Tunable Optical Properties and Relaxor Behavior in Ni/Ba Co-Doped NaNbO3 Ceramics: Pathways Toward Multifunctional Applications

In this study, Ni/Ba co-doped NaNbO3 ceramics (NBNNOx) were synthesized using a solid-state method to explore the effects of Ni2+ and Ba2+ ion substitution on the structural, optical, and dielectric properties of NaNbO3. X-ray diffraction (XRD) confirmed that the ceramics retained an orthorhombic structure, with crystallinity improving as the doping content (x) increased. Significant lattice distortions induced by the Ni/Ba co-doping were observed, which were essential for preserving the perovskite structure. Raman spectroscopy revealed local structural distortions, influencing optical properties and promoting relaxor behavior. Diffuse reflectance measurements revealed a significant decrease in band gap energy from 3.34 eV for undoped NaNbO3 to 1.08 eV at x = 0.15, highlighting the impact of co-doping on band gap tunability. Dielectric measurements indicated relaxor-like behavior at room temperature for x = 0.15, characterized by frequency-dependent anomalies in permittivity and dielectric loss, likely due to ionic disorder and structural distortions. These findings demonstrate the potential of Ni/Ba co-doped NaNbO3 ceramics for lead-free perovskite solar cells and other functional devices, where tunable optical and dielectric properties are highly desirable.