Broad-range tuning of ferroelectric switching of La <i>x</i> Bi1− <i>x</i> FeO3 epitaxial films via digital doping using off-axis co-sputtering

To investigate the scope of ferroelectric behavior in La-substituted BiFeO3 films, LaxBi1−xFeO3 epitaxial films were synthesized using off-axis co-sputtering on SrTiO3(001) and DyScO3(110) substrates with a SrRuO3 bottom electrode layer. A digital-doping deposition method was used to enable precise control and continuous tuning of La concentration in high-quality LaxBi1−xFeO3 films across a wide range of x = 0.05–0.60, which was systematically investigated using piezoresponse force microscopy. Robust and reversible out-of-plane ferroelectric switching has been observed up to x = 0.35, while films with x ≥ 0.37 exhibit no measurable ferroelectric behavior, indicating a sharp ferroelectric-to-paraelectric phase transition between x = 0.35 and 0.37. This represents the highest reported La concentration in LaxBi1−xFeO3 films that retains ferroelectric ordering, highlighting opportunities to engineer ferroelectric and multiferroic properties in complex oxide heterostructures.