Microstructure-electromechanical property correlations in rare-earth-substituted BiFeO_3 epitaxial thin films at morphotropic phase boundaries

摘要

Structure-electromechanical property correlations in rare-earth (RE)-substituted (001) BiFeO_3 (BFO) epitaxial thin films have been investigated. Quantitative piezoelectric coefficient (d_(33)) and dielectric constant (ε_(33)) measurements, in conjunction with selected area electron diffraction, reveal that the enhancement in d_(33) and ε_(33) at the morphotropic phase boundary (MPB) of the RE-substituted films (RE=Dy~(3+), Gd~(3+), and Sm~(3+)) 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 =La~(3+) case, we find the nanoscale phase coexistence to be less pronounced. This explains the lack of increase in d_(33) for the La~(3+)-substituted BFO films, in contrast to the Dy~(3+), Gd~(3+), and Sm~(3+)-substituted films.