Structural, dielectric and Raman spectroscopy investigations of Ba_1–xBi_2x/3(Fe_0.5Nb_0.5)_0.025Ti_0.975O₃ ceramics

Abstract

This research work reports the structural, dielectric, and Raman scattering studies of Ba_1–xBi_2x/3(Fe_0.5Nb_0.5)_0.025Ti_0.975O₃ (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 $\le$ 0.075 exhibit a tetragonal P4mm symmetry, while the compositions with 0.10 $\le$ x $\le$ 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–xBi_2x/3(Fe_0.5Nb_0.5)_0.025Ti_0.975O₃ ceramics. The relaxor behavior observed for 0.10 $\le$ x $\le$ 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 $\varepsilon_{{\text{r}}}^{^{\prime}}$ is around 3000 at room temperature (293 K) and the value of ΔT_m is 33 K. These values of $\varepsilon_{{\text{r}}}^{^{\prime}}$ 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 Ba²⁺ substitution by Bi³⁺ may be shown via E (TO₂) and A₁ (TO₃) 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 6s² lone pair electrons of Bi³⁺ as well as the significant ionic radius difference between Ba²⁺ and Bi³⁺. Furthermore, a thermal study of Raman spectral response to composition backs up our dielectric findings.