High pressure monoclinic phases of Sb2Te3

The effect of pressure on nanostructured rhombohedral alpha-Sb2Te3 (phase I) was investigated using X-ray diffraction (XRD) and Raman Spectroscopy (RS) up to 19.2 and 25.5 GPa, respectively. XRD patterns showed two new high pressure phases (named phases II and III). From a Rietveld refinement of XRD patterns of alpha-Sb2Te3, the unit cell volume as a function of pressure was obtained and the values were fitted to a Birch-Murnaghan equation of state (BM-EOS). The best fit was obtained for bulk modulus B-0 = 36.1 +/- 0.9 GPa and its derivative B'(0) = 6.2 +/- 0.4 (not fixed). Using the refined structural data for alpha-Sb2Te3, for pressures up to 9.8 GPa, changes in the angle of succession [Te-Sb-Te-Sb-Te], in the interaromic distances of Sb and Te atoms belonging to this angle of succession and in the interatomic distances of atoms located on the c axis were examined. This analysis revealed an electronic topological transition (ETT) along the a and c axes at close to 3.7 GPa. From the RS spectra, the full widths at half maximum (FWHM) of the Raman active modes of alpha-Sb2Te3 were plotted as functions of pressure and showed an ETT along the a and c axes at close to 3.2 GPa. The XRD patterns of phases II and III were well reproduced assuming beta-Sb2Te3 and gamma-Sb2Te3 structures similar to those reported in the literature for alpha-Sb2Te3.