Reduction of the lattice strain with increasing field amplitude in polycrystalline BiFeO3

As dynamic interfaces in piezoelectric materials, domain walls can greatly impact the functionality under applied external fields. Recently, conductive domain walls have been found to result in Maxwell-Wagner (M-W)-like dispersion of the lattice strain and ferroelastic domain wall motion as a function of field frequency in polycrystalline BiFeO3. Here, we reveal an anomalous field-dependent behavior of the ferroelastic domain wall motion and lattice strain during field cycling. This response is dominated by a common nonlinear increase of ferroelastic domain wall motion and an unusual nonlinear reduction of the lattice strain with increasing field amplitude. Using analytical modeling, this complex field-dependent behavior of polycrystalline BiFeO3 is interpreted by the generation of opposing fields accompanying domain wall motion. Two contributors to the opposing fields are charge accumulation and movement along conductive domain walls and elastic coupling between adjacent grains.