Structural phase transitions and their influence on Cu+ mobility in superionic ferroelastic Cu6PS5I single crystals

TL;DR

This study investigates how structural phase transitions in Cu6PS5I single crystals affect Cu+ ion mobility, revealing phase-dependent conductivity changes and diffusion pathways through experimental structural analysis.

Contribution

It provides detailed insights into the structural phase transitions and their impact on Cu+ ion conductivity in Cu6PS5I crystals, including the influence of copper stoichiometry.

Findings

Phase transition at 274K causes a sharp increase in electrical conductivity.

Cu+ diffusion paths are identified via atomic displacement factors.

Structural symmetry changes correlate with conductivity anomalies.

Abstract

The structural origin of Cu+ ions conductivity in Cu6PS5I single crystals is described in terms of structural phase transitions studied by X-ray diffraction, polarizing microscope and calorimetric measurements. Below the phase transition at Tc=(144-169) K Cu6PS5I belongs to monoclinic, ferroelastic phase, space group Cc. Above Tc crystal changes the symmetry to cubic superstructure, space group F-43c (a=19.528); finally at 274K disordering of the Cu+ ions increases the symmetry to F-43m, (a=9.794). The phase transition at 274K coincides well with a strong anomaly in electrical conductivity observed in the Arrhenius plot. Diffusion paths for Cu+ ions are evidenced by means of the atomic displacement factors and split model. Influence of the copper stechiometry on the Tc is also discussed.