A New Cation-Ordered Structure Type with Multiple Thermal Redistributions in Co2InSbO6

Cation ordering in solids is important for controlling physical properties and leads to ilmenite (FeTiO3) and LiNbO3 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 Co2InSbO6 recovered from high pressure has a new, ordered-R32 A(2)BCO(6) variant of the corundum structure. Co2InSbO6 is also remarkable for showing two cation redistributions, to (Co0.5In0.5)(2)CoSbO6 and then Co2InSbO6 variants of the ordered-LiNbO3 A(2)BCO(6) structure on heating. The cation distributions change magnetic properties as the final ordered-LiNbO3 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.