Study of intrinsic/extrinsic piezoelectric contributions in Ladoped BiFeO3-PbTiO3 ceramics using the Rayleigh method

BiFeO3 - PbTiO3 (BFPT) based materials have received interest as high temperature piezoelectrics due to an extremely high T-c of 632 degrees C, and a spontaneous strain >18%; this high strain makes these materials extremely difficult to pole. Doping with small concentrations of La allows materials to be prepared with a d(33) > 100 pm V-1 whilst maintaining a Tc > 450 degrees C. Presented here are results from a Rayleigh analysis of these materials which shows that the extrinsic contribution to the piezoelectric effect is extremely low, providing Rayleigh coefficients (alpha(d)) between 4.2 and 6.3 x 10(-18) m(2)V(-2), considerably lower than that observed in PZT. The huge deviation from observations in PZT and BiScO3 - PbTiO3 outline considerable domain wall locking in BFPT, which has a detrimental effect on the piezoelectric activity in this system.