Phase-pure bismuth tantalate fluorites were successfully prepared via conventional solid-state method at 900 A degrees C in 24-48 h. The subsolidus solution was proposed with the general formula of Bi3+x Ta1-x O7-x (0 ae x ae 0.184), wherein the formation mechanism involved a one-to-one replacement of Ta5+ cation by Bi3+ cation within similar to 4.6 mol% difference. These samples crystallised in a cubic symmetry, space group Fm-3 m with lattice constants, a = b = c in the range 5.4477(+/- 0.0037)-5.4580(+/- 0.0039) . A slight increment in the unit cell was discernible with increasing Bi2O3 content, and this may attribute to the incorporation of relatively larger Bi3+ cation in the host structure. The linear correlation between lattice parameter and composition variable showed that the Vegard's law was obeyed. Both TGA and DTA analyses showed Bi3+x Ta1-x O7-x samples to be thermally stable as neither phase transition nor weight loss was observed within similar to 28-1000 A degrees C. The AC impedance study of Bi3TaO7 samples was performed over the frequency range 5-13 MHz. At intermediate temperatures, similar to 350-850 A degrees C, Bi3+x Ta1-x O7-x solid solution was a modest oxide ion conductor with conductivity, similar to 10(-6)-10(-3) S cm(-1); the activation energy was in the range 0.98-1.08 eV.