Crystal structure and Uses of Bismuth telluride

Bismuth telluride (Bi2Te3) is a gray powder, it is a semiconductor, which, when alloyed with antimony or selenium, is an efficient thermoelectric material for refrigeration or portable power generation.

Crystal structure

The crystal structure of Bismuth telluride is a rhombohedral tetradymite-type with the space group R-3m, and is described by a hexagonal unit cell, as shown in Fig. 1. The unit cell is composed of five covalently bonded monatomic sheets along the c-axis in the sequence –Te(1)–Bi–Te(2)–Bi–Te(1)–Te(1)–Bi–Te(2)–Bi–Te(1)–.

Figure 1.Schematic crystal structure of Bi2Te3

Properties as a thermoelectric material

Bismuth telluride is a narrow-gap layered semiconductor with a trigonal unit cell. The valence and conduction band structure can be described as a many-ellipsoidal model with 6 constant-energy ellipsoids that are centered on the reflection planes.Bi2Te3 cleaves easily along the trigonal axis due to Van der Waals bonding between neighboring tellurium atoms. Due to this, bismuth-telluride-based materials used for power generation or cooling applications must be polycrystalline. Furthermore, the Seebeck coefficient of bulk Bi2Te3 becomes compensated around room temperature, forcing the materials used in power-generation devices to be an alloy of bismuth, antimony, tellurium, and selenium.

Uses

Bismuth Telluride is a narrow gap-layered semiconductor with high thermal conductivity. Recent research has confirmed that bismuth telluride may significantly increase the speed of microchips and be the basis for the emerging next-generation technology known as "Spintronics".

Preparation

Bismuth telluride may be prepared simply by sealing mixed powders of bismuth and tellurium metal in a quartz tube under vacuum (critical, as an unsealed or leaking sample may explode in a furnace) and heating it to 800℃ in a muffle furnace.