Effect of multi-component at the A site on the phase and sintering resistance of high entropy rare earth zirconates

A series of high entropy rare earth zirconate ceramics, (5A0.2)2Zr2O7, with single-or dual-phase structures were synthesized using the solid-state reaction method. The cations at the A site varied in terms of average ionic radius RA, atomic mass MA, radius (size) disorder delta R, and mass disorder delta M. Our results demonstrate that increasing the structural disorder degree promotes the transition from an ordered pyrochlore structure to a defective fluorite structure, and leads to poor sintering resistance. The structural disorder degree of the high entropy zirconates could be increased by decreasing the ionic radius ratio RA/RZr, increasing the size disorder delta R and introducing Ce4+ at the A site. Meanwhile, large size disorder leads to strong partitioning of rare earth ions and deviation of the lattice constant from the predicted value. The presence of Ce4+ ions at A site could significantly increase the structural disorder degree and promote the sintering process, and the underlying mechanisms are proposed and discussed.