Structural study of Cu$_{2-x}$Se alloys produced by mechanical alloying

TL;DR

This study investigates the crystalline structures of Cu$_{2-x}$Se alloys produced by Mechanical Alloying, revealing phase transformations and structural details using X-ray diffraction and Rietveld refinement, highlighting the effects of heat treatment.

Contribution

It provides detailed structural analysis of Cu$_{2-x}$Se alloys produced by Mechanical Alloying and elucidates phase evolution mechanisms through experimental data.

Findings

Presence of superionic high temperature phases in as-milled samples

Transformation to a different superionic phase after heat treatment

Low Cu ion occupancy in the transformed phase

Abstract

The crystalline structures of superionic high temperature copper selenides Cu$_{2-x}$Se ($0 \le x \le 0.25$) produced by Mechanical Alloying were investigated using X-ray diffraction (XRD) technique. The measured XRD patterns showed the presence of the peaks corresponding to the crystalline superionic high temperature $\alpha$-Cu$_2$Se phase in the as-milled sample, and its structural data were determined by means of a Rietveld refinement procedure. After a heat treatment in argon at 200$^\circ$C for 90 h, this phase transforms to the superionic high temperature $\alpha$-Cu$_{1.8}$Se phase, whose structural data where also determined through the Rietveld refinement. In this phase, a very low occupation of the trigonal 32(f) sites ($\sim 3$%) by Cu ions is found. In order to explain the evolution of the phases in the samples, two possible mechanisms are suggested: the high mobility of Cu ions in superionic phases and the intense diffusive processes in the interfacial component of samples produced by Mechanical Alloying.