High-resolution EELS study of the vacancy-doped metal/insulator system, Nd1−xTiO3, image to 0.33.

High-resolution electron energy loss spectroscopy (EELS) spectra have been obtained for several members of the vacancy-doped metal/insulator perovskite system Nd1−xTiO3 where NdTiO3 (image) is a Mott–Hubbard insulator and Nd2/3TiO3 (image), a band insulator. The insulator to correlated-metal transitions occur at image and image. Both O K- and Ti L2,3-edge data were obtained on the title materials and the related d0 perovskites, CaTiO3, SrTiO3 and BaTiO3. The crystal structure of Nd0.70TiO3 (image) was refined from powder neutron data in Cmmm which is taken as a model for the structure of Nd2/3TiO3 (image) as well. The L-edge spectra for Nd1−xTiO3 show systematic changes consistent with the valence state evolution from all Ti3+ (image) to all Ti4+ (image). Octahedral crystal fields of 1.5 and 2.0 eV were inferred from the L-edge data for NdTiO3 and Nd2/3TiO3 by comparison with calculated spectra from the literature. Broader L3 and L2 peak widths for Nd2/3TiO3 than for the other d0 perovskites are attributed to the more complex crystal structure of this material which includes two Nd sites with partial occupation and a more distorted Ti–O environment with low site symmetry. A markedly different O K-edge spectrum for Nd2/3TiO3 is attributed to the involvement of Nd 5d levels.