Shift in Morphotropic Phase Boundary in La-Doped BiFeO3–PbTiO3Piezoceramics

Polycrystalline BiFeO3–PbTiO3 (BF–PT) powders with mixed tetragonal and rhombohedral crystal structure (morphotropic phase boundary: MPB) were modified with lanthanum to provide a wide variation in tetragonal distortion. X-ray diffraction from both the powder and the corresponding bulk ceramic demonstrated that the MPB in the bulk is shifted from 1–5 mol % towards the tetragonal PT as compared to the powder. This shift was correlated with the degree of tetragonal distortion as quantified by c/a ratio.