Variation of Piezoelectric properties and mechanisms across the relaxor-like/Ferroelectric continuum in BiFeO3??? (K0.5Bi0.5)TiO3???PbTiO3 ceramics

(1- x - y)BiFeO₃-x(K_0.5Bi_0.5)TiO₃-yPbTiO₃ (BFKBT- PT) piezoelectric ceramics were investigated across the compositional space and contrasted against the xBiFeO₃- (1-x)(K_0.5Bi_0.5)TiO₃ (BF-KBT) system, whereby a range of relaxor-like/ferroelectric behavior was observed. Structural and piezoelectric properties were closely related to the PbTiO₃ concentration; below a critical concentration, relaxor-like behavior was identified. The mechanisms governing the piezoelectric behavior were investigated with structural, electrical, and imaging techniques. X-ray diffraction established that longrange non-centrosymmetric crystallographic order was evident above a critical PbTiO₃ concentration, y > 0.1125. Commensurate with the structural analysis, electric-field-induced strain responses showed electrostrictive behavior in the PbTiO₃-reduced compositions, with increased piezoelectric switching in PbTiO₃-rich compositions. Positive-up-negative-down (PUND) analysis was used to confirm electric-field-induced polarization measurements, elucidating that the addition of PbTiO₃ increased the switchable polarization and ferroelectric ordering. Piezoresponse force microscopy (PFM) of the BF-KBT-PT system exhibited typical domain patterns above a critical PbTiO₃ threshold, with no ferroelectric domains observed in the BF-KBT system in the pseudocubic region. Doping of BiFeO₃-PbTiO₃ has been unsuccessful in the search for high-temperature materials that offer satisfactory piezoelectric properties; however, this system demonstrates that the partial substitution of alternative end-members can be an effective method. The partial substitution of PbTiO₃ into BF-KBT enables long-range non-centrosymmetric crystallographic order, resulting in increased polar order and TC, compared with the pseudocu- ic region. The search for novel high-temperature piezoelectric ceramics can therefore exploit the accommodating nature of the perovskite family, which allows significant variance in chemical and physical characters in the exploration of new solid-solutions.