A New Cation-Ordered Structure Type with Multiple Thermal Redistributions in Co InSbO.

Cation ordering in solids is important for controlling physical properties and leads to ilmenite (FeTiO ) and LiNbO type derivatives of the corundum structure, with ferroelectricity resulting from breaking of inversion symmetry in the latter. However, a hypothetical third ABO derivative with R32 symmetry has never been observed. Here we show that Co InSbO recovered from high pressure has a new, ordered-R32 A BCO variant of the corundum structure. Co InSbO is also remarkable for showing two cation redistributions, to (Co In ) CoSbO and then Co InSbO variants of the ordered-LiNbO A BCO structure on heating. The cation distributions change magnetic properties as the final ordered-LiNbO product has a sharp ferrimagnetic transition unlike the initial ordered-R32 phase. Future syntheses of metastable corundum derivatives at pressure are likely to reveal other cation-redistribution pathways, and may enable ABO materials with the R32 structure to be discovered.