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Single Crystal Bismuth Telluride

1956; IOP Publishing; Volume: 69; Issue: 6 Linguagem: Inglês

10.1088/0370-1301/69/6/302

1747-3837

L Ainsworth,

Advanced Chemical Physics Studies

Bismuth telluride has been investigated because of its promise as a material for thermo-electric applications. Attempts have been made to grow single crystals of the material by the Stockbarger method, by directional freezing in a horizontal boat, and by pulling from the melt. The first two methods were not found to be satisfactory because of segregation of tellurium towards the last end of the ingot to freeze. This was particularly marked at the slow speeds of withdrawal desirable for good single crystal growth. At fast speeds of withdrawal the segregation was prevented, but at these speeds large single crystals were not produced. Larger crystals, about 1 cm × 2 cm × 3 cm were produced by the pulling method, using a hydrogen atmosphere. These were all p-type of thermo-electric power 200-215μV deg-1 even when considerable departures from the stoichiometric composition Bi2Te3 were made in the charge from which the crystals were pulled. The energy gap of this material, measured optically, was 0.15 eV. A p-type single crystal specimen of thermo-electric power 200μV deg-1 had a room temperature electrical conductivity of 500 Ω-1 cm-1 parallel to the cleavage planes. The room temperature thermal conductivity of the same specimen was 0.0175 W cm-1 deg-1 parallel to the cleavage planes, and 0.0076 W cm-1 deg-1 perpendicular to the cleavage planes.