Infinitely Adaptive Transition-Metal Ordering in Ln2O2MSe2-Type Oxychalcogenides

The origin of transition-metal ordering in Ln2O2MSe2 oxychalcogenides has been revealed by investigating a range of solid solutions. Transition-metal ordering is determined by the relative sizes of [Ln2O2]2+ and [MSe2]2− layers and can be exquisitely tuned by substitution in either layer, leading to an “infinitely adaptive” structural family. The proportion of the inherently smaller corner-shared motif increases as the transition-metal size increases relative to the lanthanide oxide layers