On the atomic ordering in the B-sublattice of high-entropy perovskites

Abstract

Atomic ordering in perovskites has been the subject of intensive research for decades. With the growing interest in high-entropy perovskites (HEP), the issue of atomic ordering is now reaching a new level of significance. Many multi-cationic perovskites have already been synthesized, and some of them exhibit atomic ordering. Therefore, the problems of estimating the phase transition temperature of atomic ordering, determining the type of emerging atomic order, and the distribution of cations in ordered sublattices need to be addressed. In this work, based on the unstrained elastic cation-anion bonds model, we develop a Monte Carlo calculation scheme of atomic order-disorder phase transitions in the B-sublattice of perovskites with arbitrary composition and apply it to the case of HEP. We find that HEP’s may experience rock-salt type atomic ordering, while preserving considerable configurational entropy and essentially becoming ordered disordered perovskites. For many HEP’s, whose synthesis has been already reported in literature or which await their synthesis, we estimate the phase transition temperature Tod, reduced cubic lattice parameters, and the composition of the ordered sublattices. Finally, we derive a simple relation for the estimation of Tod from normalized standard deviation of the unstrained cation-anion bond lengths of atoms in the B-sublattice, which can be easily calculated.