  Mixed-valent perovskite oxides based on BaBiO3 (BBO) are, like cuperates,
well-known high-Tc superconductors. Recent ab inito calculations have assigned
the high-Tc superconductivity to a correlation-enhanced electron--phonon
coupling mechanism, stimulating the prediction and synthesis of new
superconductor candidates among mixed-valent thallium perovskites. Existing
superconductivity has meant that research has mainly focused on hole-doped
compounds, leaving electron-doped compounds relatively unexplored. Here we
demonstrate through ab inito calculations that BBO emerges as a topological
insulator (TI) in the electron-doped region, where the spin-orbit coupling
(SOC) effect is significant. BBO exhibits the largest topological energy gap of
0.7 eV among currently known TI materials, inside which Dirac-type topological
surface states (TSSs) exit. As the first oxide TI, BBO is naturally stable
against surface oxidization and degrading, different from chalcoginide TIs. An
extra advantage of BBO lies in its ability to serve an interface between the
TSSs and the superconductor for the realization of Majorana Fermions.
