Effect of excess Bi on structure and ferroelectric properties of polycrystalline BiFeO3 thin films

Polycrystalline BiFeO3 thin films with overdosed Bi of up to 15 mol% were prepared through chemical solution deposition. All the films crystallized in R3c structure after annealing at 550 °C for 5 h by normal furnace. The analysis of out-of-plane and in-plane X-ray diffraction showed that the lattice constants and in-plane stress of films strongly depended on the amount of excess Bi, where lattice constants were minimums and in-plane stress was a maximum at excess Bi of 5 mol%. The films exhibited the largest saturation polarization of 14.8 μC cm− 2 at excess Bi of 5 mol%, revealing a correlation with the in-plane tensile stress. These results suggested that the excess Bi greatly influenced the polarization properties of BiFeO3 thin films through the lattice distortion induced by the in-plane stress.