Crystal chemistry of rare-earth containing garnets: Prospects for high configurational entropy

Materials with high degrees of lattice configurational entropy are being studied to assess their potential as highly-stable materials with potentially new and unusual properties. This report involves an assessment of the prospects for producing novel, complex multi-component oxide compounds that have the garnet crystal structure. We examine the crystal chemistry of garnets in an effort to determine if it may be possible to design so-called “high-entropy oxide” garnets, i.e., garnets containing numerous cation components, such that the compounds are stable, monophasic, and offer the potential for new and unusual physical properties. In this report, we quantify configurational entropy for compounds such as garnet that possess numerous cation sublattices. Then, we consider coordination polyhedra and details of bonding in rare-earth containing garnets, in an effort to predict structural aspects of multi-component oxide garnets. • Oxide configurational entropy is the sum of intra-plus inter-sublattice disorder. • A -site polyhedra volumes in rare-earth garnets are 2–8 times B -site polyhedra volumes. • B -site polyhedra do not change volume with changes in garnet rare-earth cations. • A -O bond lengths and strengths are unusually small and large, respectively, in garnet. • Mixing small ​+ ​large B -site cations enables incorporation of numerous A -site cations.