Electrical and magnetic properties of nanostructured Ni doped CeO2 for optoelectronic applications

Employing hydrothermal technique, undoped and nickel doped cerium oxide nanoparticles (Ni doped CeO2 NPs) are synthesized with different concentration of dopant (5 M%, 10 M% and 15 M%). Prepared samples are subjected to Powder X-ray diffraction (PXRD), Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDX), High resolution transmission electron microscopy (HRTEM) with selected area electron diffraction (SAED), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), Ultraviolet-visible spectroscopy (UV-vis), Photoluminescence spectroscopy (PL), Vibrational sample magnetometry (VSM), Dielectric and electrical conductivity studies. Formation of CeO2 NPs and Ni doped CeO2 NPs is confirmed by PXRD and EDX. The crystallite size of the samples, determined from powder XRD using Williamson-Hall (W-H) plot, diminishes with increased Ni doping. The lattice parameter variation indicates an initial lattice contraction when the doping is less and a lattice expansion with enhanced Ni doping. These variations in crystallite size and lattice parameter could be due to the replacement of Ce ions by Ni ions in the CeO2 lattice. SEM and HRTEM images show that the morphology of the NPs formed is nearly spherical. The UV-vis spectroscopic studies indicated that bandgap energy of Ni doped CeO2 NPs widens as the Ni dopant concentration is increased. Increase of oxygen vacancy (VO) with increase in Ni concentration is designated by Raman spectra. The PL studies show that the nanoparticles of CeO2 and Ni doped CeO2 exhibit luminescence in the violet-blue-green wavelengths region (400 nm-500 nm). The decrease in emission intensity with increase of Ni concentration is indicative to increase of oxygen vacancies with increase in Ni content which act as non-radiative centers. VSM studies show that all the samples exhibit paramagnetism. The saturation magnetization and the retentivity of the samples increase as the Ni dopant concentration increases. All the samples display frequency dependent dielectric properties. With increase in the concentration of Ni dopant and frequency, a reduction in the values of dielectric constant and dielectric loss and an improvement in the electrical conductivity were observed for all the samples.