Negative thermal expansion induced by coordination number change in high-entropy oxides

Coordination number changes in chemical bonds sometimes produce a gigantic volume change, as exemplified by the α–β transition in tin. We have achieved a giant negative thermal expansion (NTE) using four-to-six coordination number change in high-entropy oxides. Thermal expansion anomalies appear in...

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Bibliographic Details
Published in:AIP advances Vol. 15; no. 11
Main Authors: Iida, N., Kasugai, R., Ikeda, K., Saitoh, K., Ito, D., Katayama, N., Okamoto, Y., Hirai, D., Takenaka, K.
Format: Journal Article
Language:English
Published: Melville American Institute of Physics 01.11.2025
AIP Publishing LLC
Subjects:
Chemical bonds
Coordination numbers
Crossovers
Dilatometry
Entropy
Low temperature
Thermal expansion
X ray powder diffraction
ISSN:2158-3226, 2158-3226
Online Access:Get full text
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Summary:Coordination number changes in chemical bonds sometimes produce a gigantic volume change, as exemplified by the α–β transition in tin. We have achieved a giant negative thermal expansion (NTE) using four-to-six coordination number change in high-entropy oxides. Thermal expansion anomalies appear in the equimolar oxide (MgCoNiCuZn)O in the crossover temperature range from a multiple-phase state including four-coordination at low temperatures to a single-phase state with six-coordination. By changing the cation ratio, a giant NTE occurs with a volume change exceeding 2% at temperatures higher than 800 °C. Furthermore, doping Ca or Na promotes atomic movement accompanying the crossover and also improves volume change reversibility. Comparison of powder x-ray diffraction analysis and dilatometry results demonstrates that the coordination number change induces NTE.
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ISSN:2158-3226
2158-3226
DOI:10.1063/5.0299836