Effect of fuels on the autocombustion reaction synthesis of nanocrystalline gadolinium sesquioxide (Gd2O3) powder: evaluation of structure, morphology, optical and electrical properties

Abstract

Nanocrystalline gadolinium sesquioxide (Gd2O3) powders were prepared by the autocombustion technique using three different fuels (citric acid, urea, and oxalyl dihydrazide). The influence of thermodynamic parameters and nature of fuel on structural transformation, phase formation, morphological characteristics, optical and electrical distinctive were comparatively studied for the first time. Gd2O3 prepared using citric acid and urea were well crystalline with cubic structure, whereas oxalyldihydrazide fuel resulted mixed cubic and monoclinic phase. Obtained structural information were further analyzed by computation of reflection intensities from a structural model, often referred to as the Rietveld method. The formation and purity of Gd2O3 nanoparticles were further confirmed by from the Fourier transform infrared (FTIR) spectra. Surface morphology of Gd2O3 favored the formation of large aggregates, instead of loose and porous particles as observed for citric acid and oxalyl dihydrazide. Optical absorption measurements were recorded in the UV-vis-NIR wavelength region and the optical band gap variations with fuel type were discussed. Electrical conductivity mechanisms in the prepared materials were identified using band gap, nearest neighbor hopping, and variable range hopping models. The citric acid- and urea-derived powders only have optical band and nearest neighbor hopping conduction. Magnetization measurements were performed at 300 K, the saturation magnetization, coercivity, and remanence of each sample was calculated and they showed paramagnetism. Photoluminescence spectra of Gd2O3 nanoparticles have been studied and observed spectroscopic features have been correlated with various transitions of Gd3+ ions.