Structural modification and piezoelectric properties in Bi0.5Na0.5TiO3-BaTiO3-SrTiO3 thin films

The structure and piezoelectric properties of the (0.935-x)Bi0.5Na0.5TiO3-0.065BaTiO(3)-xSrTiO(3) (BNT-BT-ST) thin films as a function of ST substitution were investigated. The ST substitution was found to induce downward shift of the depolarization temperature (T (d)). The BNT-BT-ST thin films underwent a transition from ferroelectric phase to relaxor pseudocubic phase with the increase of ST content. The increased polarization of the compositions at around x = 0.18-0.20 was related to three possible mechanisms: polarization extension favoured by the simultaneous presence of polar and non-polar phases; the occurrence of electric field-induced transitions from weakly polar relaxor to ferroelectric polar phase; and the enhanced polarizability of the crystal structure induced by the weakening of the Bi-O bond. The enhanced piezoelectric coefficient d (33,f) of 120 pm/V was obtained for the compositions at around x = 0.18-0.20. It was attributed to the phase transition of ferroelectric to relaxor pseudocubic being at near room temperature.