High-resolution EELS study of the vacancy-doped metal/insulator system, Nd1-xTiO3, x=0 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 (x = 0) is a Mott-Hubbard insulator and Nd2/3TiO3 (x = 0.33), a band insulator. The insulator to correlated-metal transitions occur at x approximate to 0.20 and x approximate to 0.10. Both O K- and Ti L-2,L-3-edge data were obtained on the title materials and the related d(0) perovskites, CaTiO3, SrTiO3 and BaTiO3. The crystal structure of Nd0.70TiO3 (x = 0.30) was refined from powder neutron data in Cmmm which is taken as a model for the structure of Nd2/3TiO3 (x = 0.33) as well. The L-edge spectra for Nd1-xTiO3 Show Systematic changes consistent with the valence state evolution from all Ti3+ (x = 0.0) to all Ti4+ (x = 0.33). 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 L-3 and L-2 peak widths for Nd2/3TiO3 than for the other d(0) 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 0 K-edge spectrum for Nd2/3TiO3 is attributed to the involvement of Nd 5d levels. (c) 2005 Elsevier Inc. All rights reserved.