Persistent three- and four-atom orbital molecules in the spinel Al V2 O4

Abstract

Electronic instabilities in transition-metal compounds may lead to ground states containing orbital molecules when direct metal-metal orbital interactions occur. The spinel AlV2O4 was reported to contain V717+ orbital heptamers that emerge below a 700 K charge ordering transition. Our x-ray total scattering analysis of AlV2O4 between 300 and 1100 K reveals a very different picture as the postulated heptamers are found to be pairs of spin-singlet V39+ trimers and V48+ tetramers, and these orbital molecules persist to at least 1100 K in a disordered high-temperature cubic phase.