Phase stability of entropy stabilized oxides with the α-PbO2 structure

Abstract

The prediction of new high entropy oxides (HEOs) remains a profound challenge due to their inherent chemical complexity. In this work, we combine experimental and computational methods to search for new HEOs in the tetravalent AO2 family, using exclusively d0 and d10 cations. Our aim is to explain the phase stability of the α-PbO2 structure, which is found for the medium entropy oxide (Ti, Zr, Hf, Sn)O2. Using a pairwise approach to approximate the mixing enthalpy, we confirm that α-PbO2 is the expected lowest energy structure for this material above other candidates including rutile, baddeleyite, and fluorite structures. We also show that no other five-component compound composed of the tetravalent cations considered here is expected to form under solid state synthesis conditions, which we verify experimentally. Ultimately, we conclude that the flexible geometry of the α-PbO2 structure can be used to understand its stability among tetravalent HEOs.