 1 and 5 DEG C per hour; meanwhile, the crystal rotates at a speed of between 20 and 50 revolutions per minute, and the crystal is pulled at a speed of between 1 and 6 millimeters per hour. After the crystal grows to the required dimension, the crystal is lifted from the liquid surface so as to obtain the Ba8Ga16Ge30 monocrystal. The method can obtain high- quality monocrystal, and has with quick growth speed.

Description

A kind of Ba 8Ga 16Ge 30The growth method of thermoelectric monocrystal

Technical field

The present invention relates to a kind of growth method of monocrystalline, particularly a kind of Ba ₈Ga ₁₆Ge ₃₀The growth method of thermoelectric monocrystal.

Background technology

The thermo-electric conversion effect is to utilize Seebeck effect and Peltier effect to carry out the phenomenon of heat energy and the direct conversion of electric energy energy.Thermoelectric material has advantages such as volume is little, reliability is high, running cost is low, the life-span is long, and its performance quality can be used zero dimension thermoelectric figure of merit ZT (ZT=S ²σ T/ κ) characterize, wherein S, σ, κ, T are respectively Seebeck coefficient, specific conductivity, thermal conductivity and absolute temperature.As can be seen, obtain higher conversion efficiency of thermoelectric from the ZT expression formula, material must have bigger Seebeck coefficient, higher specific conductivity and lower thermal conductivity.In general, has the thermoelectricity capability that the narrow-band semiconductor material of low thermal conductance might obtain.

I type germanium base Clathrate structured material has extremely low thermal conductivity.It belongs to isometric system, spacer Pm3n.It is open crystalline structure, has the big space of cage shape in the structure, can hold foreign atom; The reactive force that foreign atom is subjected to the chemical bond of atom on every side a little less than, can disturbance in cage, thus the scattering that increases the low frequency phonon greatly reduces thermal conductivity; And foreign atom is little to the crystalline structure influence of matrix, can keep the excellent electrical properties of original crystalline structure, is very promising thermoelectric material.Result of study shows that I type germanium base Clathrate is one of material system that meets phonon glass-electron crystal (PGEC) new ideas.It is to have thermal conductivity low as glass and the material system that conducts electricity as crystal, and is the new thermoelectric material system that is hopeful to realize in middle high-temperature section application most.

The ZT of present stage I type germanium base Clathrate material is about about 1, and high-temperature section ZT value is than a higher class material in belonging to.But the Clathrate material of preparation mostly is polycrystalline greatly now, because the fluctuation of component, the material for preparing under the different situations has different performances, and the ZT value that measures is far below theoretical value.Present stage, useful flux method grew the Clathrate crystal, but the crystal of its growth is less, can't measure its thermoelectricity capability and practical application and (consult document Crystal Growth ﹠amp; Design, Vol.6, No.8,1797,2006).Although there is the investigator to go out Ba with Czochralski grown ₈Ga ₁₆Ge ₃₀Crystal, but its crystalline component fluctuation is bigger, the performance difference at each position of crystal also very big (consulting document J.Appl.Phys.99,023708,2006).

Summary of the invention

The objective of the invention is to be to provide a kind of fast growth, obtain the melt pulling growth method of monocrystalline easily, and improved the crystalline quality.

The objective of the invention is to realize by the following method:

1) preparation Ba ₈Ga ₁₆Ge ₃₀Pure phase: Ba, Ga, Ge simple substance are mixed by stoichiometric ratio, heated 12-15 hour down at 1100 ℃ under the vacuum state, slowly drop to room temperature then, use volume proportion HCl:H ₂Promptly obtain the Ba of pure phase after the dilute hydrochloric acid pickling of O=1:1 ₈Ga ₁₆Ge ₃₀

