  Charge dynamics of (Ti1-xVx)2O3 with x=0-0.06 has been investigated by
measurements of charge transport and optical conductivity spectra in a wide
temperature range of 2-600K with the focus on the thermally and doping induced
insulator-metal transitions (IMTs). The optical conductivity peaks for the
interband transitions in the 3d t2g manifold are observed in the both
insulating and metallic states, while their large variation (by ~0.4 eV) with
change of temperature and doping level scales with that of the Ti-Ti dimer bond
length, indicating the weakened singlet bond in the course of IMTs. The
thermally and V-doping induced IMTs are driven with the increase in carrier
density by band-crossing and hole-doping, respectively, in contrast to the
canonical IMT of correlated oxides accompanied by the whole collapse of the
Mott gap.
