Structural and electronic transport properties in Sr-doped BiCuSeO

We report on the structural and electronic transport properties of BiCuSeO based compounds, that have recently been reported as promising thermoelectric materials with figure of merit ZT > 0.8 at 923 K, and share the same crystal structure as the high-Tc iron based 1111 oxypnictides. We show that the substitution of Bi³⁺ by Sr²⁺ induces a strong decrease of the electrical resistivity up to the solubility limit reached for x = 0.35, which originates from the strong increase of the carriers concentration. Two anomalies in the resistivity curves have been observed, one for the undoped compound near 260 K and the other for the doped samples at very low temperature. However, structural and magnetic measurements do not provide indications of structural or magnetic phase transition or superconductivity as it had been previously suggested in BiCu_1-xOS. We show that the thermoelectric properties of Bi_1-xSr_xCuSeO materials can be well understood through the analysis of the electronic band structure and the density of states close to the Fermi level and we provide possible directions toward the enhancement of the thermoelectric figure of merit of these materials.