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

Abstract

Abstract The optimization of thermoelectric properties of the CuCrS 2 − x Se x (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·K)−2 for CuCrSe2 sample. This is due to a more than threefold increase in the thermopower S(T) in CuCrSe2 sample with a spin-orbital interaction in comparison with CuCrS0.5Se1.5 sample with the same optimal electrical conductivity σ ( σ ∼ 100 S cm−1), but without spin-orbital interaction. In CuCrSe2 sample, sintering effectively reduced the σ 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 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 ∼ 10 20 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.