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Ba (barium) and Ti (titanium) co-doped bismuth ferrite (Bi1−xBaxFe1−xTixO3 or BBFT) ceramics with x = 0.050, 0.075, 0.100, and 0.150 are synthesized by tartaric acid modified sol–gel technique. The Rietveld refinement of X-ray diffraction patterns confirms that no structural phase transition exists from rhombohedral to cubic phase by the co-doping of Ba and Ti up to 15%. The average crystallite size reduces from 26.62 nm to 14.30 nm and the lattice strain increases from 0.00379 to 0.00650 with the increase in co-doping concentration. The increase in dielectric constant whereas decrease in loss tangent was observed with an increase in co-doping concentration. The ac conductivity analysis employing Jonscher's universal power law suggests the existence of small polaron hopping (SPH) mechanism and overlapping large polaron tunneling (OLPT) for low and high co-doping concentration respectively. The Arrhenius plots of all samples show that for a particular value of frequency ~104 Hz, ac conductivity of all the samples increases with the increase in temperature. The activation energy is found to lies between 0.14 eV and 0.61 eV. The Nyquist plot represents the effect of grain and grain boundaries in terms of equivalent electrical circuits, which reveals a temperature-dependent relaxation process. The frequency-dependent real and imaginary part of the impedance spectra of sample shows that after a critical frequency ~ 104 Hz, all the curves merges because of increased hopping rate of charge carries, which indicates the existence of negative temperature coefficient of resistance (NTCR). These kinds of variation suggest the improved dielectric properties of BBFT ceramics. Highlights: No crystallographic phase transition was observed up to 15% of co-doping of Ba and Ti in BiFeO3. With increase in co-doping concentration, average crystallite sizes decrease whereas lattice strain increases. SPH and OLPT mechanism are appropriate for low and high co-doping concentrations respectively. Ba and Ti co-doped bismuth ferrite shows the enhanced dielectric properties. [ABSTRACT FROM AUTHOR]

Bismuth ferrite (BiFeO3 or BFO), is an extremely promising multiferroic material having broad range of applications. In the present study, we investigated the optimization of annealing temperature for the preparation of pure phase bismuth ferrite using quantitative Rietveld analysis of XRD patterns. The rhombohedral structure was confirmed by X-ray diffraction with R3c space group as a primary phase (pure BFO) along with a cubic secondary phase (Bi25FeO40) having space group I23. The quantitative analysis of refine data shows the decrease in the values of fitting parameters in case of double refinement and hence convergence towards the best fitting. Also, with the increase in annealing temperature, very nominal decrease in phase percentage of secondary phase was observed. At annealing temperature of 780 °C, the intensity of (110) planes suddenly becomes more in comparison to (104) planes. The average crystallite size of samples was calculated using Scherrer formula, W–H plot method, and Rietveld method, and lattice strain was derived from the W–H plot method. Overall, the crystallite size increases with the increase in annealing temperature. It has been also observed that the strain, lattice parameters, unit cell volume, and effective bond lengths decrease with the increase in annealing temperature, but no significant change was observed in bond angles with the variation in annealing temperature. [ABSTRACT FROM AUTHOR]