Temperature-driven phase transformations and microstructure evolution in the thermoelectric colusite Cu₂₆V₂Sn₆S₃₂. An...

Area of Science:

• Materials Science
• Solid State Chemistry
• Crystallography

Background:

• Thermoelectric materials require structural stability for optimal performance.
• Colusite-type compounds are promising thermoelectric materials.
• Understanding phase transformations is key to material reliability.

Purpose of the Study:

• Investigate phase transformations in Cu26V2Sn6S32 using in situ HR-SXRPD.
• Elucidate the relationship between synthesis temperature, microstructure, and phase stability.
• Assess the impact of air exposure on material integrity.

Main Methods:

• In situ high-resolution synchrotron X-ray powder diffraction (HR-SXRPD).
• Mechanochemical synthesis followed by annealing at 873 K and 1023 K.
• Analysis of air-aged samples after several months.

Main Results:

• Both samples contained colusite- and sphalerite-type phases, not two distinct colusite phases.
• Minor copper sulfate detected, indicating surface reactivity with air.
• Colusite phase showed discontinuous lattice parameter variations upon heating, linked to sulfate decomposition.

Conclusions:

• The structural evolution of Cu26V2Sn6S32 is significantly influenced by oxygen exposure and sulfate phase decomposition.
• Findings provide insights into thermal stability and degradation mechanisms.
• Guidance for improving the reliability of colusite-based thermoelectric devices is offered.