Thermoelectric properties of doped Bi2Te3, Sb2Te3, Bi2Se3 single crystals and nanocomposits

A short introduction to the thermoelectric figure of merit, thermoelements. Then basic properties of bismuth-antimony tellurides: crystal structure, Drubble-Wolfe model of the Fermi-surface of Bi2-xSbxTe3, Brillouin zone and band structure of Bi2-xSbxTe3. Importance to increase the density of state by impurity bands. it possible to do by doping of Sn or Ga. Increasing of Seebeck coefficient is possible by changing of character of scattering charged carriers. We used magnetic impurity: Fe in Bi2Te3 and Bi2Se3 or Cr in Sb2Te3. Both materials are ferromagnetic at low temperatures. The figure of merit for Sb2-xCrxTe3 at T>150 K is higher than in undoped sample, which is related mainly to a larger Seebeck coefficient for doped crystal. In the last part of my talk, I will discuss new nanocomposite thermoelectric material composed of nanocrystals of Bi-Sb-Te covered by C60 molecules. C60 layers prevent a recrystallization of Bi-Sb-Te nanocrystals during sintering. p-type doping effect of C60: increasing hole density (p-type) and decreasing electrons (n-type) in the nanocomposite Bi-Sb-Te-С60. C60 provide thermal phonons blocking and partly charge transfer in the anocomposite. The figure of merit ZT has increased by 30% up to 1.16 as compared with starting material. We developed a theoretical model which includes different scattering mechanisms.