Charge Ordering in the Geometrically Frustrated Spinel AlV₂O₄

Abstract

We have found that spinel AlV 2 O 4 shows a phase transition at ∼700 K with anomalies of transport and magnetic properties. It is clarified that this corresponds to a charge-ordering transition, where the V 2.5+ ions are separated into three V 2.5-δ ions and one V 2.5+3δ ion. This three-one type of charge ordering, which is coupled with rhombohedral distortion along the (111) axis, reduces the high degeneracy of ground states inherent in this spinel structure, and thus can be understood in terms of "charge frustration."