Influence of misfit dislocations on the phase transition of iron(<scp>iii</scp>) oxides

Dislocations commonly occur in thin films under large misfit strain due to the accumulation of strain energy, significantly altering the films' properties. This study investigates the microstructure of Fe₂O₃ polymorphs in films of various thicknesses deposited on yttria-stabilized zirconia (001) substrates. The results reveal that the ε-Fe₂O₃ phase is formed and stabilized at thicknesses below a critical threshold of 20 nm. Beyond this threshold, the volume fraction of the ε-Fe₂O₃ phase decreases, and the α-Fe₂O₃ phase begins to emerge. With further increases in thickness, the ε-Fe₂O₃ phase fully transforms into the α-Fe₂O₃ phase. Detailed analysis suggests that this phase transformation is driven by the formation of misfit dislocations at the film/substrate interface, which compensates for the tensile strain induced by the substrate.