Investigation of the chemical versatility in high-entropy pyrochlores

This article reports on the exploration of the chemical versatility of entropy-stabilized pyrochlores (A₂B₂O₇) with large chemical disorder introduced on the B site, as well as the study of isovalent and aliovalent substitution on the B site and of Ca²⁺-doping on the A site. Among all the 20 new compounds obtained in this study, 8 are entropy-stabilized: RE₂(TiZrHfGeSn)₂ (with RE = Gd–Ho and Y), Pr₂(TiZrHfScNb)₂O₇, and RE₂(TiGeSnAlNb)₂O₇ (with RE = Er and Y). Moreover, some physical properties (magnetic, electrical, thermal, and optical properties) of these high-entropy pyrochlores have been screened, and some of them could be potentially interesting for applications. For example, we observed low thermal diffusivity values (between 0.4 and 0.7 m² s⁻¹) making them interesting for thermal barrier coating or tunable optical bandgaps in the visible region that could make them appealing as photocatalysts or in optical applications. Furthermore, single-phased compounds were obtained for almost all the rare earths (REs) on the A site. Therefore, when five nonmagnetic cations are used for the B site, it enables to study the magnetic properties and, more specifically, the influence of the local chemical and structural disorder on the exotic ground states observed in monocationic RE pyrochlores.