Photoemission and inverse-photoemission studies of ${\mathrm{Ba}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{K}}_{\mathrm{x}}$${\mathrm{BiO}}_{3\mathrm{-}\mathrm{y}}$

X-ray and inverse photoemission were used to investigate the occupied and unoccupied electronic states of ${\mathrm{Ba}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{K}}_{\mathrm{x}}$ ${\mathrm{BiO}}_{3\mathrm{-}\mathrm{y}}$. The results show metallic character with a low density of states on either side of $E_F$ and a broad manifold from -13 to 2 eV consisting of Bi-O sp hybrids. Generally good agreement of theory with experiment is found except that the centroid of the calculated Bi-O manifold is ∼1 eV too close to $E_F$ (as for the high-$T_c$ superconductors). Core-level results indicate single chemical environments for O, Ba, and K. The Bi 4f results suggest inequivalent Bi environments. All core-level spectra show energy-loss features shifted ∼1 eV to a higher binding energy relative to the main line. Unoccupied electronic state structures at 4, ∼7, ∼9, and 14 eV reflect Bi 6p, Ba 5d, K 3d, and Ba 4f bands, respectively. Photon emission associated with plasmon decay is observed as a constant energy feature at hν=22.4 eV. Inverse-photoemission resonance studies for incident electron energies that would excite O 2s-2p transitions show no enhancement of the O 2p holes directly above $E_F$.