Electronic structure ofBaPb1−xBixO3

Abstract

Electronic-structure calculations have been carried out for representative members of the $\mathrm{Ba}{\mathrm{Pb}}_{1-x}{\mathrm{Bi}}_x{\mathrm{O}}_3$ alloy series with the use of the self-consistent, scalar-relativistic, linear augmented plane-wave (LAPW) method and the virtual-crystal approximation. The study includes LAPW calculations for the high-temperature cubic ($x=0,0.3, 1$) as well as the room-temperature tetragonal ($x=0.3\mathrm{}$) and monoclinic ($x=1\mathrm{}$) phases. The cubic results exhibit nearly-rigid-band—like behavior and feature a ten-band $\mathrm{O}\mathrm{}\left(2p\right)-\left[\mathrm{Pb}\mathrm{}\right(6s),\mathrm{Bi}\mathrm{}(6s\left)\right]$ complex near $E_F$ containing a pair of broad (∼16 eV) $\sigma$-bonding $2p-6s$ subbands that are approximately centered on nonbonding O $2p$ states. $6s-2p$ band overlap and metallic properties are predicted for all $x$ in the cubic phase. The principal features of the cubic band structure survive the tetragonal distortion, predicting a nearly spherical Fermi surface and a low density of states at $E_F$ in the concentration range $0.05\le x\le 0.30$ where high-temperature superconductivity ($T_c\approx 13$ K) is observed. A strong Fermi-surface instability is shown to occur in the terminal ($x=1\mathrm{}$) BaBi${\mathrm{O}}_3$ compound, explaining both the stability of the monoclinic phase as well as its semiconducting properties.