Role of Covalency on the Metal‐Insulator Behavior of BaPbO3${\rm BaPbO}_3$ and Ba2PbO4${\rm Ba}_2{\rm PbO}_4$

Abstract

Abstract (BPO) and (B2PO) are two sister compounds with identical valence configuration. However, BPO is reported to be metallic, B2PO is known to be gapped. The metallic nature of BPO itself is debated in the literature. A previous combinatorial experimental and theoretical study had claimed octahedral rotations as the reason for metallicity. On the contrary, a recent theoretical study has attributed the octahedral distortions for the gapped behavior. Motivated by these conflicting conclusions, the electronic structure of these two compounds is probed within the framework of density functional theory. It is shown that B2PO has a larger semi conducting gap of 1.4 eV compared to BPO, eventhough there are no octahedral distortions. Using maximally localized Wannier function (MLWF) calculations, it is divulged that the reduction of Pb‐O covalency is the key to opening of bandgap in these systems. It is shown that the cubic phase of BPO is metallic and that the covalency is reduced by the octahedral rotations in non‐cubic phases leading to the opening of pseudo‐gap. Whereas in B2PO the confinement of covalency to 2D layers leads to a semi‐conducting behavior.