Oxygen holes and hybridization in the bismuthates

Abstract

Motivated by the recently renewed interest in the superconducting bismuth perovskites, we investigate the electronic structure of the parent compounds ABiO3 (A = Sr, Ba) using ab initio methods and tight-binding (TB) modeling. We use the density functional theory (DFT) in the local density approximation (LDA) to understand the role of various interactions in shaping the ABiO3 bandstructure near the Fermi level. It is established that interatomic hybridization involving Bi6s and O-2p orbitals plays the most important role. Based on our DFT calculations, we derive a minimal TB model and demonstrate that it can describe the properties of the bandstructure as a function of lattice distortions, such as the opening of a charge gap with the onset of the breathing distortion and the associated condensation of holes onto a1g-symmetric molecular orbitals formed by the O-2pσ orbitals on collapsed octahedra. We also derive a single band model involving the hopping of an extended molecular orbital involving both Bi-6s and a linear combination of six O-2p orbitals which provides a very good description of the dispersion and band gaps of the low energy scale bands straddling the chemical potential.

Bond disproportionation, charge self-regulation, and ligand holes in s−p and in d -electron ABX3

“…As shown in Fig. 5 and 6, for BaBiO 3 , CaFeO 3 and SmNiO 3 , the ligand contribution to the CBM is much larger than that from the B atom, consistent with the previous observation/prediction 17,29,43 , while for CsTlF 3 and CsAuCl 3 , the CBM has almost a similar contribution from the ligand and the B atom. We will further discuss such ligand hole states in Sec.…”

“…We phrase below a number of questions posed regarding disproportionation in ABX 3 compounds, and will address them in this paper by considering six compounds showing DLE behavior, including BaBiO 3 , 9,10,[16][17][18][19][20] (a) What level of electronic structure theory is sufficient to predict the energetic tendency ( Fig. 1…”

“…This view resulted from confusing formal charges assigned on the basis of the extreme ionic view, with physical charge observed in the variational charge density ρ(r). A few recent works have challenged the existence of charge ordering,17,65 suggesting that bond disproportionation, or different local environments, should be a better description of the physical reality.We have analyzed the variational DFT calculated charge density profiles around the B atoms for six structurally relaxed compounds. InFig 3 we plot the total valence charge density of these compounds in a few different ways.…”

Charge density wave modulation in superconducting BaPbO3/BaBiO3 superlattices

“…Doped BaBiO3 (BBO) superconductors possess a commensurate CDW in the parent compound, stable to high temperatures, in an isotropic, nonmagnetic complex oxide. The CDW manifests as bond disproportionation through a frozen breathing mode of the BiO6 octahedra, as pictured in Figure 1(a), with recent experimental and first principle work suggesting hybridization of the BiO6 octahedra plays a dominate role [3][4][5][6]. Doping BBO with Pb in BaPb1-xBiXO3 (BPBO, Tc=11 K) or K in Ba1-xKxBiO3 (BKBO, Tc=30 K) destroys the long range CDW [7][8][9].…”

Raman modes and dielectric relaxation properties of epitaxial BaBiO3 thin films

“…To hybridize with Bi 6s orbitals, only O 2p δ orbitals with A 1g symmetry are allowed. For low energy electronic excitations in BaBiO 3 , Khazraie et al estimated effective hopping integrals for nearest neighbor and next nearest neighbor using a single orbital tight binding model [26]. They showed that with the breathing distortion of A 0.1  and no external electric field, the size of the hopping integral t 1 between nearest neighbors involving oxygen atoms with A 1g symmetry is four times larger than that of the next nearest neighbor hopping integral t 2 between two Bi ions sit at a distance a 2 as shown in figure 6(e).…”