BiFeO3 films with in-plane compressive strain of -3.5% were deposited on oxygen-deficient La0.3Sr0.7MnO3-delta buffered SrTiO3(001) substrates. This highly strained BiFeO3 does not relax directly into its rhombohedral parent phase upon increasing the film thickness. Instead, a multi-step path involving structural transitions is observed. The misfit stress is first accommodated by the occurrence of true tetragonal BiFeO3 with c/a ratio of 1.23, then reduced by the transformation to the M-C-type monoclinic structure, and finally alleviated through the M-C-rhombohedral transition. Moreover, this process enables the formation of strain-driven morphotropic phase boundaries at a stress level much lower than the reported threshold of -4.5%. (C) 2014 AIP Publishing LLC.