Composition, structure, bonding and thermoelectric properties of "CuT2P3" and "CuT4P3", members of the T(1-x)(CuP3)x series with T being Si and Ge.

Through electron microprobe analysis, X-ray and neutron diffraction, it has been established that "CuT(2)P(3)" and "CuT(4)P(3)" (T = Si, Ge) adopt the cubic or tetragonally distorted zinc blende structures in which two element mixtures are present on both atomic sites. One site contains the Cu/T mixture while the other site is occupied by T and P. The structure of "CuT(2)P(3)" and "CuT(4)P(3)" can be derived from that of silicon or germanium, in which the single Si or Ge site is broken into two independent sites by the preferential Cu and P substitution. The phases appear to be members of the extended series with a general formula of T(1-x)(CuP(3))(x). The Cu-P ratio of 1 : 3 provides 4 e(-) per atom and optimizes the atomic interactions. Thermoelectric performance of "CuSi(2)P(3)", "CuGe(2)P(3)" and "CuGe(4)P(3)" was evaluated from low temperatures to 400 K through resistivity, Seebeck coefficient and thermal conductivity measurements. The Ge-containing phases show a metallic-type behaviour and "CuSi(2)P(3)" is semiconducting with a narrow band gap. The ZT values are bigger for the Ge-containing phases and reach values of 8.49 x 10(-3) for "CuGe(2)P(3)" and 1.09 x 10(-2) for "CuGe(4)P(3)" at room temperature.