Effect of cadmium, silver, and tellurium doping on the properties of single crystals of the layered compounds PbBi4Te7 and PbSb2Te4

We have studied the effects of doping and excess Te on the thermoelectric properties of single crystals of the layered ternary compounds PbBi4Te7 and PbSb2Te4. X-ray diffraction characterization has shown that the crystals have highly disordered structures. The nature of the possible point defects in the compounds has been analyzed. The silver atoms in Ag-doped PbBi4Te7 seem to reside in the van der Waals gaps between the slabs. The introduction of excess Te is shown to markedly reduce the lattice thermal conductivity of both compounds.