Deterministic dual control of phase competition in strained BiFeO₃: a multiparametric structural lithography approach

The realization of a mixed-phase microstructure in strained BiFeO₃ (BFO) thin films has led to numerous novel effects derived from the coexistence of the tetragonal-like monoclinic phase (T phase) and rhombohedral-like monoclinic phase (R phase). Strong strain and polarization differences between the phases should result in a high level of transformation plasticity, which enables the continuous alteration of the relative proportion of R and T states in response to external forces. Although the potential for utilizing such plasticity to control mixed-phase populations under external stimuli is evident, direct experimental evidence backed by equilibrium predictions has not yet been fully demonstrated. Here we demonstrate deterministic control of mixed-phase populations in an epitaxially strained BFO thin film through the application of localized stresses and electric fields in a reversible manner. The results illustrate and rationalize deterministic control of mixed phases in strained BFO films, which could be crucial in tuning their functional properties. The findings also highlight a new multiparametric technique in the scanning probe lithography toolbox based on tip-assisted electric and strain field manipulation of functional properties that might find application beyond the ferroelectric domain and structural phase lithography.