  Electric conductivity and structural details of the hole-doped polaron
conductor La0.9Sr0.1FeO3 (LSF10) are reported. The conductivity of a single
crystal shows an exponential increase with temperature with a maxi-mum of 100
S/cm at 700 K and with activation energy of about 375 meV, and a decrease for
higher temperatures that follows a power law. The exponential increase of the
electric conductivity for 300 K {\leg} T {\leg} 700 is accompanied by a shift
of spectral weight in the photoemission valence band towards the Fermi level,
indicative of a strong electron-phonon interaction. The subsequent decrease of
the conductivity for T > 700 K is accompanied by a reversible phase
transformation from orthorhombic to rhombohedral symmetry. The decreasing
conductivity for T > 700 K is likely due to the reduction of the iron due to
oxygen loss causing a decreasing hole concentration, as evidenced by a
substantial chemical shift in the Fe K-shell x-ray absorption spectra. Two
additional fine structures in the conductivity data at 357 K, this is, a small
temperature reversible jump in the conductivity, and at 573 K, a slight
reversible increase of the polaron activation energy, are correlated with an
exceptionally strong decrease in spectral valence band intensity near the Fermi
level, and with the onset of a corresponding structural transition.
