A fluorine-oxygen substitution has been realized in a PZT material with a composition Pb-0.89(Ba, Sr)(0.11)(Zr0.52Ti0.48)O-3 thanks to the introduction of Mg2+ ions in the B-site of the perovskite. Oxygen vacancies may exist in the anionic sublattice if the fluorine rate is lower than the required one for a stoichiometric PZT-type ABO(3). The F-O substitution makes the relative amount of rhombohedral phase in the MgO and F-doped PZT samples decrease and a drastic increase of the Curie temperature is observed. Minimum values of dielectric constant, high level dielectric losses and piezoelectric coefficient are obtained for a fluorine concentration close to the stoichoimetric PZT one.