Critical role of cationic local stresses on the stabilization of entropy‐stabilized transition metal oxides

• Published in: Journal of the American Ceramic Society 2020-05, Vol.103 (5), p.3416-3424
• Main Authors: Bhaskar, Lalith K., Nallathambi, Varatharaja, Kumar, Ravi
• Format: Article
• Language: English
• Subjects: Cations; Copper; Crystallites; Entropy; entropy‐stabilized oxide (ESO); internal stresses; lattice defects; Metal oxides; Molecular dynamics; Phase stability; precipitation; Stress distribution; Transition metal oxides
• ISSN: 0002-7820; 1551-2916
• DOI: 10.1111/jace.17029

Entropy‐stabilized transition metal oxides ([MgNiCoCuZn]O) (ESO) in recent years have received considerable attention owing to their unique functional properties. Solution combustion and solid state syntheses resulted in crystallites varying from 5‐15 nm to 3‐5 μm respectively. Phase stability studies showed that all the systems containing Cu2+ ions in the ESO lattice segregated upon slow cooling in the furnace. It was only when ESO was quenched in air from 1000°C the lattice stabilized to a single phase. Experiments concomitant with molecular dynamics (MD) simulations demonstrated that the local stress fields around the cations played a critical role in stabilizing the single phase. The local stress fields are a result of Jahn‐Teller distortion induced by the Cu2+ ions in the lattice. It is clearly established that in the absence of the minimization of the local stress fields around the Cu2+ ions, segregation leading to the formation of a multi‐phase material is imminent for this particular composition. Cationic stresses playing a critical role in the stabilization of entropy‐stabilized transition metal oxide.