Measurement of physical properties of the copper-polytellurides

The anisotropic, two-dimensional structure of a group of quaternary copper polytellurides, A₂BaCu₈Te₁₀, (where A = Rb, Cs or K) appears to fit the description for a `phonon-glass electron-crystal' which is proposed to be a desirable feature of a good thermoelectric material. The structure contains Cu<sub>8</sub>Te<sub>12</sub> pentagonal dodecahedral cages filled with divalent Ba atoms which have the ability to `rattle' within the cages. The resistivity, thermopower and heat capacity of polycrystalline copper-polytellurides have been measured over a broad range of temperatures. Electrical resistivity and thermopower were measured from 4 K to 310 K with room temperature values of approximately 1.7-5.6 mΩ-cm and 30-54 μV/K respectively. Heat capacity was measured from 2 K to 300 K giving Debye temperatures of approximately 310-355 K. Substitutional doping experiments associated with the Te sites in the structure as well as the Ba sites have been done, and the results on the transport measurements are presented. Thermal conductivity and Hall coefficient measurements have also been made on selected samples.