A piezoelectric perovskite mixed oxide compound has the general formula (BiFeO.sub.3).sub.x--(PbTiO.sub.3).sub.1-X and contains up to 5 at % lanthanum or other rare earth substitution, in which x has a value in the range 0.5 to 0.9. Such compounds are capable of withstanding gas turbine operating temperatures and are suitable for use in sensing and actuation functions in aerospace and other applications.