Novel In-based high entropy spinel oxides with tunable lattice parameter

A new set of high entropy oxides with spinel structure and variable number of constituents, from five to nine, was prepared keeping the cations in equimolar ratio or reflecting their tendency to occupy octahedral or tetrahedral sites. This approach increases the number of cations into a single phase, leading to larger configurational entropy and to an important unit cell expansion from ∼8.28 to ∼8.55 Å. Among the many cations used, In and Al played a significant role in controlling the lattice parameter, with In producing a relevant unit cell expansion and Al a cell contraction. We demonstrate for the first time the insertion of In into a single-phase high entropy spinel, where it occupies the tetrahedral site, compensated by the inversion of Ni2+ and other divalent cations. Finally, we estimated the cation distribution for each spinel to correlate the dependence of the spinel lattice parameter with the average ionic radius.