Notable enlargement of remnant polarization for fatigue-free SrBi4Ti4O15 thin films by La-substitution

La-doped SrBi4Ti4O15, SrBi4–x La x Ti4O15 (SBLT-x, x = 0.00, 0.10 and 0.25), thin films have been successfully prepared by the sol–gel method. Structures, surface morphology and ferroelectric properties were investigated. Compared with undoped SBTi, SBLT-0.10 shows a notable larger remnant polarization (2P r = 46 μC/cm2). Meanwhile, the SBLT-0.10 film shows little change of P nv and −P nv up to 4.4 × 1010 switching cycles, suggesting an excellent fatigue-endurance characteristics.