Synthesis, phase stability, structural and physical properties of 11-type iron chalcogenides

TL;DR

This review summarizes recent experimental studies on FeSe and Fe$_{1+y}$Te, focusing on synthesis, phase stability, and how excess iron influences their structural, magnetic, and transport properties, highlighting their complex phase behaviors.

Contribution

It provides a comprehensive overview of the synthesis, phase transitions, and physical properties of FeSe and Fe$_{1+y}$Te, emphasizing the effects of composition and external parameters.

Findings

FeSe has a tetragonal to orthorhombic transition at 87 K without magnetic order.

Fe$_{1+y}$Te exhibits complex magnetic and structural phase transitions.

Superconductivity in Fe$_{1+y}$Te occurs only after Te substitution with Se.

Abstract

This article reviews recent experimental investigations on two binary Fe-chalcogenides: FeSe and Fe$_{1+y}$Te. The main focus is on synthesis, single crystal growth, chemical composition, as well as on the effect of excess iron on structural, magnetic, and transport properties of these materials. The structurally simplest Fe-based superconductor Fe$_{1+x}$Se with a critical temperature $T_c \approx$ 8.5 K undergoes a tetragonal to orthorhombic phase transition at a temperature $T_s \approx$ 87 K. No long-range magnetic order is observed down to the lowest measured temperature in Fe$_{1+x}$Se. On the other hand, isostructural Fe$_{1+y}$Te displays a complex interplay of magnetic and structural phase transitions in dependence on the tuning parameter such as excess amount of Fe or pressure, but it becomes a superconductor only when Te is substituted by a sufficient amount of Se. We summarize experimental evidence for different competing interactions and discuss related open questions.