Microstructure-electromechanical property correlations in rare-earth-substituted BiFeO3 epitaxial thin films at morphotropic phase boundaries

Structure-electromechanical property correlations in rare-earth (RE)-substituted (001) BiFeO3 (BFO) epitaxial thin films have been investigated. Quantitative piezoelectric coefficient (d(33)) and dielectric constant (epsilon(33)) measurements, in conjunction with selected area electron diffraction, reveal that the enhancement in d(33) and epsilon(33) at the morphotropic phase boundary (MPB) of the RE-substituted films (RE=Dy3+, Gd3+, and Sm3+) is correlated with the presence of a competing intermediate antipolar phase with the rhombohedral ferroelectric and nonpolar orthorhombic phase. This leads to a complex nanoscale phase coexistence at the MPB. Extending the studies to RE=La3+ case, we find the nanoscale phase coexistence to be less pronounced. This explains the lack of increase in d(33) for the La3+-substituted BFO films, in contrast to the Dy3+, Gd3+, and Sm3+-substituted films. (C) 2010 American Institute of Physics. [doi:10.1063/1.3520642]