  We report in situ characterized TiO2 thin-films deposited on optical fiber,
having thicknesses in the 20-100nm range, and having enhanced conductivity
values of 700S/cm upon interacting with hydrogen. This conductivity was
achieved in pure hydrogen at 800-900C, having a measured activation energy of
0.26eV of the hopping type. Given the variability in the observed results, it
is postulated that the highest conductivity achievable may be much greater than
what is currently demonstrated. The conductivity is retained after cooling to
ambient temperatures as confirmed by Hall measurements, and subsequent
grazing-incidence x-ray diffraction and TEM measurements show the films to be
in the rutile phase. The exceptional conductivity in these films is
hypothesized to result from direct proton incorporation into the lattice
populating the conduction band with excess electrons, or from altering the
Titania lattice to form conductive Magneli phases. The films did not display
any evidence of transformations, however formation of Magneli phases was
confirmed for powders. These interesting results, observed by examining 20nm
films on the surface of optical fiber in combination with the first impedance
spectroscopy performed on films on optical fiber in high temperature Fuel Cell
type environments, confirm hypotheses arrived at in prior publications where
thin-films of Titania had optical properties which could only be explained by
the current claim. Titania thin-films on optical-fiber are being explored for
high temperature hydrogen derived energy generation, thermo-photonic energy
conversion, and associated sensors due to their unique interactions with
hydrogen.
