Improved electromechanical response in rhombohedral BaTiO3

Zr-, Hf-, and KNb-doped BaTiO3 materials were prepared in a composition range that stabilizes the rhombohedral phase above room temperature. These materials were prepared as bulk polycrystalline material using standard solid-state reaction methods. X-ray diffraction was used to confirm the existence of a stable rhombohedral phase while dielectric constant measurements confirmed the expected phase transition temperatures. A piezoelectric coefficient of d(33) = 290-470 pC/N was obtained for Zr- and Hf-doped BaTiO3, compared with d(33) = 75 pC/N for pure BaTiO3. An electrostrictive coefficient of Q(33) = 0.37 m(4)/C-2 was obtained for the KNb-doped material, compared with Q(33)=0-11 m(4)/C-2 for pure BaTiO3. The maximum strain measured for the doped samples was 5-10 times higher than that of pure BaTiO3.