In order to obtain abetter understanding of the oxide ion conductivity in perovskites, the structure of La(0.9)Sr(0.1)Bo(9)Mg(0.1)O(3 - delta), B=Al, Ga and Sc, have been investigated by time-of-flight powder neutron diffraction at room temperature, 270, 470, 750, 850 and 950 degreesC. For all compounds, at all temperatures, structural and anisotropic thermal parameters were refined by full profile Rietveld methods to weighted profile R values less than 0.063. The changes in difference nuclear densities, Deltarho, due to changes in temperature are illustrated by difference density maps around the atoms. The observed difference densities are described mainly by zeroth- and second-order spherical harmonics (quadrupolar functions), the nature of which vary with atomic site. The difference density maps provide a direct picture of the average in space and time of changes in atomic thermal vibrations. These observations are less biased by the least-squares method than refined parameters. The largest vibrational changes are found for the oxide ions. The magnitude of vibrational changes corresponds well with the magnitude of the conductivity. The oxide ion site in La0.9Sr0.1Ga0.9Mg0.1O3 - delta has the highest vibrational change and the highest conductivity. (C) 2004 Elsevier B.V All rights reserved.