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

Prediction of new high entropy materials presents a significant challenge. Here, the authors combine experimental and computational methods to search for new high entropy oxides in the tetravalent AO(2) family and show why (Ti, Zr, Hf, Sn)(2) crystallizes in a alpha-PbO2 structure. 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 AO(2) family, using exclusively d(0) and d(10) cations. Our aim is to explain the phase stability of the alpha-PbO2 structure, which is found for the medium entropy oxide (Ti, Zr, Hf, Sn)O-2. Using a pairwise approach to approximate the mixing enthalpy, we confirm that alpha-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 alpha-PbO2 structure can be used to understand its stability among tetravalent HEOs.