Thermoelectric properties and crystal structure of ternary compounds in the Ge(Sn,Pb)Te-Bi2Te3 systems

Polycrystalline samples of stoichiometric ternary compounds in the quasi-bi nary systems GeTe-Bi2Te3, SnTe-Bi2Te3 and PbTe-Bi2Te3 have been prepared an d characterised by X-ray powder diffraction analysis. Lattice parameters ha ve been determined and compared with literature data. At room temperature a ll the samples exhibit a high carrier concentration in the range 3.4 x 10(1 9) - 2.6 x 10(20) cm(-3). All A(IV)Bi(4)Te(7) and PbBi2Te4 compounds posses s negative type of conductivity, while for other compounds it is positive. The Seebeck coefficient and electrical resistivity have been measured over the temperature range 100-800 K. The calculated values of the energy band g ap of Ge(Sn)Bi4Te7 and Ge(Sn)Bi2Te4 compounds were 0.19-0.22 eV as determin ed from the temperature dependence of electrical resistivity in the intrins ic region. The density of state effective masses m* have been estimated for Ge- and Pb-based ternary compounds and are in the range 0.6-1.1m(0). An as sessment of the potential of these materials for thermoelectric application has also been made. (C) 2000 Elsevier Science Ltd. All rights reserved.