Defect structure and conductivity behaviour are discussed in the solid solution Bi3Nb1-xYxO7-x(0.0 <= x <= 1.0). Investigations were carried out using a combination of ac impedance spectroscopy and powder X-ray and neutron diffraction. Low temperature conductivity and activation energy both increase as a function of x. The former is attributed to an increase in oxide ion vacancy concentration, whereas the latter is due a redistribution of oxide ion vacancies as determined by neutron diffraction measurements. The defect structures at room temperature and 800 degrees C are presented. Curvature in Arrhenius plots of conductivity throughout the composition range is associated with a temperature dependent redistribution of oxide ions. (c) 2006 Elsevier B.V. All rights reserved.