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 d₃₃ = 290–470 pC/N was obtained for Zr- and Hf-doped BaTiO₃, compared with d₃₃ = 75 pC/N for pure BaTiO₃. An electrostrictive coefficient of Q₃₃ = 0.37 m⁴/C² was obtained for the KNb-doped material, compared with Q₃₃ = 0.11 m⁴/C² for pure BaTiO₃. The maximum strain measured for the doped samples was 5–10 times higher than that of pure BaTiO₃.