Structural changes in Bi$_{2}$Te$_{3}$ under pressure.

Bi$_{2}$Te$_{3}$ based compounds continue to receive intense research activities due to the enhanced figure of merit observed in the super lattice structure with Sb$_{2}$Te$_{3}$ [1]. Synthesis of different chemical compositions with varying particle sizes and doping has gained importance subsequently. The thermo electric properties of the new compositions strongly depend on the structure and P-T phase diagram of the parent compound Bi$_{2}$Te$_{3}$. In order to understand the structural properties of Bi$_{2}$Te$_{3}$ in detail, we have performed pressure studies up to 30GPa using insitu angle dispersive and energy dispersive x-ray diffraction techniques using a diamond anvil cell with different pressure media. Bi$_{2}$Te$_{3}$ is found to undergo pressure induced structural transition around 7.8 GPa to a new high pressure phase from the ambient rhombohedral phase. This transition is found to be completely reversible with a large hysteresis observed during downloading. The details of the high pressure phase and the pressure medium dependence of the transition will be discussed further. [1]. Venkatasubramanian etal., Nature, \textbf{413}, 597 (2001)