The structural and vibrational properties of bismuth selenide (Bi 2 Se 3 ) have been studied by means of x-ray diffraction and Raman scattering measurements up to 20 and 30 GPa, respectively. The measurements have been complemented with ab initio total-energy and lattice dynamics calculations. Our experimental results evidence a phase transition from the low-pressure rhombohedral (R-3m) phase (α-Bi 2 Se 3 ) with sixfold coordination for Bi to a monoclinic C2/m structure (β-Bi 2 Se 3 ) with sevenfold coordination for Bi above 10 GPa. The equation of state and the pressure dependence of the lattice parameters and volume of α and β phases of Bi 2 Se 3 are reported. Furthermore, the presence of a pressure-induced electronic topological phase transition in α-Bi 2 Se 3 is discussed. Raman measurements evidence that Bi 2 Se 3 undergoes two additional phase transitions around 20 and 28 GPa, likely toward a monoclinic C2/c and a disordered body-centered cubic structure with 8-fold and 9-or 10-fold coordination, respectively. These two high-pressure structures are the same as those recently found at high pressures in Bi 2 Te 3 and Sb 2 Te 3 . On pressure release, Bi 2 Se 3 reverts to the original rhombohedral phase after considerable hysteresis. Symmetries, frequencies, and pressure coefficients of the Raman and infrared modes in the different phases are reported and discussed.

Spectrum of -Bi 2 Te 3 at 13.3 GPa and the corresponding fit of Voigt profiles corresponding to the Raman-active modes of the C2/m structure.

are narrow bandgap semiconductors with tetradymite crystal structure (R-3m) which have been extensively studied along with their alloys due to their promising operation as thermoelectric materials in the temperature range between 300 and 500 K. Studies on these layered semiconductors have increased tremendously in the last years since they have been recently predicted and demonstrated to behave as 3D topological insulators. In particular, a number of high-pressure studies have been done in the recent years in these materials. In this work we summarize the main results of the high-pressure studies performed in this family of semiconductors to date. In particular, we review recent results that address the main characteristics of the pressure-induced electronic topological transition and structural phase transitions observed in this family of compounds. Future high-pressure studies to be performed on these 3D topological insulators are also commented.

American Physical SocietySegura, A.; Panchal, V.; Sánchez-Royo, JF.; Marín-Borrás, V.; Muñoz-Sanjosé, V.; Rodríguez-Hernández, P.; Muñoz, A.... (2012). Trapping of three-dimensional electrons and transition to two-dimensional transport in the three-dimensional topological insulator Bi2Se3 under high pressure. Physical Review B. 85:195139-1-195139-9. doi:10.1103/PhysRevB.85.195139. Abstract. This paper reports an experimental and theoretical investigation on the

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