Photoemission study of monoclinicBaBiO3

Abstract

We present the results of photoemission studies of "valence-disordered" monoclinic BaBi03 in the photon energy range 15 -120 eV. The hne shapes of the valence-band photoemission spectra and the Ba contributions to the valence band are similar to the line shapes of the total density of states and Ba partial density of states, respectively. The Bi 5d core levels show only one peak for each spin-orbit component. Oxygen resonance is observed, demonstrating the existence of empty 0 2p states. These results support a more covalent rather than a simple ionic picture for the electronic states of BaBi03. Our data suggest that the charge Auctuation between the two unequal Bi sites is small. We also discuss the origin of the semiconducting character of the "valence-disordered" Ba-Bi03.

Polaron formation in Bi-deficient BaBiO3

“…2(c) and displays a reasonable agreement with the experimental data for E σ = 0.12 eV and K 0 ak B g d e 2 ν 0 = 5.0 /K. If we take ν 0 = 1.710 13 Hz (the breathing mode vibration frequency [46]), a = 0.437 nm corresponding to this perovskite cell parameter, g d = 3/8 [47] and K 0 = 0.067 nm −1 (L/W ≈ 2 given by our sample geometry and t = 30 nm, as extracted from the TEM analysis of Fig. 1) we obtain a theoretical value K 0 ak B g d e 2 ν 0 = 2.5 /K, in very good agreement with the fitted value, giving consistency to our analysis.…”

“…Bi-O bond distances have been reported as 2.11 and 2.29 Å, respectively [12]. Spectroscopic experiments have failed to resolve valence differences between Bi ions in both crystallographic sites [13,14], while theoretical work suggests a common ≈ +3 state, which has been rationalized in terms of spatially extended Bi-O bonds related to hybridized Bi-6s and O-2p atomic orbitals [15][16][17]. BBO has been proposed to behave as a topological insulator upon electron doping [18], and it was also theoretically suggested to present a 2D electron gas in its Bi-terminated (001) surface [19].…”

Epitaxial growth of perovskite SrBiO3 film on SrTiO3 by oxide molecular beam epitaxy

“…By DFT calculation, Foyevtsova et al recently demonstrates that the bands straddling the Fermi level are in fact strongly hybridized Bi 6s with O 2p molecular orbitals with A 1g symmetry and contain more O 2p character than Bi 6s character, resulting in the bonding states at ∼10 eV below the Fermi energy and the unoccupied antibonding states with holes in O 2p just above and electrons just below the Fermi level [8], serving as an alternate explanation for the semiconducting nature. The existence of empty O 2p states just above the chemical potential forming the conduction band was previously mentioned in experiment without reference to its molecular orbital and symmetry character [19,[21][22][23]. Further experimental studies are required to compare with the recent DFT calculations.…”

Noncuprate superconductors

“…At room temperature semiconducting BaBiO 3 is monoclinic ða % b % c= ffiffi ffi 2 p ; β 5 90:17 Þ, but close to orthorhombic (Chaillout et al, 1985;Cox andSleight, 1976, 1979;cf. Federici et al, 1990;Jeon et al, 1990;Shen et al, 1989). These two compounds form a solid solution series BaPb 12x Bi x O 3 involving cubic, tetragonal, orthorhombic, and monoclinic modifications.…”