Structure and electrical properties of Sb2Te3 and Bi0.4Sb1.6Te3 metastable phases obtained by HPHT treatment

We have obtained the metastable phase of the thermoelectric alloy Bi_0.4Sb_1.6Te₃ 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 °C. We have consequently performed comparative studies with the similar phase of Sb₂Te₃. The polycrystalline X-ray diffraction patterns of these phases are similar to the known monoclinic structure α-As₂Te₃ (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?450 K 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 380 K in the metastable phase of Sb₂Te₃ and up to 440 K in the metastable state of Bi_0.4Sb_1.6Te₃. Above these temperatures, the p-type conductivity proper to the initial phases dominates.