COMBINATORIAL DISCOVERY OF A MORPHOTROPIC PHASE BOUNDARY IN A LEAD-FREE PIEZOELECTRIC MATERIAL
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BiFeO3 (BFO) is known to display rich and intricate multiferroic and chemical properties. It has high switchable polarization and piezoelectric properties similar to PbTiO3, but it also suffers from high coercive fields and high leakage currents. This has prompted investigations of doped-BFO as novel solid solutions which may emulate the performance of PbZr1-xTixO3 (PZT) in the composition range of 0.48 < x < 0.52, where a morphotropic phase boundary (MPB) resides and displays substantially enhanced piezoelectric and ferroelectric properties. However neither an increase in electromechanical constants as a function of dopant concentration or domain structures indicative of a MPB piezoceramic had been reported in lead-free BFO-based systems prior to this work. There are some guidelines which predict the presence of MPBs, and one can explore novel compositions by systematically searching for similar structural transitions, Yet comprehensive mapping of compositions requires synthesis of an enormously large number of individual samples. We report on the discovery of a lead-free morphotropic (composition dependent, temperature independent) phase boundary with a simple perovskite structure. The combinatorial thin film strategy was used to identify a rhombohedral to pseudo-orthorhombic structural transition which exhibits a ferroelectric to antiferroelectric transition at approximately Bi0.86Sm0.14FeO3. At the morphtropic phase boundary, there is substantial enhancement in the dielectric and piezoelectric coefficient of Bi0.86Sm0.14FeO3 film is comparable to that of Pb Zr0.52Ti0.48O3 thin film. The discovered compound is a strong candidate if a lead-free piezoelectric material.