Investigation of the chemical versatility in high‐entropy pyrochlores

Abstract

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.

High-temperature transport properties of entropy-stabilized pyrochlores

“…The first B-site mixed cation entropy-stabilized pyrochlore, with the chemical formula Dy 2 (Ti 0.2 Zr 0.2 Hf 0.2 Ge 0.2 Sn 0.2 )O 7 , was reported by Vayer et al 19 An extension of this work, to explore the chemical versatility in this system, afforded 20 new high-entropy pyrochlores among which 8 are entropy-stabilized: RE 2 (TiZrHfGeSn) 2 (with RE = Gd-Ho and Y), Pr 2 (TiZrHfScNb) 2 O 7 , and RE 2 (TiGeSnAlNb) 2 O 7 (with RE = Er and Y). 20 In this report, we explore the high-temperature transport properties, in dry and humid air, for the parent compound Dy 2 (Ti 0.2 Zr 0.2 Hf 0.2 Ge 0.2 Sn 0.2 ) 2 O 7 and for Ca-doped samples on the Dy site, obtained by sintering in different partial pressures of oxygen, with the general formula (Dy 1−x Ca x )(Zr 0.2 Hf 0.2 Sn 0.2 Ti 0.2 Ge 0.2 )O 7 with x = 0, 0.05, and 0.1.…”