Superconductivity and thermal properties of sulphur doped FeTe with effect of oxygen post annealing

Abstract

Here, we report the synthesis and characterization of sulphur-substituted iron telluride i.e. FeTe 1− x S x ; ( x = 0–30 %) system and study the impact of low temperature oxygen (O 2) annealing as well. Rietveld analysis of room temperature X-ray diffraction (XRD) patterns shows that all the compounds are crystallized in a tetragonal structure (space group P4/ nmm) and no secondary phases are observed. Lattice constants are decreased with increasing S concentration. The parent compound of the system i.e. FeTe does not exhibit superconductivity but shows an anomaly in the resistivity measurement at around 78 K, which corresponds to a structural phase transition. Heat capacity C p( T) measurement also confirms the structural phase transition of FeTe compound. Superconductivity appears by S substitution; the onset of superconducting transition temperature is about 8 K for FeTe 0.75S 0.25 sample. Thermoelectric power measurements S( T) also shows the superconducting transition at around 7 K for FeTe 0.75S 0.25 sample. The upper critical fields H c 2(10%), H c 2(50%) and H c 2(90%) are estimated to be 400, 650 and 900 kOe respectively at 0 K by applying Ginzburg Landau (GL) equation. Interestingly, superconducting volume fraction is increased with low temperature (200 °C) O 2 annealing at normal pressure. Detailed investigations related to structural ( XRD), transport [ S( T), R( T) H], magnetization (AC and DC susceptibility) and thermal [ C p( T)] measurements for FeTe 1− x S:O 2 system are presented and discussed.