Herein we report the doping mechanism and impedance study of the Nb-substituted Bi3Ta1-xNbxO7 (0 <= x <= 0.5) prepared via conventional solid-state method at 900 degrees C over 24 h. The substitutional solid solution crystallised in a cubic fluorite structure, space group Fm-3m and with lattice parameter, a = b = c, in the range 5.4477 (+/- 0.0037)-5.4654 (+/- 0.0011) A. An insignificant unit cell expansion was observed with increasing Nb2O5 content and the linear correlation between lattice parameter and composition variable showed that the Vegard's Law was obeyed. Both TGA and DTA analyses confirmed that the (Bi3Ta1-xNbO7)-O-x solid solution was thermally stable as neither phase transition nor weight loss was observed within the studied temperature range, -28 C-1000 degrees C. The electrical conductivities of these samples were found to increase with increasing Nb concentration; the Bi(3)Ta(0.5)Nba(5)O(7) exhibited the highest conductivity, -1.2 x 10(-2) S cm(-1) at 700 degrees C with a low activation energy of 1.03 eV. (C) 2018 Elsevier B.V. All rights reserved.