We report an experimental and theoretical lattice dynamics study of bismuth telluride (Bi${}_2$Te${}_3$) up to 23 GPa together with an experimental and theoretical study of the optical absorption and reflection up to 10 GPa. The indirect bandgap of the low-pressure rhombohedral (R-3$m$) phase (α-Bi${}_2$Te${}_3$) was observed to decrease with pressure at a rate of −6 meV/GPa. In regard to lattice dynamics, Raman-active modes of α-Bi${}_2$Te${}_3$ were observed up to 7.4 GPa. The pressure dependence of their frequency and width provides evidence of the presence of an electronic-topological transition around 4.0 GPa. Above 7.4 GPa a phase transition is detected to the $C$2/m structure. On further increasing pressure two additional phase transitions, attributed to the C2/c and disordered bcc (Im-3$m$) phases, have been observed near 15.5 and 21.6 GPa in good agreement with the structures recently observed by means of x-ray diffraction at high pressures in Bi${}_2$Te${}_3$. After release of pressure the sample reverts back to the original rhombohedral phase after considerable hysteresis. Raman- and IR-mode symmetries, frequencies, and pressure coefficients in the different phases are reported and discussed.

• Received 8 June 2011

DOI:https://doi.org/10.1103/PhysRevB.84.104112