Structural, dielectric and Raman spectroscopy investigations of Ba${}_{1-x}$Bi${}_{2x/3}$(Fe${}_{0.5}$Nb${}_{0.5}$)${}_{0.025}$Ti${}_{0.975}$O${}_3$ ceramics

This research work reports the structural, dielectric, and Raman scattering studies of Ba${}_{1-x}$Bi${}_{2x/3}$(Fe${}_{0.5}$Nb${}_{0.5}$)${}_{0.025}$Ti${}_{0.975}$O${}_3$ (x = 0-0.15) polycrystalline samples synthesized by the solid state reaction method. The crystalline structure, Raman, and dielectric properties were investigated. The ceramic samples whose compositions x ≤ 0.075 exhibit a tetragonal P4mm symmetry, while the compositions with 0.10 ≤ x ≤ 0.15 crystallize in a cubic phase with a Pm$\overline{3}$m space group. Dielectric studies reveal a transition from classical to relaxor ferroelectrics with an increasing substitution rate x in Ba${}_{1-x}$Bi${}_{2x/3}$(Fe${}_{0.5}$Nb${}_{0.5}$)${}_{0.025}$Ti${}_{0.975}$O${}_3$ ceramics. The relaxor behavior observed for 0.10 ≤ x ≤ 0.15 was highlighted by a significant dielectric anomaly, in which the maximum temperature T${}_m$ was substantially dependent on frequency and went towards low temperature with rising Bi. For the compound x = 0.15, the maximum of ε${}_r^{\prime }$ is around 3000 at room temperature (293 K) and the value of ΔT${}_m$ is 33 K. These values of ε${}_r^{\prime }$ and ΔT${}_m$ are very important for relaxor materials by comparing them with those that are already published in the literature. The relaxor behavior was modeled using the Vogel-Fulcher relation. The Raman spectroscopy analysis demonstrates that the influence of the rate of Ba${}^{2+}$ substitution by Bi${}^{3+}$ may be shown via E (TO${}_2$) and A${}_1$ (TO${}_3$) modes. In the same line, the substantial displacement at the off-centered A location can be attributed to the Bi impurity causing the formation of polar clusters, which drove the transition from classical to relaxor ferroelectrics. This is supported by the stereochemical effect of the 6s${}^2$ lone pair electrons of Bi${}^{3+}$ as well as the significant ionic radius difference between Ba${}^{2+}$ and Bi${}^{3+}$. Furthermore, a thermal study of Raman spectral response to composition backs up our dielectric findings.