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Updated: Jun 4, 2025
08:55
Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses
Published on: June 7, 2018
8.5K
Phase Stability of High Entropy (Mg,Ni,Co,Cu,Zn)O from Temperature-Resolved Synchrotron Diffraction: Tetragonal
Mauro Coduri1,2, Martina Fracchia1,2, Stefano Checchia3
1Chemistry Department, University of Pavia, via Taramelli 16, Pavia, 27100, Italy.
Small (Weinheim an Der Bergstrasse, Germany)
|December 20, 2024
Summary
High entropy oxides containing Mg, Ni, Zn, Co, and Cu undergo structural changes with temperature. Guggenite formation mediates the demixing of these oxides, a novel finding in materials science.
Area of Science:
- Materials Science
- Solid State Chemistry
- Crystallography
Background:
- High entropy oxides (HEOs) exhibit unique properties due to their complex compositions.
- Understanding the thermal stability and phase transformations of HEOs is crucial for their application.
- The role of specific elements, like copper, in HEO structural evolution requires detailed investigation.
Purpose of the Study:
- To investigate the temperature-resolved structure evolution of quinary and quaternary equimolar oxides containing Mg, Ni, Zn, Co, and Cu.
- To elucidate the phase transformations and structural modifications occurring at elevated temperatures.
- To identify the role of copper and magnesium in the demixing process of these HEOs.
Main Methods:
- In situ synchrotron X-ray diffraction was employed to monitor structural changes.
- Equimolar quinary and quaternary oxide compositions were synthesized and analyzed.
- Temperature-dependent structural analysis was performed within the range of 250-500 °C.
Main Results:
- Significant structural modifications were observed at mild temperatures, dependent on elemental composition.
- Quaternary compounds with 0.25 Cu fraction exhibited a tetragonal phase between 250-500 °C.
- Copper fraction influenced the degree of tetragonal distortion; local distortions were observed at 0.20 Cu, absent without copper.
- Upon further heating, the cubic phase was restored, followed by phase segregation.
- In the presence of Cu and Mg, guggenite segregated, acting as a buffer for Cu diffusion to tenorite.
Conclusions:
- The demixing of the prototypal high entropy oxide is mediated by guggenite formation, not solely by tenorite or binary oxides.
- Guggenite facilitates the gradual diffusion of Cu2+ from the cubic high entropy oxide to tenorite.
- The study reveals a new mechanism for the thermal decomposition and phase segregation in complex oxide systems.
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