The crystalline structure of gadolinium oxide nanoparticles (Gd2O3-NPs) synthesized at different temperatures via X-ray diffraction (XRD) technique

Abstract Sol-gel is an effective method in producing nanoparticles with high purity and crystallinity. Herein, we report the synthesis of gadolinium oxide nanoparticles (Gd2O3-NPs) via sol-gel technique with an emphasis on the effect of temperature on the crystallization process of the nanoparticles. Gd2O3-NPs were prepared from gadolinium chloride hexahydrate precursor (GdCL3.6H2O) and ethylene glycol (EG). The Gd2O3-NPs were synthesized at different annealing temperatures of 500 °C, 700 °C, 900 °C, 1000 °C and 1100 °C. The X-ray diffraction (XRD) analysis revealed that the sample was crystalline with a cubic phase, achieving optimum crystallinity (82.3%) at an annealing temperature of 1000 °C. The Williamson-Hall (W–H) analysis and size-strain plot (SSP) method demonstrated that the strain decreases with the increment of particle size. Whereby the strain and average particle size of Gd2O3-NPs synthesized at the temperature of 1000 °C were 0.00053 and 62.96 nm respectively. Further investigation by transmission electron microscopy (TEM) indicated that the Gd2O3-NPs is a single-crystal with approximately polycrystalline shapes. The particle size ranges from 38.01 ± 5.9 nm, 49.29 ± 7.41 nm, 60.58 ± 6.7 nm and 74.34 ± 9.3 nm per annealing temperature of 700 °C, 900 °C, 1000 °C and 1100 °C respectively. Whereas, via field emission scanning electron microscopy (FESEM), synthesized Gd2O3-NPs were uniform and had spherical-like morphology with an average diameter of 40.71 ± 4.5 nm, 52.92 ± 6.9 nm, 65.00 ± 7.02 nm and 73.56 ± 10.04 nm at different annealing temperatures of 700 °C, 900 °C, 1000 °C and 1100 °C respectively. The results obtained showed that the mean particle size of the Gd2O3-NPs estimated from the TEM, FESEM, W–H analysis and SSP method were intercorrelated. In terms of molecular conformation, Fourier transform infrared spectroscopy (FTIR) peaks at 448 cm−1 and 546 cm−1 affirms the formation of the Gd2O3-NPs, whereby these peaks corresponds to the Gd–O stretching frequencies of Gd2O3 cubic phase when samples were heated at 700 °C - 1100 °C. It is envisaged that the sol-gel technique is promising in synthesizing Gd2O3-NPs for various possible applications, potentially as a contrast agent for magnetic resonance imaging (MRI).