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Highly (001)-oriented Cu 2- y Se thin films with tunable thermoelectric performances have been grown by pulsed laser deposition. By using targets with different Cu/Se ratios that further determines the copper deficiency of as-grown films, the carrier concentrations of as-grown films are tuned within a broad range from 10 18 to 10 21 cm −3 . The optimum performance is observed at carrier concentration ~1.58×10 20 cm −3 . The distinct properties of Cu 2- y Se thin films with nearly ideal chemical stoichiometric ratio are observed. In addition, a weak change in the electrical transport during the second-order phase transition was observed in the thin films due to the anisotropic structure of the Cu 2- y Se. [ABSTRACT FROM AUTHOR]

Abstract: P-type compounds Cu2Ga x Sn1 − x Se3 (x =0.025, 0.05, 0.075) with a diamond-like structure were consolidated using hot pressing sintering (HP) and spark plasma sintering (SPS) techniques. High-temperature thermoelectric properties as well as low-temperature Hall data are reported. Microstructural analysis shows that the distribution of Ga is homogeneous in the samples sintered by HP but inhomogeneous in the samples sintered by SPS, even with an electrically isolating and thermally conducting BN layer during the sintering. The Seebeck coefficients of the samples sintered by HP and SPS show similar dependence on the carrier concentration and are insensitive to the composition inhomogeneity. In contrast, the composition inhomogeneity results in lower carrier mobility and thus lower electrical conductivity in the samples sintered by SPS than those sintered by HP. Lattice thermal conductivity is further reduced through Ga doping; however, this effect is weakened by the inhomogeneous distribution of Ga. Due to their larger carrier mobility and lower lattice thermal conductivity, the samples sintered by HP exhibit 15–35% higher thermoelectric figure of merits (ZT) than those SPS samples with a high Ga doping level and without the coated BN layer, in which the composition homogeneity is worse. A ZT value of 0.43 is obtained for the HP Cu2Ga0.075Sn0.925Se3 sample at 700K. [Copyright &y& Elsevier]

Abstract: Thermoelectric effects and related technologies have attracted a great interest due to world-wide energy harvesting. Thermoelectricity has usually been considered in the context of stable material phases. Here we report that the fluctuation of structures during the second-order phase transition in Cu2Se semiconductor breaks the conventional trends of thermoelectric transports in normal phases, leading to a critically phase-transition-enhanced thermoelectric figure of merit zT above unity at 400K, a three times larger value than for the normal phases. Dynamic structural transformations introduce intensive fluctuations and extreme complexity, which enhance carrier entropy and thus the thermopower, and strongly scatter carriers and phonons as well to make their transports behave critically. [Copyright &y& Elsevier]