Enhanced Electrical Conductivity caused by Phase Transformation and Interfacial Segregation in an Entropy Stabilized Oxide

Research on entropy stabilized oxides (ESOs) has primarily focused on exploring new structures, chemistries, dislocations [1], or unique properties. However, few studies discuss the impact of secondary phases on functionality. Here, electrical transport mechanisms in the canonical ESO (Co,Cu,Mg,Ni,Zn)O were assessed as a function of secondary phase content [2]. When single-phase, the oxide is a small polaron electronic conductor. After heat treatments, Cu-rich tenorite particles form at grain boundaries, which enhances the grain interior rocksalt oxide electronic conductivity due to increased Cu cation vacancies and compensating small hole polarons. While Cu depletion tailors grain interior the conduction mechanism, Cu-rich tenorite grain boundary phases create a pathway for Cu²⁺/Cu³⁺ small hole polarons after longer heat treatment times. The ability to selectively grow secondary phases nucleated at grain boundaries enables tuning of electrical properties in entropy-stabilized and complex concentrated oxides using microstructure design, nanoscale engineering, and heat treatment, paving the way to develop many novel materials.<br/> <br/>[1] Xin Wang, Justin Cortez, Alexander Dupuy, Julie Schoenung, W.J. Bowman (2023) “High entropy oxide (Co,Cu,Mg,Ni,Zn)O exhibits grain size dependent room temperature deformation” <i>Materials Research Letters</i><br/> <br/>[2] Hasti Vahidi, Alexander D. Dupuy, Benjamin X. Lam, Justin Cortez, Pulkit Garg, Timothy J. Rupert, Julie M. Schoenung, and William J. Bowman (In Revision)