Study of the regulatory mechanism of Hf4+ doping on the structural evolution and ferroelectric properties of BiFeO3 thin films

In this study, Hf 4+ -doped BiFe 1− x Hf x O 3 ( x  = 0–1.5 mol%) thin films were synthesized via the sol–gel method, and the effects of Hf doping on the structural and electrical properties were systematically investigated. The results reveal that 1.2-mol% Hf incorporation induces lattice distortion and grain refinement, significantly suppressing the formation of oxygen vacancies. Consequently, the Fe 3+ /Fe 2+ ratio increases to 2.03, and the relative concentration of oxygen vacancies decreases to 0.14. Under an applied electric field of 100 kV/cm, the leakage current density is reduced to 2.98 × 10 –6 A/cm 2 , while the remanent polarization reaches 93.92 μC/cm 2 . The dielectric constant is enhanced to 171, showing stable frequency dependence. Aging tests indicate a low polarization degradation rate of only 10.5%, and the optical band gap is widened to 2.60 eV. These results demonstrate that Hf 4+ doping synergistically improves the overall performance of BiFeO 3 thin films through defect suppression and lattice regulation. This work clarifies the mechanism by which Hf 4+ doping enhances the ferroelectric properties of BiFeO 3 films by inhibiting oxygen vacancy formation and optimizing the lattice structure, thereby providing a solid experimental foundation for the development of low-leakage, high-stability ferroelectric memory devices.