Structural and dielectric properties of Bi4Ti2Nb0.5Fe0.5O12 ceramics

Monophasic Bi4Ti2Nb0.5Fe0.5O12(BTNF) was synthesized via the conventional solid-state reaction route. The X-ray diffraction (XRD) studies carried out on the as synthesized powdered samples at room temperature confirmed the phase to be an n = 3 member of the Aurivillius family of oxides. The XRD pattern was indexed to an orthorhombic cell associated with the lattice parameters a = 0.5437 ( 2 ) nm , b = 0.5433 ( 2 ) nm and c = 3.306 ( 1 ) nm. Selected area electron diffraction (SAED) studies revealed the presence of superlattice reflections at half-integral positions with respect to the basal plane suggesting cell doubling accompanied by octahedral tilt around the c -axis. Scanning electron microscopic studies carried out on the sintered ceramic (1050 ∘C/2 h) indicated that it consisted of randomly oriented disc-shaped grains. The dielectric properties of the ceramics have been studied in the 30–750 ∘C temperature range at various frequencies (100 Hz to 1 MHz). A dielectric anomaly was observed at 630 ∘C for all the frequencies corresponding to the ferroelectric to paraelectric phase transition. AC conductivity was found to obey Jonscher’s universal law of relaxation. Activation energies obtained from the Arrhenius plot showed different values above and below the transition temperature, suggesting the presence of two different conduction mechanisms.