Single-phase forming ability of high-entropy ceramics from a size disorder perspective: A case study of (La0.2Eu0.2Gd0.2Y0.2Yb0.2)2Zr2O7

A newly five-component equimolar high-entropy ceramic – (La0.2Eu0.2Gd0.2Y0.2Yb0.2)2Zr2O7 with a mixture phase of pyrochlore and fluorite structure was successfully synthesized. On this basis, a series of systematically designed and synthesized high or medium-entropy ceramics, accompanied by a large number of previous reports on multi-component rare earth zirconates, were summarized to jointly investigate the single-phase forming ability of high-entropy rare earth zirconates ceramics (HE-RE2Zr2O7 for short) in terms of entropy value and cationic radius difference (δ). Subsequently, the forming process and mechanism of dual-phase solid solution were analyzed. The conclusions indicated that the single-phase forming ability was more determined by the cationic radius difference rather than the entropy value，and the critical value of δ distinguishing single-phase between dual-phase zone was around 5.2%. In addition, the formation of dual-phase solid solution was essentially driven by the size disorder resulting from rattler effect of cations with significant difference in radius. This work is the first report on the single-phase forming ability of HE-RE2Zr2O7 and would pave new ways for predicting the formation of high-entropy phases.