Voigt Profile is Suitable for Impedance Spectroscopic Analysis of BLSF Ceramics

Abstract

In our earlier studies, samarium-modified bismuth layer-structured ferroelectrics (BLSF), namely Sm_xBi_3-x TiNbO₉ (SBTN); (x=0, 0.2, 0.4, 0.6. 0.8, and 1.0), prepared by solid-state reaction method, have shown broad dielectric relaxations. Among all the compositions, Bi_2.6Sm_0.4TiNbO₉ (BST-0.4) has shown a lower tolerance factor, high remnant polarization (Pr) value, and low stretching factor. In addition, the compound has shown interesting broad dielectric relaxation and non-Debye nature. The specific reasons for the broad relaxation remain unclear. To gain more insights, we synthesized multi rare earth ion substituted compounds, namely, Bi_2.6La_0.2Sm_0.2TiNbO₉ (sample A) and Bi_2.6La_0.2Gd_0.2TiNbO₉ (sample B), using the conventional solid-state reaction method. A single impedance spectroscopic approach alone may not be sufficient to explain the asymmetric or non-Debye behavior, therefore Lorentzian, Gaussian, and Voigt fitting were adopted in the present investigation. From the analysis, the Voigt profile (V_f and Vʹ_f) is found to be a valuable alternative tool to understand the broad impedance non-Debye relaxations. Finally, results were corroborated by dc-conductivity data.