Electronic Structure of Layered Oxides Containing M₂O₇ (M = V, Nb) Double Octahedral Slabs

The electronic structure of M₂O₇ double octahedral slabs with low d electron counts has been studied. It is shown that the nature of the low d-block bands is strongly dependent on the d electron count and the distortions of the layer. All d¹ systems are expected to be similar and to exhibit Fermi surfaces which result from the superposition of both one-dimensional (1D) and two-dimensional (2D) contributions. For lower d electron counts the electronic structure is quite sensitive to the existence of M-O bond alternations perpendicular to the layer and off-plane distortions of the equatorial O atoms. The Fermi surface of these systems can either be purely 2D or have 1D and 2D portions like those of the d¹ systems. It is suggested that the recently reported phase Rb₂LaNb₂O₇ could be a 2D metal. It is also proposed that chemical reduction of the A'[A_n-1Nb_nO_3n+i] Dion- Jacobson phases with n = 3 could lead to metallic conductivity, in contrast with the results for the n = 2 phases.