Ferroelectric and piezoelectric properties of (Bi1/2Na1/2)TiO3-BiFeO3 ceramics

(1 - x) (Bi1/2Na1/2)TiO3-xBiFeO(3) (x = 0-0.9) ceramics were prepared and the ferroelectric and piezoelectric properties along with the crystal structure were investigated. The crystal system of the ceramics was rhombohedral with the R3c symmetry throughout the compositions. The rhombohedral distortion (90 degrees - alpha), where alpha was the rhombohedral angle based on a pseudocubic perovskite cell, was minimized at x = 0.1, while the lattice constant increased linearly with x. Saturated ferroelectric polarization-electric field hysteresis loops were observed at x = 0-0.6. The coercive field was reduced at x = 0.05-0.2 and the high remanent polarization of 30-35 mu/cm(2) was obtained at x = 0-0.4. The piezoelectric constants d(33) and d(33)* (which was calculated from a unipolar strain-electric field curve) were maximized to 93 pC/N at x = 0.1 and 183 pm/V at x = 0.05, respectively. These results suggested that the increase in the piezoelectric properties was associated with the reduction in the rhombohedral distortion, which could be useful in development of high performance lead-free piezoelectric materials.