Optical Properties of Nd$_{1-x}$TiO$_{3}$

Infrared optical measurements were performed on the Nd$_{1-x}$TiO$_{3 }$ system of chemically doped transition-metal oxides. By introducing vacancies (x) on Nd sites, the degree of filling of the d-band on Ti can be controlled. For x=0.0, NdTiO$_{3}$, the compound is a Mott-Hubbard insulator, while for x=1/3, Nd$_{2/3}$TiO$_{3}$, there are no d electrons and the compound is a charge-transfer insulator. Two metal-insulator-transitions are expected at x$\sim $0.10 and 0.20. In this paper, we use the infrared spectroscopy to investigate the optical properties and the low-lying electronic structures of the titanium oxide system. The absolute reflectance of the single crystals was measured via an \textit{in situ} gold evaporation technique using a Bruker \textit{IFT 66v/s} spectrometer between 50 and 40 000 cm$^{-1}$. In the metallic phase (x=0.10), we observed an unusual temperature dependence of the Drude and midinfrared spectral weight. Temperature-dependent optical properties of the Nd$_{1-x}$TiO$_{3 }$ system at different doping levels will be presented.