Thermoelectric properties of a clathrate compound Ba8Cu16P30

We report the electrical resistivity (rho), thermoelectric power (S), thermal conductivity (kappa), and specific heat (C) for the clathrate compound Ba8Cu16P30, in which polyhedral cages are composed of Cu and P atoms. Being in contrast to the n-type conduction in most of clathrate compounds, a p-type metallic conduction in this compound is indicated by the positive S, which monotonically increases up to 65 muV/K at 460 K. The analysis of C(T) gives indirect evidence for low-frequency local vibrations of Ba atoms with two Einstein temperatures 120 and 90 K, respectively. These local vibrations lead to a low lattice thermal conductivity of 2.9 W/K m at 300 K. The combination of the metallic resistivity, large thermoelectric power, and low thermal conductivity, makes this compound be a prospective thermoelectric material. (C) 2003 American Institute of Physics.