2) use melt Czochralski grown Ba ₈Ga ₁₆Ge ₃₀Monocrystalline: the Ba that step 1) is obtained ₈Ga ₁₆Ge ₃₀Place Al ₂O ₃In the crucible, putting into the pull-type single crystal growing furnace vacuumizes logical argon gas to the furnace chamber internal pressure in applying argon gas 3-4 time back repeatedly and reaches 0.10～0.15MPa, be warming up to 1050～1100 ℃ of constant temperature 1～3 hour, reduce to 950～980 ℃ then, after treating temperature equilibrium, adopt the oriented seed of (100) direction, following seed crystal, and constant temperature 1～2 hour; Speed with 1～5 ℃/h is slowly lowered the temperature, and seed crystal rotates with 20～50 rev/mins speed simultaneously, with the speed pulling crystal of 1～6mm/h.Treat that crystal growth arrives desired size, crystal is lifted from liquid level, reduce to room temperature, promptly obtain Ba with the speed of 50 ℃～60 ℃/h ₈Ga ₁₆Ge ₃₀Monocrystalline.

Step 2) pull-type single crystal growing furnace adopts alternating-current induction graphite as heating source, and thermopair adopts W/Re5-W/Re26 (C type) thermopair.

Step 2) adopt Eurotherm818 temperature program(me) controller to carry out the steady and homothermic programcontrol unit of lifting in as crystal growing process.

The powder phase of step 1) gained that adopted the powder x-ray diffraction experiment test is found the Ba of itself and standard ₈Ga ₁₆Ge ₃₀The powdery diffractometry card is consistent.

The Ba that the present invention grew ₈Ga ₁₆Ge ₃₀Monocrystalline, through crystal structure determination, each structural parameter is consistent with the data report.

The present invention is with melt Czochralski grown Ba ₈Ga ₁₆Ge ₃₀Monocrystalline can obtain high-quality monocrystalline, and technological process is fairly simple, easy handling, fast growth.

Description of drawings

Fig. 1 is Ba ₈Ga ₁₆Ge ₃₀The crystalline structure iron.

Fig. 2 is the Ba of preparation ₈Ga ₁₆Ge ₃₀The comparison of the XRD figure of powder phase and the collection of illustrative plates of Theoretical Calculation.

Embodiment

Embodiment 1: preparation Ba ₈Ga ₁₆Ge ₃₀Powder

Raw metal Ba, Ga, Ge according to the 8:16:30 molar ratio ingredient, are vacuumized behind the plumbago crucible of packing into and enclose in the silica tube.Packaged silica tube is placed on is heated to 1100 ℃ in the retort furnace, fusion is slowly reduced to room temperature and is promptly obtained Ba after 13 hours ₈Ga ₁₆Ge ₃₀Polycrystalline bulk.Use proportioning HCl:H at last ₂The dilute hydrochloric acid pickling of O=1:1, and be ground to the powder phase.

The prepared powder phase of having utilized the X-ray powder diffraction experimental analysis is with the Ba of standard ₈Ga ₁₆Ge ₃₀The powdery diffractometry card is consistent.

Embodiment 2: Czochralski grown Ba ₈Ga ₁₆Ge ₃₀Monocrystalline

50g Ba with weighing ₈Ga ₁₆Ge ₃₀Powder stock places corundum crucible, puts into the pulling growth stove then.Be warming up to 1050 ℃ and make raw material fusing, be incubated 3 hours and make raw material and mix then fast cooling to 980 ℃.After treating temperature equilibrium, (100) direction seed crystal, and constant temperature down 2 hours is reduced to the saturation point temperature then.After the temperature equilibrium, slowly lower the temperature with the speed of 1 ℃/h, crystal begins growth, and crystal rotates with 20 rev/mins speed simultaneously, with the speed pulling crystal of 6mm/h.Treat that crystal growth arrives desired size, crystal is lifted from liquid level, reduce to room temperature, promptly obtain the Ba of Φ 12mm * 25mm with the speed of 60 ℃/h ₈Ga ₁₆Ge ₃₀Monocrystalline.

