Structural and Dielectric Properties of Zr Doped BiFeO₃ Nanoparticles

In the present work Zr doped BiFeO₃ (BiFe_1-xZr_x O₃, x=0.03, 0.07, 0.10 and 0.15) nanopowders were synthesized by Sol-gel method. The crystal structures of Zr doped BiFeO₃ samples were examined by XRD using CuK_α radiation. XRD patterns confirmed that all the samples were pure without any trace of impurity phase. The XRD patterns for the nanoscale BiFeO₃ have been refined by FULLPROF Rietveld refinement using space group R3c and also lattice parameters, were estimated. The dielectric properties were enhanced by Zr substitution i.e. dielectric constant (ε ‘) increases and dielectric loss (tanδ) decreases with increasing Zr content except for x =0.15 sample. An anomaly, both in dielectric constant and dielectric loss, was found in the vicinity of antiferromagnetic Neel temperature indicating magnetoelectric coupling between electric and magnetic dipoles. In low frequency range, both ε ‘ and tanδ have high values but decrease gradually with the increase in frequency. Space charge conduction is known to be an important contributor to tanδ at low frequencies. The constant values of ε‘ at higher frequencies may be attributed to the electron exchange between Fe²⁺-Fe³⁺ dipole not following alternating field, beyond a certain frequency. Activation energy was estimated from a.c. conductivity vs. temperature curves at various frequencies. The activation energy from 0.3–0.5 eV in the temperature range of 416–476 K corresponds to singly ionized oxygen vacancies and that of 0.8–0.9 eV in the temperature range 694–724 K corresponds to doubly ionized oxygen vacancies. Variation of Z”/Z”_max vs. frequency at different temperatures showed that peak shifted towards higher frequencies with increasing temperature indicating low frequency dispersion in the samples which may be due to the rigidity of dipoles (stronger bonding between the ions) with Zr doping in BiFeO₃.