Thermoelectric response of Fe_xSe_1/2Te_1/2(x=0.95, 1.00, 1.05 and 1.10) superconductors

In the present work we have tried to explore the nature of charge carriers, Fermi temperature, T_F, and superconducting critical temperature, T_c, through the resistance and thermoelectric power measurements of Fe_xSe_1/2Te_1/2 samples. The polycrystalline samples ha ve been prepared with nominal compositions Fe_xSe_1/2 Te_1/2 (x=0.95, 1.00, 1.05 and 1.10) via two step solid state reaction route. X-Ray diffraction results reveal the formation of tetragonal structure in all the samples. The measurements of resistance as a function of temperature show that all the samples are superconducting. The observed superconducting transition temperatures are 12.60 K, 13.68 K, 12.42 K and 12.07 K for x= 0.95, 1.00, 1.05 and 1.10, respectively. The temperature dependent Seebeck coefficient also confirms the superconducting transition in all the samples. From temperature dependent Seebeck coefficient measurements, we have determined the Fermi temperatures and studied the nature of charge carriers. The variation of Seebeck coefficient with temperature gives us idea about the scattering mechanism and multiband character of the samples.