# Homogeneity range of ternary 11-type chalcogenides Fe$_{1+y}$Te$_{1-x}$Se$_x$

## TL;DR

This study investigates the chemical homogeneity and effects of excess iron in Fe$_{1+y}$Te$_{1-x}$Se$_x$ superconductors, revealing how Se substitution limits excess Fe and impacts superconductivity.

## Contribution

It provides the first detailed analysis of the homogeneity range and excess Fe influence in Fe$_{1+y}$Te$_{1-x}$Se$_x$ compounds using multiple characterization techniques.

## Key findings

- Maximum excess Fe decreases with more Se substitution.
- Single-phase Fe$_{1+y}$Te$_{1-x}$Se$_x$ cannot be formed with high Se content regardless of excess Fe.
- Superconducting volume fraction is strongly suppressed by excess Fe.

## Abstract

The 11-type Fe-chalcogenides belong to the family of Fe-based superconductors. In these compounds, the interstitial Fe is known to strongly influence the magnetic and superconducting properties. Here we present the chemical homogeneity range of ternary compounds Fe$_{1+y}$Te$_{1-x}$Se$_x$ based on powder x-ray diffraction, energy dispersive x-ray analysis and magnetization measurements. Our investigations show that the maximum amount of excess Fe in homogeneous Fe$_{1+y}$Te$_{1-x}$Se$_x$ decreases with increase in Se substitution for Te. Using our synthesis procedure, single-phase Fe$_{1+y}$Te$_{1-x}$Se$_x$, with $~0.5 \leq x <~1$ could not be formed for any amount of excess Fe. Further, the superconducting volume fraction in the material is found to be strongly suppressed by excess Fe.