  We present the temperature- and thickness-dependent structural and
morphological evolution of strain induced transformations in highly-strained
epitaxial BiFeO3 films deposited on LaAlO3 (001) substrates. Using
high-resolution X-ray diffraction and temperature-dependent
scanning-probe-based studies we observe a complex temperature- and
thickness-dependent evolution of phases in this system. A thickness-dependent
transformation from a single monoclinically distorted tetragonal-like phase to
a complex mixed-phase structure in films with thicknesses up to ~200 nm is the
consequence of a strain-induced spinodal instability in the BiFeO3/LaAlO3
system. Additionally, a breakdown of this strain-stabilized metastable
mixed-phase structure to non-epitaxial microcrystals of the parent rhombohedral
structure of BiFeO3 is observed to occur at a critical thickness of ~300 nm. We
further propose a mechanism for this abrupt breakdown that provides insight
into the competing nature of the phases in this system.
