Abstract
Here, we report detailed strain mapping analysis at heterointerfaces of a new multiferroic complex oxide Bi3Fe2Mn2Ox(BFMO322) supercell and related layered structures. The state-of-the-art aberration corrected scanning transmission electron microscopy (Cs-corrected STEM) and the modified geometric phase analysis (GPA) have been used to characterize the self-assembled transitional layers, misfit defects, and, in particular, the biaxial lattice strain distributions. We found that not only a sufficient lattice misfit is required through substrate selection and to be preserved in initial coherent epilayer growth, but also an appropriate interfacial reconstruction is crucial for triggering the growth of the new BFMO322 supercell structure. The observation of new transitional interfacial phases behaving like coherent film layers within the critical thickness challenges the conventional understanding in existing epitaxial growth model.
Highlights
Perovskite oxides exhibit very rich physical properties including high-temperature superconductivity,[1] magnetoresistance,[2,3] multiferroics,[4] and many others
Films directly grown on SrTiO3(STO) single-crystalline substrates give the conventional pseudo-perovskite Bi2FeMnO6 structure;[14] while the BFMO322 supercell structure has been established on LaAlO3(LAO) substrates with a much pronounced lattice misfit.[12]
We focused on the BFMO films, up to a thickness of approximately 40 nm, grown under optimum pulsed-laser deposition (PLD) conditions for high purity layered BFMO phase at a growth temperature of 700 ◦C and a laser pulse rate of 2 Hz
Summary
Perovskite oxides exhibit very rich physical properties including high-temperature superconductivity,[1] magnetoresistance,[2,3] multiferroics,[4] and many others. The conversion of two Bi2O2 layers to three in interlayer II could be related to the formation of in-plane dislocation partials (for details please see Fig. S2 of the supplementary material).[19] it suggests that the crystal structure and very likely the film stoichiometry gradually transfer from a highly distorted pseudo-perovskite one to the BFMO322 supercell through transitional regions I and II.
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