New pressure-induced monoclinic {\beta}-Sb2Te3 phase with sevenfold symmetry

Source: arXiv

ABSTRACT A nanometric Sb2Te3 rhombohedral phase was produced from Sb and Te by
mechanical alloying for 3 hours and its structural stability was studied by
synchrotron X-ray diffraction (XRD) and Raman spectroscopy (RS) measurements as
a function of pressure. A phase transformation from the ambient pressure
rhombohedral phase into a {\beta}-Sb2Te3 monoclinic structure between 9.8 and
13.2 GPa is observed by XRD. This phase transformation is confirmed by the
Raman spectroscopy measurements. The pressure dependence of the volume fited to
a Birch-Murnaghan equation of state gives a bulk modulus B0 = 40.6 +- 1.5 GPa
and B'0 = 5.1 +- 0.6. The bulk modulus of the nano-Sb2Te3 seems to be slightly
smaller than that for its bulk counterpart (44.8 GPa).

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    ABSTRACT: We report an experimental and theoretical lattice dynamics study of antimony telluride (Sb2Te3) up to 26 GPa together with a theoretical study of its structural stability under pressure. Raman-active modes of the low-pressure rhombohedral (R-3m) phase were observed up to 7.7 GPa. Changes of the frequencies and linewidths were observed around 3.5 GPa where an electronic topological transition was previously found. Raman-mode changes evidence phase transitions at 7.7, 14.5, and 25 GPa. The frequencies and pressure coefficients of the new phases above 7.7 and 14.5 GPa agree with those calculated for the monoclinic C2/m and C2/c structures recently observed at high pressures in Bi2Te3 and also for the C2/m phase in the case of Bi2Se3 and Sb2Te3. Above 25 GPa no Raman-active modes are observed in Sb2Te3, similarly to the case of Bi2Te3 and Bi2Se3. Therefore, it is possible that the structure of Sb2Te3 above 25 GPa is the same disordered bcc phase already found in Bi2Te3 by x-ray diffraction studies. Upon pressure release, Sb2Te3 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.
    Physical review. B, Condensed matter 11/2011; 84(17). · 3.77 Impact Factor


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