Effect of Ba2+ Doping on the Crystal Structure and Optical Band Gap of NdFeO3 Orthoferrite

In this study, neodymium was substituted by divalent barium ion (Ba²⁺) at various concentrations (x = 0, 0.1, 0.2, 0.3, and 0.4) in the neodymium orthoferrite structure, forming the composition Nd₁₋ₓBaₓFeO₃ via the sol–gel method. To evaluate the effects of Ba²⁺ substitution, detailed structural and optical characterizations were conducted at room temperature. The results indicated that, with increasing barium content, the unit cell volume, the average Fe–O–Fe bond length, and the tolerance factor exhibited an increasing trend. In contrast, the orthorhombic strain and the octahedral distortion angle of the FeO₆ decreased progressively with higher Ba²⁺ concentrations. These structural changes suggest a reduction in lattice distortion, indicating a gradual evolution of the crystal symmetry toward a higher-symmetry (tetragonal) phase. Furthermore, optical characterization revealed a significant reduction in the optical band gap, decreasing from 2.15 eV for the NdFeO3 sample to 1.28 eV for the sample with x = 0.4. This reduction can be attributed to modifications in the electronic structure and the enhancement of optical properties induced by Ba²⁺ substitution. These findings highlight the potential of Ba-doped NdFeO₃ for real world applications, including visible light photo-catalysis, gas and chemical sensors, optoelectronic devices, and photo-electrochemical systems.