Enhanced Thermoelectric Performance of Nonstoichiometric Compounds Cu3-x SbSe4 by Cu Deficiencies

This work revealed that the Cu-deficient ternary compounds Cu3-x SbSe4 free of Te and Pb exhibit enhanced thermoelectric performance. Cu3-x SbSe4 (x = 0, 0.025, 0.050, 0.075) polycrystalline materials with high phase purity were fabricated by a facile method combining mechanical alloying and spark plasma sintering. Effects of Cu deficiencies on crystal structures, microstructures, element chemical states, and thermoelectric properties were systematically studied. High carrier concentration was obtained for the compositions Cu2.95SbSe4 and Cu2.925SbSe4 due to additional Cu vacancies, contributing to a remarkable increase in electrical conductivity. Together with a satisfactorily large Seebeck coefficient above 300 mu V/K, a high power factor of about 890 mu W/m-K-2 at 523 K was achieved for Cu2.95SbSe4 and Cu2.925SbSe4, almost 60% larger than that of the stoichiometric sample with x = 0. The maximum ZT value was increased to 0.50 at 673 K in the Cu2.925SbSe4 sample sintered at a high temperature (703 K); this is the highest value reported so far for the undoped Cu3SbSe4 system.