Phase-field study of precipitate morphology in epitaxial high-entropy oxide films

High-entropy oxides (HEOs) with multiple equal-molar cations may exist as single-phase solid solutions at sufficiently high temperatures. However, such solid solutions are susceptible to the formation of stable or metastable precipitates at lower temperatures. The morphology of such precipitates could have profound influence on the resulting properties. Here, we extended our recently developed phase-field model of simultaneous solid solution and stoichiometric phases for binary alloy systems to multicomponent oxides. Using the stress-free lattice parameters and elastic constants of precipitate phases as well as the interfacial energy between the precipitate and the solid solution matrix from density-functional theory calculations, we performed phase-field simulations to understand the morphology of coherent CuO-rich precipitates in epitaxial Mg_0.2Co_0.2Ni_0.2Cu_0.2Zn_0.2O thin films validated by transmission electron microscopy (TEM) observations. By analyzing the detailed precipitate sizes, orientation, and spatial distributions as well as the stress and strain distributions along different cross-sections, we reveal the important impact of elastic constraints on the CuO precipitate distributions in thin films. These findings can provide useful insights into controlling the coherent precipitate morphology in epitaxial HEO thin films.