Anomalous electronic states of hollandite-type transition-metal oxides

Abstract

We make the electronic structure calculations of transition-metal oxides with the hollandite-type crystal structure A2M8O 16 using the generalized gradient approximation (GGA) in the density functional theory, where the Hubbard-type repulsive interaction is taken into account (GGA+U). We first discuss generic electronic structures of the 3d (M=Ti, V, Cr, Mn) and 4d (M=Mo, Ru, Rh) series of the materials and then consider the origins of the metal-insulator transition observed in K2Cr 8O16 and quasi-one-dimensional electron conduction observed in K2Ru8O16. We also consider in particular the observed metal-insulator transition in K2V 8O16.