Influence of Thallium on the Shubnikov - de Haas effect and Thermoelectric Properties of Sb₂Te₃ and Bi₂Se₃

Influence of Tl-doping on the Shubnikov de Haas effect (SdH) at T=4.2 K in magnetic field up to 38 T of p-Sb_2-xTl_xTe₃ (x=0; 0.005; 0.015; 0.05) and n-Bi_2-xTl_xSe₃ (x=0, 0.01; 0.02; 0.04; 0.06) single crystals has been investigated. By increasing the Tl content, the frequency of the SdH effect and hence the extremal cross-sections of the Fermi-surface decreases in both materials. The hole concentration decreases in Sb_2-xTl_xTe₃ due to a donor effect of Tl and the electron concentration decreases in n-Bi_2-xTl_xSe₃ due to an acceptor effect of Tl. Temperature dependence of the Seebeck coefficient S, electrical conductivity σ, thermal conductivity k and the figure of merit ZT single crystals were measured in the temperature range 77 K - 300 K. The values of k and σ decrease due to Tl doping in Sb_2-xTl_xTe₃ and n-Bi_2-xTl_xSe₃ and the Seebeck coefficient S for all compositions increases in the whole temperature range. The figure of merit ZT increases in both materials. The preferential scattering mechanism in Tl-doped samples changes from the acoustic phonon scattering to the ionized impurity scattering