Broad-Range Tuning of Ferroelectric Switching of LaxBi1-xFeO3 Epitaxial Films via Digital Doping using Off-Axis Co-Sputtering

TL;DR

This study demonstrates precise La doping control in BiFeO3 films, revealing a sharp ferroelectric-to-paraelectric transition at high La concentrations, enabling new opportunities in complex oxide heterostructure engineering.

Contribution

It introduces a digital doping method for tuning La concentration in BiFeO3 films and maps the ferroelectric phase boundary up to x=0.60.

Findings

Ferroelectric switching persists up to x=0.35

Sharp phase transition occurs between x=0.35 and 0.37

Highest La concentration with ferroelectric order reported

Abstract

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 $\geq$ 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.