Influence of Ni doping on microstructural, optical and dielectric properties of lanthanum-based chromite

In this work, LaCrO₃ (LCO) and LaCr_0.5Ni_0.5O₃ (LCNO) chromite samples are synthesized through sol-gel auto-combustion method. The effect of nickel content in LaCrO₃ is studied with respect to their structural, optical and dielectric properties. X-ray diffraction (XRD) confirmed the single-phase orthorhombic crystal structure with space group (Pnma) of both the samples. The obtained lattice parameters and bond lengths via Rietveld refinement analysis are found to be increased with Ni content. The crystallite sizes of LCO and LCNO are calculated using Scherrer's equation, which are found to be 22 nm and 28 nm, respectively. The Fourier-transform infrared (FTIR) spectroscopy of both the samples confirmed the different functional groups and having two main characteristic bands at 420 and 620 cm⁻¹. Scanning electron microscopy (SEM) shows the variation in the surface morphology with Ni doping. Energy-dispersive X-ray (EDX) spectroscopy confirm the elemental compositions of the samples with their nominal atomic and weight percentages. UV–Visible spectroscopy reveals the decrease in the band gap energy from 2.60 eV to 2.30 eV with Ni doping. Raman spectra of LCO and LCNO samples, confirmed the formation of single-phase orthorhombic structure. The Raman active modes are also shifted with Ni doping due to lattice strain and crystal defects. Photoluminescence (PL) absorption intensities are varied, which is due to the creation of defects with Ni doping in LCO crystal structure. The electronic states of constituent element are obtained using X-ray photoelectron spectroscopy (XPS). Dielectric constant (εʹ), loss, and a.c. conductivity (σ_ac) are studied based on the Ni²⁺/Ni³⁺ substitution in LCO at Cr site.