Thermoelectric Properties of the Layered Compound GeBi4Te7 Doped with Copper

The effect of Cu doping (0.05–0.20 at. %) on the thermoelectric and transport properties of the layered compound GeBi₄Te₇ (with a small Ge deficiency) was studied. According to x-ray diffraction data obtained on cleaved (001) surfaces, Cu doping increases the c cell parameter, presumably because some of the Cu atoms are incorporated in the van der Waals gaps between the five- and seven-layer slabs. In addition, Cu doping reduces lattice thermal conductivity and increases electron mobility. The thermoelectric figure of merit of the material with the optimum Cu content (0.05 at. %) is ZT = 0.65 around 330 K.