Structural study in highly compressed BiFeO3 epitaxial thin films on YAlO3

Abstract

We report a study on the thermodynamic stability and structure analysis of the epitaxial BiFeO3 (BFO) thin films grown on YAlO3 (YAO) substrate. First, we observe a phase transition of M-C-M-A-T occurs in thin sample (<60 nm) with an utter tetragonal-like phase (denoted as M-II here) with a large c/a ratio (similar to 1.23). Specifically, MII phase transition process refers to the structural evolution from a monoclinic M-C structure at room temperature to a monoclinic M-A at higher temperature (150 degrees C) and eventually to a presence of nearly tetragonal structure above 275 degrees C. This phase transition is further confirmed by the piezoforce microscopy measurement, which shows the rotation of polarization axis during the phase transition. A systematic study on structural evolution with thickness to elucidate the impact of strain state is performed. We note that the YAO substrate can serve as a felicitous base for growing T-like BFO because this phase stably exists in very thick film. Thick BFO films grown on YAO substrate exhibit a typical "morphotropic-phase-boundary"-like feature with coexisting multiple phases (M-II, M-I, and R) and a periodic stripe-like topography. A discrepancy of arrayed stripe morphology in different direction on YAO substrate due to the anisotropic strain suggests a possibility to tune the MPB-like region. Our study provides more insights to understand the strain mediated phase co-existence in multiferroic BFO system. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4746036]