Tailoring structural and optical responses in rhombohedral La0.67Sr0.33−xCaxMn1−xNixO3 through dual-site doping

Abstract

Perovskite manganites, due to their strong interplay between crystal structure, electronic states, and magnetic ordering, are highly tunable via chemical substitution. In this study, we investigate the effect of low-level co-doping with Ca²⁺ at the A-site and Ni²⁺ at the B-site in rhombohedral La_0.67Sr_0.33MnO₃ (LSMN0), focusing on the composition La_0.67Sr_0.35Ca_0.025Mn_0.975Ni_0.025O₃ (LSMN1). The doping level x = 0.025 was strategically selected to preserve phase stability while inducing measurable modifications in lattice geometry, electronic structure, and optical behavior. Nanocrystalline samples were synthesized via a modified sol–gel route to ensure compositional homogeneity and fine grain sizes. Structural characterization using X-ray diffraction (XRD) and Rietveld refinement confirmed the retention of the rhombohedral Rc phase, with slight variations in lattice parameters and Mn–O–Mn bond angles upon doping. Fourier-transform infrared (FTIR) and Raman spectroscopy revealed modifications in vibrational modes, indicating reduced Jahn–Teller distortions. Optical absorption measurements in the UV-Vis-NIR range demonstrated a band gap widening, decreased Urbach energy, and notable changes in refractive index dispersion and dielectric functions for the co-doped sample. These findings establish a direct correlation between structural refinement and enhanced optical performance, underscoring the potential of dual-site doping as a powerful tool for tailoring perovskite manganites for applications in optoelectronics, photonic devices, and energy-conversion technologies.