Chemical-alloying is demonstrated to stabilize the mixed-phase structure of highly strained epitaxial BiFeO 3/LaAlO 3 (001) heterostructures. Such mixed-phase structures are essential for the large electromechanical responses (4%-5% strains under applied electric field); however, films with thickness exceeding 250 nm undergo an epitaxial breakdown to a non-epitaxial bulk-like rhombohedral-phase. Such an irreversible transformation of the mixed-phase structure limits the magnitude of the net surface displacement associated with these field-induced phase transformations. Using high-resolution x-ray diffraction reciprocal space mapping and scanning-probe-based studies, we show that chemical-alloying of BiFeO 3 thin films can stabilize these mixed-phase structures and delay the onset of epitaxial breakdown.
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The authors would like to acknowledge the help and scientific insights of Rick Haasch and Doug Jeffers at the Center for Microanalysis of Materials at UIUC. The work at UIUC was supported by the Army Research Office under grant W911NF-10-1-0482 and by Samsung Electronics Co., Ltd. under grant 919 Samsung 2010-06795. Experiments at UIUC were carried out in part in the Frederick Seitz Materials Research Laboratory Central Facilities, which are partially supported by the U.S. Department of Energy under grants DE-FG02-07ER46453 and DE-FG02-07ER46471.