Crystal Structure of Bismuth telluride

Bismuth telluride, bismuth selenide, and all intermediate alloys Bi2Te3−xSex have the tetradymite crystal structure in the symmetry group R3¯m. The material is comprised of repeating quintuple layers of X(1)–Bi–X(2)–Bi–X(1), where the number in parentheses designates two inequivalent chalcogens (X) sites. Chalcogen atoms octahedrally coordinate bismuth atoms, and Bi octahedrally coordinates the X(2) site atoms. The X(1) site atoms are covalently bonded with three Bi atoms and by weaker van der Waals bonds with three other X(1) atoms. The Bi-X(1) bond length is close to the expected covalent bond length, while the Bi-X(2) bond is longer and near the value expected for ionic bonding. The X(2) site is preferentially occupied by Se. This site selectivity has been attributed to a reduction in bond angle strain and to the more electronegative Se occupying the site with the highest cation coordination. This is a key difference from the p-type Bi2Te3-Sb2Te3 alloy system, where Bi and Sb occupy equivalent sites without preference. The difference in bonding at each chalcogen site and the occupancy preference has significant consequences for the electrical and thermal properties of the system. The preference results in the formation of an ordered compound at Bi2Te2Se, which acts as a demarcation point between which the chalcogen site changes during alloying. If you are looking for high quality, high purity, and cost-effective Bismuth Telluride, or if you require the latest price of Bismuth Telluride, please feel free to email contact mis-asia.