A Raman and far‐infrared investigation of phonons in the rhombohedral V2–VI3 compounds Bi2Te3, Bi2Se3, Sb2Te3 and Bi2(Te1−xSex)3 (0 < x < 1), (Bi1−ySby)2Te3 (0 < y < 1)

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Abstract
The Raman‐active lattice vibrations of Bi2Se3, Bi2Te3, Sb2Te3, and their solid slutions, whose symmetries correspond to the R3m space group, are investigated by Raman scattering. Three of the four expected Raman modes, Eg and A1g, could be determined. The FIR optical properties of Bi2Te3 crystal surfaces of improved quality (E ∥ c and E ⟂ c) and Bi2Se3 (E ⟂ c) are re‐examined near helium and room temperature with a Fourier spectrometer, allowing a determination of the infrared‐active mode frequencies with higher accuracy. The results for Bi2Te3 are compared to the predicted frequencies from the lattice dynamical model, given by Jenkins et al. The frequncy shifts of the Raman‐active modes in the mixed crystals show single‐mode and two‐mode behaviour, which is in agreement with simple models for the substitution of antimony and selenium atoms for bismuth and tellurium, respectively, in Bi2Te3.

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