Effect of the synthesis route on the structural properties and shape of the indium oxide (In2O3) nano-particles

Nano-crystalline indium oxide (In2O3) particles have been synthesized by sol-gel and hydro-thermal techniques. A simple hydro-alcoholic solution consisting indium nitrate hydrate and citric acid (in sol-gel method) and 1, 4-butandiol (in hydro-thermal method) have been utilized. The structural properties of indium oxide nano-powders annealed at 450 degrees C (for both methods) have been characterized by the X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and specific surface area (SSA) analysis. Structural analysis of the samples shows cubic phase in sol-gel and cubic-hexagonal phase mixture in hydro-thermally prepared particles. The nano-particles prepared by sol-gel method have nearly spherical shape, whereas hydro-thermally-made ones display wire- and needle-like shape in addition to the spherical shape. The obtained In2O3 nano-particles surface areas were 23.2 and 55.3 in sol-gel and hydro-thermal methods, respectively. The optical direct band gap of In2O3 nano-particles were determined to be similar to 4.32 and similar to 4.24 eV for sol-gel and hydro-thermal methods, respectively. These values exhibit similar to 0.5 eV blue shift from that the bulk In2O3 (3.75 eV), which is related to the particle size reduction and approaching the quantum confinement limit of nano-particles. (C) 2009 Elsevier B.V. All rights reserved.