  LaTiO$_{3+\delta/2}$, NdTiO$_{3+\delta/2}$, and
Nd$_{1-x}$Sr$_{x}$TiO$_{3+\delta/2}$ thin films have been epitaxially grown on
(100)SrTiO$_{3}$ and (100)LaAlO$_{3}$ single crystal substrates by using the
pulsed laser deposition technique. The oxygen pressure during deposition has
been carefully controlled to ensure that the films are lightly doped in the
metal side near the metal-Mott-insulator boundary. A steep drop of the
effective carrier number at low temperatures has been observed in some of the
films, which may correspond to a gradually opening of the Spin Density Wave
(SDW) gap due to the antiferromagnetic spin fluctuations. At elevated
temperatures, a thermally induced decrease of the Hall coefficient can also be
clearly observed. In spite of the fact that these films were prepared from
different materials in varied deposition conditions, the temperature dependence
of their resistance can all be almost perfectly fitted by a small-polaron
coherent conduction model ($R_s(T)=R_s(0)+C\omega_\alpha/\sinh^2(T_\omega/T)$).
Careful investigation on the fitting parameters implies that the frequency of
the phonon coupled to the electrons may be partially related to the lattice
distortion induced by the mismatch strain of the substrates.
