Nature of the Bottom t_2g-Block Bands of Layered Perovskites. Implications for the Transport Properties of Phases Where These Bands Are Partially Filled

The electronic structure of a series of double layer (Sr₃V₂O₇, KLaNb₂O₇, Li₂SrNb₂O₇, RbLaNb₂O₇, Rb₂LaNb₂O₇) as well as triple layer (Ca₄Ti₃O₁₀, K₂La₂Ti₃O₁₀, Sr₄V₃O_9.7, CsCa₂Nb₃O₁₀) Dion−Jacobson and Ruddlesden−Popper phases and quadruple layer A_nB_nO_3n+2 phases (Sr₂Nb₂O₇ as well as the low-temperature and room-temperature structures of Sr₂Ta₂O₇) has been studied by means of a first-principles density functional theory approach. The results are rationalized on the basis of a simple tight-binding scheme, which provides a simple yet precise scheme allowing the correlation of the crystal structure details and the nature of the bottom t_2g-block band levels. Both the quantitative and the qualitative approaches are used to analyze the nature of the carriers in intercalated samples of the d⁰ semiconducting phases as well as those of the metallic d^x (0 < x ≤ 1) systems. The Ruddlesden−Popper and Dion−Jacobson materials with partially filled t_2g-block bands must be genuine two-dimensional metals except when the M−O_ap distances of the outer layer octahedra are similar and the band filling is not low. The conducting electrons in these phases are almost equally distributed among the different layers. It is shown that the A_nB_nO_3n+2 phases with partially filled bands are potentially interesting materials because they are structurally two-dimensional materials exhibiting one-dimensional band structure features. Finally, the possible application of the simple scheme to related materials such as layered perovskite oxynitrides and the effect of disorder are briefly discussed.