Electrical and Magnetic Properties for Bulk FeSe and FeSe 0.5 Te 0.5 Superconductors

We report a one-step low temperature sintering method for preparing high quality FeSe and FeSe 0.5 Te 0.5 polycrystalline superconductors, and investigate their transport and magnetic properties. The low temperature resistance results show that onset temperatures of the superconducting transition for FeSe and FeSe 0.5 Te 0.5 are 11.06 K and 14.72 K, respectively. X-ray diffraction results demonstrate that Te alloying causes expansion of lattice parameters, and density functional theory calculations confirm that Te-5 p orbital electrons are related to the enhancement of the temperature of the superconducting transition. Magnetic measurements reveal that the superconducting diamagnetic transition appears at 9.35 K and 14.16 K for FeSe and FeSe 0.5 Te 0.5 , respectively, in keeping with the initial transition temperature of zero resistivity. In addition, high temperature transport results show that there is a sign crossover in the thermopower for FeSe and FeSe 0.5 Te 0.5 , which is due to the dominant contributions from electrons and holes.