A study was made of the electric and magnetic properties of O-deficient Ba5−xLaxNb4−xTixO15−δ phases, prepared by solid-state reaction followed by controlled reduction under a H atmosphere. Extra electrons, added by the formation of O vacancies (δ), introduced localized spins and the magnetic susceptibility could be described by a temperature-independent contribution and a Curie–Weiss term which was associated with Ti3+ formation. The experimental resistivity (ρ) data for the reduced compounds were well-described, over a wide temperature range, by ρ ≈ ATexp[B/T]-¼; which suggested the presence of small polarons in the system. Although all of the samples exhibited electrical insulating behavior, the electrical resistivity decreased by 4 orders of magnitude for intermediate x-values. This was interpreted as being a consequence of the mixing of the localized bands of the Nb and Ti ions; thus favoring the promotion of carriers due to reduction of the band-gap.

Oxygen Vacancy Doping Effect on the Electrical and Magnetic Behavior of Ba5−xLaxNb4−xTixO15. J.M.De Paoli, R.E.Carbonio, R.D.Sánchez: Journal of Physics and Chemistry of Solids, 2007, 68[2], 124-30