Dielectric and ferroelectric properties of Ho-doped BiFeO3 nanopowders across the structural phase transition

We have studied Ho-doped BiFeO 3 nanopowders (Bi 1−x Ho x FeO 3 , x = 0–0.15), prepared via sol-gel method, in order to analyse the effect of substitution-driven structural transition on dielectric and ferroelectric properties of bismuth ferrite. X-ray diffraction and Raman study demonstrated that an increased Ho concentration (x ≥ 0.1) has induced gradual phase transition from rhombohedral to orthorhombic phase. The frequency dependent permittivity of Bi 1−x Ho x FeO 3 nanopowders was analysed within a model which incorporates Debye-like dielectric response and dc and ac conductivity contributions based on universal dielectric response. It was shown that influence of leakage current and grain boundary/interface effects on dielectric and ferroelectric properties was substantially reduced in biphasic Bi 1−x Ho x FeO 3 (x > 0.1) samples. The electrical performance of Bi 0.85 Ho 0.15 FeO 3 sample, for which orthorhombic phase prevailed, was significantly improved and Bi 0.85 Ho 0.15 FeO 3 has sustained strong applied electric fields (up to 100 kV/cm) without breakdown. Under strong external fields, the polarization exhibited strong frequency dependence. The low-frequency remnant polarization and coercive field of Bi 0.85 Ho 0.15 FeO 3 were significantly enhanced. It was proposed that defect dipolar polarization substantially contributed to the intrinsic polarization of Bi 0.85 Ho 0.15 FeO 3 under strong electric fields at low frequencies.