Structure and electrical properties of Sb_2Te_3 and Bi_(0.4)Sb_(1.6)Te_3 metastable phases obtained by HPHT treatment

摘要

We have obtained the metastable phase of the thermoelectric alloy Bi_(0.4)Sb_(1.6)Te_3 with electron type conductivity for the first time using the method of quenching under pressure after treatment at P = 4.0 GPa and T = 400-850℃. We have consequently performed comparative studies with the similar phase of Sb_2Te_3. The polycrystalline X-ray diffraction patterns of these phases are similar to the known monoclinic structure α-As_2Te_3 (C2/m) with less monoclinic distortion, β ≈ 92°. We have measured the electrical resistivity and the Hall coefficient in the temperature range of T = 77-450K and we have evaluated the Hall mobility and density of charge carriers. The negative Hall coefficient indicates the dominant electron type of carriers at temperatures up to 380K in the metastable phase of Sb_2Te_3 and up to 440K in the metastable state of Bi_(0.4)Sb_(1.6)Te_3. Above these temperatures, the p-type conductivity proper to the initial phases dominates.