Bismuth telluride
Introduction
Bismuth telluride (Bi2Te3) is a gray powder that is a compound of bismuth and tellurium. It is a narrow-gap layered semiconductor with a trigonal unit cell. The high thermoelectric efficiency of bismuth telluride has led to its widespread use in power generation and refrigeration applications.
Structure and Properties
Bismuth telluride crystallizes in a hexagonal system with the space group R3m. The structure consists of quintuple layers of atoms (Te-Bi-Te-Bi-Te) that are weakly bonded together by van der Waals forces. This layered structure results in highly anisotropic properties, with the electrical and thermal conductivities being much greater parallel to the layers than perpendicular to them.
Synthesis
Bismuth telluride can be synthesized by a variety of methods, including Bridgman–Stockbarger, zone melting, and chemical vapor deposition (CVD). These methods allow for the control of the stoichiometry and crystallinity of the material, which are critical for its thermoelectric performance.
Applications
Due to its high thermoelectric efficiency, bismuth telluride is most commonly used in thermoelectric cooling and power generation devices. It is also used in topological insulators, which are materials that conduct electricity on their surface, but not in their bulk.