Influence of impurities on the thermoelectric properties of layered anisotropic PbBi4Te7 compound: Experiment and calculations

The kinetic coefficients of high-quality single crystals of ternary layered n-PbBi4Te7 compounds have been measured in the temperature range of 77-400 K. These crystals, doped with electroactive Cd and Ag impurities, were grown by Czochralski pulling with melt supply through a floating crucible. A significant anisotropy of the thermoelectric properties is found. The means of incorporation of electroactive impurities into the ternary compound lattice is established. The experimental values of the Nernst-Ettingshausen coefficient have been analyzed together with the Seebeck, Hall, and conductivity data. The features of transport phenomena in PbBi4Te7 can be explained within the single-band model of nonparabolic energy spectrum and mixed mechanism of electron scattering from acoustic phonons and the Coulomb potential of impurities. It is suggested that acoustic phonon scattering is dominant along the cleavage plane, whereas the impurity scattering dominates along the trigonal axis.