Composition, structure, bonding and thermoelectric properties of \u201cCuT2P3\u201d and \u201cCuT4P3\u201d, members of the T1\u2212x(CuP3)x series with T being Si and Ge

摘要

Through electron microprobe analysis, X-ray and neutron diffraction, it has been established that \u201cCuT2P3\u201d and \u201cCuT4P3\u201d (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 \u201cCuT2P3\u201d and \u201cCuT4P3\u201d 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 T1-x(CuP3)x. The Cu\u2013P ratio of 1 : 3 provides 4 e- per atom and optimizes the atomic interactions. Thermoelectric performance of \u201cCuSi2P3\u201d, \u201cCuGe2P3\u201d and \u201cCuGe4P3\u201d 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 \u201cCuSi2P3\u201d is semiconducting with a narrow band gap. The ZT values are bigger for the Ge-containing phases and reach values of 8.49 \ua5 10-3 for \u201cCuGe2P3\u201d and 1.09 \ua5 10-2 for \u201cCuGe4P3\u201d at room temperature.