Relaxor behavior of $BaBi_4Ti_3Fe_{0.5}Nb_{0.5}O_{15}$ceramics

Monophasic $BaBi_4Ti_3Fe_{0.5}Nb_{0.5}O_{15}$ (BBTFN) which exhibited relaxor ferroelectric properties has been synthesized via the solid-state reaction route. X-ray powder diffraction (XRD) studies carried out at room temperature confirmed the phase to be an n=4 member of the Aurivillius family of oxides. The XRD pattern was indexed to an orthorhombic cell associated with lattice parameters a = 5.463(3) \AA, b = 5.443(3) \AA and c = 41.77(2) \AA. A broad dielectric peak associated with the frequency dependent dielectric maximum temperature was observed. The high temperature slope of the dielectric peak was characterized by the Lorenz-type quadratic law for relaxors. The dielectric relaxation was modeled using the Vogel-Fulcher relationship with activation energy $E_a = 0.014 \pm 0.002 eV$ and freezing temperature $T_{VF} = 558 \pm 1 K.$. Relaxor behavior and the incidence of ferroelectric hystersis (P vs E) loop at room temperature suggested the coexistence of long-range polar ordering with the polar nanoregions induced by compositional fluctuations