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-binary systems GeTe-Bi2Te3, SnTe-Bi2Te3 and PbTe-Bi2Te3 have been prepared and characterised by X-ray powder diffraction analysis. Lattice parameters have been determined and compared with literature data. At room temperature all the samples exhibit a high carrier concentration in the range 3.4 x 10(19) - 2.6 x 10(20) cm(-3). All A(IV)Bi(4)Te(7) and PbBi2Te4 compounds possess 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 gap of Ge(Sn)Bi4Te7 and Ge(Sn)Bi2Te4 compounds were 0.19-0.22 eV as determined from the temperature dependence of electrical resistivity in the intrinsic 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 assessment of the potential of these materials for thermoelectric application has also been made. (C) 2000 Elsevier Science Ltd. All rights reserved.