Enhanced thermoelectric properties of polycrystalline CuCrS2-xSex (x = 0, 0.5, 1.0, 1.5, 2) samples by replacing chalcogens and sintering

The optimization of thermoelectric properties of the CuCrS2-xSex (x = 0, 0.5, 1.0, 1.5, 2) samples was achieved by substitution in anionic sublattice and sintering at high temperature. The maximum power factor PF ~ 0.3 mW/m•K^2 among a series of samples with chalcogen substitution was obtained for CuCrS0.5Se1.5 sample at T=300 K. The sintering made it possible to obtain the maximum value PF ~ 2.1 mW/m•K2 for CuCrSe2 sample. This is due to a more than threefold increase in the thermoelectric power S(T) in CuCrSe2 sample with a spin-orbital interaction in comparison with CuCrS0.5Se1.5 sample with the same optimal electrical conductivity σ (σ300K ~ 100 S/cm), but without spin-orbital interaction. In CuCrSe2 sample, sintering effectively reduced the s to an optimal value, suppressed of the magnetic phase transition in the range of 50-100 K, and the weak localization were replaced by weak antilocalization indicating the appearance of strong spin-orbit interaction below 20 K. As a result, an additional contribution to the S(T) appeared due to the filtration of current carriers caused by the strong spin-orbit interaction. The effect of grain boundaries on the properties σ(T) and S(T) of the samples was investigated. It was established that polycrystalline samples with a high sulfur content were low-conductivity materials consisting of high-conductivity crystallites with the charge carriers concentration n ~ 1020 cm-3 separated by low-conductivity grain boundaries with fluctuation-induced tunneling conductivity. Both the replacement of sulfur with selenium and sintering led to a decrease in the energy barriers connecting grain boundaries. Selenium-dominated samples (CuCrS0.5Se1.5 and CuCrSe2) had high electrical conductivity with negligible energy barriers between grain boundaries. Logarithmic quantum corrections to the electrical conductivity was observed below 20 K, which indicated a quasi-two-dimensional electron transport in these samples.