ICT2014 Abstracts

        Stoichiometric and over stoichiometric Ag doped Cu₂Se compounds were prepared by melting, annealing, followed by spark plasma sintering compaction. Low and high temperature thermoelectric properties were investigated by measuring the electrical conductivity, Seebeck coefficient, thermal conductivity and Hall coefficient between 2 K and 900 K. Structural analyses was performed by PXRD and SEM-EDX analyses. The Hall & Seebeck coefficients and temperature dependence of electrical conductivity show that all compounds are high degenerate p-type semiconductors. High temperature α-b phase transition in Cu_2-xSe (0< x<0.2) were observed around 400K in measurements of heat capacity, temperature dependent PXRD data, and transport coefficients.  Room temperature PXRD and SEM pattern indicate that there are two main phases, monoclinic a Cu₂Se and hexagonal CuAgSe, in all Ag doped Cu₂Se compounds. Low temperature transport measurements (Hall coefficient, electrical conductivity, carrier mobility) strongly suggest the presence of yet another phase transition in Cu₂Se, Cu_1.98Ag_0.2Se compounds at temperatures between 85 K and 115 K. Based on the transport data we conclude that %1-2 stoichiometric Ag doping have no significant effect on the electronic properties of Cu₂Se while  it is strongly effective on reducing thermal conductivity likely due to enhanced point defect scattering of phonons. The highest ZT value of 1.5 is achieved in Cu_1.98Ag_0.02Se compounds at 900 K.