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

We have studied Ho-doped BiFeO3 nanopowders (Bi1−xHoxFeO3, 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 Bi1−xHoxFeO3 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 Bi1−xHoxFeO3 (x > 0.1) samples. The electrical performance of Bi0.85Ho0.15FeO3 sample, for which orthorhombic phase prevailed, was significantly improved and Bi0.85Ho0.15FeO3 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 Bi0.85Ho0.15FeO3 were significantly enhanced. It was proposed that defect dipolar polarization substantially contributed to the intrinsic polarization of Bi0.85Ho0.15FeO3 under strong electric fields at low frequencies.