In this paper, we report the stabilization of the delta-phase of Bi2O3 thin films from room temperature (RT) to 500 degrees C by the addition of tantalum ions. The delta-Bi2O3 phase is the material presenting the highest ionic conductivity; as bulk it is stable in a reduced temperature range from 730 to 825 degrees C, while the alpha-phase is the RT stable phase. However, when produced by atomic aggregation methods as a nanometric thin film, the delta-phase can be maintained at atmospheric conditions and it actually reverts to the alpha-phase only after thermal annealing, such transformation usually occurs around 250-350 degrees Cby passing through the beta-phase. In this work, we report that tantalum addition during the deposition of the Bi2O3 films by magnetron sputtering allows the maintenance of the delta phase up to 500 degrees C upon thermal annealing in air. (C) 2013 Elsevier B.V. All rights reserved.