Embodiment 3:

With Ba ₈Ga ₁₆Ge ₃₀Powder stock places corundum crucible, puts into the pulling growth stove then.Be warming up to 1100 ℃ and make raw material fusing, be incubated 2 hours and make raw material and mix then fast cooling to 950 ℃.After treating temperature equilibrium, (100) direction seed crystal, and constant temperature down 1 hour is reduced to the saturation point temperature then.After the temperature equilibrium, slowly lower the temperature with the speed of 5 ℃/h, crystal rotates with 30 rev/mins speed simultaneously, with the speed pulling crystal of 4mm/h.Treat that crystal growth arrives desired size, crystal is lifted from liquid level, reduce to room temperature, promptly obtain Ba with the speed of 50 ℃/h ₈Ga ₁₆Ge ₃₀Monocrystalline.

Ba to the present invention's growth ₈Ga ₁₆Ge ₃₀Crystal 2 and 3 carries out crystal structure determination, and the data consistent of each structural parameter and data report axially carries out Ba is found in the composition analysis of embodiment 2 or 3 growths with the crystalline of electronic probe (EPMA) to embodiment 2 or 3 growths ₈Ga _xGe _46-xThe fluctuation of crystalline composition is little, and x is respectively 15.7 and 15.8, and its ZT value correspondence is respectively 1.2 (1000K) and 1.3 (1000K), has higher thermoelectricity capability.Thereby confirming melt pulling growth method provided by the invention, is guaranteed to the crystalline quality of growing, and technological process is easy to control.

Claims

1, a kind of Ba ₈Ga ₁₆Ge ₃₀The growth method of thermoelectric monocrystal comprises the steps:

1) preparation Ba ₈Ga ₁₆Ge ₃₀Powder phase: Ba, Ga, Ge simple substance are mixed by stoichiometric ratio, be contained in the plumbago crucible and vacuumize and be encapsulated in the silica tube,, slowly drop to room temperature then, can obtain the Ba of pure phase after the pickling 1100 ℃ of heating 12-15 hour down ₈Ga ₁₆Ge ₃₀

2) use melt Czochralski grown Ba ₈Ga ₁₆Ge ₃₀Monocrystalline: the pure Ba that step 1) is obtained ₈Ga ₁₆Ge ₃₀Place Al ₂O ₃In the crucible, be placed in the pull-type single crystal growing furnace, vacuumize repeatedly with applying argon gas after logical argon gas, be warming up to 1050～1100 ℃ of constant temperature again 1～3 hour, and reduced to 950～980 ℃ then, treat temperature equilibrium after, adopt＜100〉direction seed crystal, following seed crystal, and constant temperature 1～2 hour; Speed with 1～5 ℃/h is slowly lowered the temperature, and seed crystal rotates with 20～50 rev/mins speed simultaneously, with the speed pulling crystal of 1～6mm/h; Treat that crystal growth arrives desired size, be cooled to room temperature after crystal is lifted from liquid level, promptly obtain Ba ₈Ga ₁₆Ge ₃₀Monocrystalline.

2, by the described Ba of claim 1 ₈Ga ₁₆Ge ₃₀The growth method of thermoelectric monocrystal, what it is characterized in that pickling is used in the step 1) is the dilute hydrochloric acid of volume proportion as 1:1.

3, by the described Ba of claim 1 ₈Ga ₁₆Ge ₃₀The growth method of thermoelectric monocrystal is characterized in that the number of times that vacuumizes repeatedly in the pull-type single crystal growing furnace with applying argon gas is 3-4 time, and logical argon gas to furnace chamber internal pressure reaches 0.10～0.15Mpa.

4, by the described Ba of claim 1 ₈Ga ₁₆Ge ₃₀The growth method of thermoelectric monocrystal is characterized in that it is 50 ℃～60 ℃/h that crystal is lifted from the speed of lowering the temperature behind the liquid level.

5, by the described Ba of claim 1 ₈Ga ₁₆Ge ₃₀Method for monocrystal growth is characterized in that: pull-type single crystal growing furnace described step 2) adopts alternating-current induction graphite as heating source, adopts C type W/Re5-W/Re26 thermocouple temperature measurement.