Hopping transport in doped (Pb0.78Sn0.22)(1-x)InxTe solid solutions

Transport coefficients in (Pb0.78Sn0.22)(1-x)InxTe solid solutions with ind ium content x = 0.03 and 0.05 additionally doped with acceptors (Tl) or don ors (Cl) have been measured and analyzed. The Seebeck coefficient S is posi tive for x = 0.05 in the low temperature range 77-200 K; its sign changes t o negative when the Tl acceptor is added. This unusual behavior of the ther moelectric power can be attributed to hopping conduction at a nonmonotonic energy dependence of the density of localized states. The density-of-states function has been determined at x = 0.03 and 0.05 from experimental data o n the thermopower. Theoretical estimates of the Nernst-Ettingshausen coeffi cient are made for x = 0.03 additionally doped with Cl. The estimates are b ased on taking into account, along with the hopping conduction, the contrib ution from electrons with energies above the mobility edge and on using the critical electrical conductivity exponent obtained in the percolation theo ry. The activation energies characterizing the temperature dependences of c onductivity and Hall and Nernst-Ettingshausen coefficients are discussed an d compared. (C) 2001 MAIK "Nauka/Interperiodica".