Lock-in spin structures and ferrimagnetism in polar Ni2-xCoxScSbO6 oxides

CoVO3 High-Pressure Polymorphs: To Order or Not to Order?

Materials properties are determined by their compositions and structures. In ABO3 oxides different cation orderings lead to mainly perovskite- or corundum like derivatives with exciting physical properties. Sometimes, a material can be stabilized in more than one structural modification, providing a unique opportunity to explore structure-properties relationship. Here, CoVO3 obtained in both ilmenite-(CoVO3 -I) and LiNbO3 -type (CoVO3 -II) polymorphs at moderate (8-12 GPa) and high pressures (22 GPa), respectively are presented. Their distinctive cation distributions affect drastically the magnetic properties as CoVO3 -II shows a cluster-glass behavior while CoVO3 -I hosts a honeycomb zigzag magnetic structure in the cobalt network. First principles calculations show that the influence of vanadium is crucial for CoVO3 -I, although it is previously considered as non-magnetic in a dimerized spin-singlet state. Contrarily, CoVO3 -II shows two independent interpenetrating antiferromagnetic Co- and ferromagnetic V-hcp sublattices, which intrinsically frustrate any possible magnetic order. CoVO3 -II is also remarkable as the first oxide crystallizing with the LiNbO3 -type structure where both metals contain free d electrons. CoVO3 polymorphs pinpoint therefore as well to a much broader phase field of high-pressure A-site Cobaltites.

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 (FeTiO₃) and LiNbO₃ type derivatives of the corundum structure, with ferroelectricity resulting from breaking of inversion symmetry in the latter. However, a hypothetical third ABO₃ derivative with R32 symmetry has never been observed. Here we show that Co₂InSbO₆ recovered from high pressure has a new, ordered‐R32 A₂BCO₆ variant of the corundum structure. Co₂InSbO₆ is also remarkable for showing two cation redistributions, to (Co_0.5In_0.5)₂CoSbO₆ and then Co₂InSbO₆ variants of the ordered‐LiNbO₃ A₂BCO₆ 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 ABO₃ materials with the R32 structure to be discovered.