A New Cation-Ordered Structure Type with Multiple Thermal Redistributions in Co 2 InSbO 6 .

Cation ordering in solids is important for controlling physical properties and leads to ilmenite (FeTiO 3 ) and LiNbO 3 type derivatives of the corundum structure, with ferroelectricity resulting from breaking of inversion symmetry in the latter. However, a hypothetical third ABO 3 derivative with R32 symmetry has never been observed. Here we show that Co 2 InSbO 6 recovered from high pressure has a new, ordered-R32 A 2 BCO 6 variant of the corundum structure. Co 2 InSbO 6 is also remarkable for showing two cation redistributions, to (Co 0.5 In 0.5 ) 2 CoSbO 6 and then Co 2 InSbO 6 variants of the ordered-LiNbO 3 A 2 BCO 6 structure on heating. The cation distributions change magnetic properties as the final ordered-LiNbO 3 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 3 materials with the R32 structure to be discovered.