High Temperature Decomposition of Entropy-Stabilized Oxide (MgCoNiCuZn)O

Entropy-stabilized oxides represent a unique class of single-phase, multicomponent oxides that achieve stability through a substantial configurational entropy, ΔS_conf, which counters a positive, unfavorable enthalpy. Although it is generally postulated that entropy-stabilized oxides will exhibit robust thermal stability due to the presence of the -TΔS_conf term in Gibbs’ free energy, their behavior at high temperatures remains largely unexplored. In this presentation, I will discuss the stability of the prototypical entropy-stabilized oxide, rocksalt (MgCoNiCuZn)O, in the 1300-1700 °C range in air. As temperatures exceed 1300 °C, a gradual reduction in the Cu and Zn content within the rocksalt phase is observed. We pose that the correlated partial loss of these elements is mediated by local distortions and defects that facilitate greater diffusion rates for these ions at elevated temperatures.