Synthesis, characterization and low temperature studies of iron chalcogenide superconductors

TL;DR

This study synthesizes and characterizes iron chalcogenide superconductors, revealing how composition and substitution affect their superconducting transition temperatures and phase transitions.

Contribution

It reports optimized synthesis conditions, detailed characterization, and the effects of element substitution on superconductivity in iron chalcogenides.

Findings

Superconductivity observed at Tc ~8.5 K in FeSe samples.

Tc increases to ~13 K with partial Te substitution.

Fe1.09Te shows a metal-insulator transition at ~82 K.

Abstract

We have synthesized tetragonal iron selenide and telluride superconductors through solid state reaction at 450deg.C and 550deg.C respectively. These synthesis temperatures have been established by optimization. Electrical resistivity and magnetic susceptibility measurements (4.2-300 K) confirm superconductivity with Tc of around 8.5 K in all selenide samples of nominal composition Fe1+deltaSe (delta=0.02-0.22). However, Scanning Electron Microscopy/ Energy Dispersive Spectroscopy studies clearly indicate that the actual stoichiometric ratio of Fe : Se for all the samples synthesized is around 1:1. Also all the samples exhibit identical phase transition temperatures from tetragonal to orthorhombic structure below ~ 100 K implying identical phase composition. The partial substitution of Se by Te leads to an enhancement of Tc to ~ 13 K. The non-superconducting telluride Fe1.09Te exhibits a metal-insulator phase transition at ~ 82 K. Substitution studies of this telluride system by S and Si have in addition been carried out to investigate if chemical pressure induces superconductivity.