Perovskite piezoelectric compositions near the morphotropic phase boundary (MPB) are known to exhibit high piezoelectric response. In lead-based ABO 3 compound with B-site disorder, the origin of this enhancement has been associated with the presence of an intermediate monoclinic/orthorhombic state that bridges the adjacent ferroelectric rhombohedral and tetragonal phases. However, the origin of high piezoelectric response in lead-free ABO 3 compounds with A-site disorder has not been conclusively established. We describe a microscopic model derived from comparative analyses of high resolution transmission electron microscopy and neutron diffraction that explains the origin of high piezoelectric response in lead-free MPB compositions of 0.93(Na0.5Bi0.5)TiO3-0. 07BaTiO3. Direct observation of nanotwins with monoclinic symmetry confirmed the presence of an intermediate bridging phase that facilitates a pathway for polarization reorientation. Monoclinic distortions of an average rhombohedral phase are attributed to localized displacements of atoms along the non-polar directions.
Bibliographical noteFunding Information:
The authors gratefully acknowledge the financial support from National Science Foundation (Nano whisker Synthesis and Property measurements) and Office of Basic Energy Sciences, U.S. Department of Energy #DE-FG02-07ER46480 (Microscopy analysis). The authors would also like to thank the Nanoscale Characterization and Fabrication Laboratory, ICTAS, VT for their help in characterization (HR-TEM). Neutron diffraction measurements at Oak Ridge National Laboratory's Spallation Neutron Source were sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.