Role of Ni2+ substituent on the structural, optical and magnetic properties of chromium oxide (Cr2-xNixO3) nanoparticles

Abstract

Pristine chromium oxide (Cr2O3) and nickel ions (Ni2+) substituted Cr2O3 nanoparticles were synthesized using a simple co-precipitation technique. The main objective of this work is to investigate Ni2+ substituent's role at different concentrations on the structural, morphological, optical, and magnetic properties of Cr2O3 nanoparticles. Structural analyses based on X-ray diffraction (XRD), Raman and Fourier transform infra-red (FTIR) data confirmed the successful incorporation of Ni2+ into Cr2O3 nanoparticles up to x = 0.05 of Ni2+ content, without affecting the rhombohedral crystal structure of Cr2O3 nanoparticles. Rietveld refinement results showed the variation in lattice parameters and cell volumes alongwith the substitution of Ni2+ into Cr2O3 nanoparticles. Raman and FTIR spectra also depicted a considerable shift in the characteristic vibration modes of Cr2O3 nanoparticles due to strain-induced by Ni2+ substitution. Beyond x = 0.05, the structural transformation took place from rhombohedral to cubic crystal structure. Subsequently, new peaks (apart from Cr2O3 phase modes) have been observed at x = 0.1 of Ni2+ content due to the formation of secondary phase i.e., nickel chromate (NiCr2O4). Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) illustrated the changes in the morphology of Cr2O3 nanoparticles with Ni2+ substitution. UV–Vis analysis revealed a narrowing of optical band energy (Eg) of Ni2+ substituted Cr2O3 nanoparticles from 3 to 1.85 eV as Ni2+ content varies from x = 0 to 0.2, respectively. Afterward, there is an increase in optical band gap energy (Eg) when Ni2+ content increased from x = 0.3 to 0.5, as NiCr2O4 started dominating the Cr2O3 phase. Single-phase Ni2+ substituted Cr2O3 nanoparticles exhibited a superparamagnetic behavior, whereas the multi-phase compound ascribed to both superparamagnetic and paramagnetic. These changes in optical and magnetic properties can lead to novel strategies to render applications in the field of optoelectronics and optomagnetic devices.