Study of intrinsic / extrinsic piezoelectric contributions in La-doped 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 ₃₃ > 100 pm V^-1 whilst maintaining a T_c > 450°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 (α_d) between 4.2 and 6.3 ^-18 m²V^-2, considerably lower than that observed in PZT. The huge deviation from observations in PZT and BiFeO₃ – PbTiO₃ outline considerable domain wall locking in BFPT, which has a detrimental effect on the piezoelectric activity in this system.