The Effects of Te^(2−) and I^− Substitutions on the Electronic Structures, Thermoelectric Performance, and Hardness in Melt-Quenched Highly Dense Cu_(2-x)Se
A systematic study has been carried out on the electronic band structure and density of states, crystal structures, thermoelectric properties, and hardness of the Cu_(2-x)Se system with and without Te^(2−) or I^− substitutions for Se^(2−). Density functional theory calculations indicate that stoichiometric Cu_2Se is a zero-gap material, and copper-deficient Cu_(1.875)Se is a p-type conductor. Te^(2–) substitution increases the total density of states at the Fermi level, whereas, the I^− substitution leads to the reduction of the total and partial density of states for both Se and Cu. Highly dense undoped, Te-doped, and I-doped Cu_(2-x)Se bulks have been fabricated by a melt-quenching method which only takes a few minutes. Rietveld refinements of the X-ray diffraction patterns reveal that the unit cells are expanded after doping. All the fabricated bulks are p-type conductors in accordance with band structure calculations, and they all have figure of merit, zT, values over or close to 1.0 at T = 973 K, except for the Cu_(2-x)Te_(0.16)Se_(0.84). Furthermore, the hardness is distinctly improved by the doping approach, with a maximum value of ca. 0.66 GPa for the Cu_(2-x)Te_(0.16)Se_(0.84), which is higher than those of polycrystalline Bi_2Te_3 and PbTe bulks.
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. Received: December 1, 2014; Revised: January 1, 2015; Published online: February 5, 2015. This work is supported by Australian Research Council (ARC) through an ARC Discovery Project (DP130102956, X.L.W), an ARC Professorial Future Fellowship project (FT130100778, X.L.W), and an ARC Linkage Infrastructure, Equipment and Facilities (LIEF) project (LE120100069, X.L.W). L.L.Z thanks the China Scholarship Council (CSC) for scholarship support. The authors would also like to thank Dr. Tania Silver for proof reading of the manuscript.
Supplemental Material - aelm201400015-sup-0001-S1.pdf