Tuning the charge carrier density in the thermoelectric colusite

The colusite Cu26V2Sn6S32 has high potential as a thermoelectric material at medium-high temperatures because of a large Seebeck coefficient (S similar or equal to 220 mu V/K) and rather small electrical resistivity (rho similar or equal to 100 mu Omega m) at 660 K. To improve the thermoelectric performance, we have tuned the hole carrier density p by substituting Zn for Cu in Cu26-xZnxV2Sn6S32 (x = 1-3) and starting with Cu and Sn deficient compositions in Cu26-yV2Sn6S32 (y = 1, 2) and Cu26V2Sn6-zS32 (z = 0.25-1), respectively. Powder x-ray diffraction and electron-probe microanalysis showed that the Zn-substituted samples and Sn-deficient (z >= 0.5) samples are formed in a single phase, whereas the Cu26-yV2Sn6S32 samples are composed of two phases with slightly different compositions. Within these samples, the value of p at 300K varies in the range between 3.6 x 10(20) and 2.8 x 10(21) cm(-3). The relation between p and S led to the effective mass m* of 4-7m(0) for the hole carriers. The large S of the colusite is therefore ascribed to the heavy mass carriers of the valence band top. The decreases in p with x and y reduced the dimensionless thermoelectric figure of merit ZT, whereas the increase in p with z raised ZT from 0.56 (z = 0) to 0.62 (z = 0.5) at 660 K. Published by AIP Publishing.