An approach to correlating the structural, electrical and optical properties of Mn²⁺-modified bismuth sodium...

In the current study, we investigated the structural, electrical, and optical characteristics of Mn-modified BNT ceramic systems with the nominal formula (Bi_0.5Na_0.5)_1-x Mn _x TiO₃, (x = 0.01-0.05), obtained by the solid-state reaction method. The structural analysis using Rietveld refinement suggested a rhombohedral phase with the R3c space group in all samples. Relaxor behavior was observed in all the modified samples, and Mn doping also promoted this behavior. At the same time, lower dielectric loss was noticed in the x = 0.05 ceramics. Detailed electrical characterization was performed through impedance spectroscopy studies. The Nyquist plot was fitted with the proposed RQC-RC circuit and found to be of the non-Debye type. Correspondingly, the grain and grain-boundary resistance values were determined. The AC conductivity data at different temperatures were fitted by the Jonscher's power law equation, σ _tot(ω) = A(T) × ω ^s + σ _dc(T); 0 < s < 1, supporting the correlated barrier hopping (CBH) model. The reduction in optical band gap energy (E _g) obtained from UV-visible spectroscopy and the decrease in the hopping barrier height (W _M) suggest that Mn doping may induce defect states. The results are consistent with possible oxygen vacancy formation, which may contribute to localized hopping conduction in the modified ceramic system. Furthermore, the slim polarization loop confirmed the relaxor behavior observed in the modified samples. The combined results suggest that Mn doping is an appropriate approach for optimizing the functional properties of BNT ceramics, with x = 0.05 as the most favorable in terms of overall performance.