Effects of reaction temperature on structural properties of ZnO nanocrystals prepared via solochemical technique.

In this research, ZnO nanocrystals were prepared in a few hours by solochemical processing using sodium hydroxide and zinc nitrate hexahydrate as raw materials. Different reaction temperatures have been investigated and revealed their effects on the crystallite size, morphology and crystalline phase of ZnO nanocrystals. Materials synthesized by this technique were investigated employing X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, UV-Visible spectroscopy and Rietveld method. XRD and TEM showed that the ZnO samples are formed by a single hexagonal phase of wurtzite structure containing predominantly rod-like particles, except for the sample obtained at 90 degrees C that is basically formed by rounded nanometric particles. The sample obtained at 90 degrees C presented the smallest average crystallite size (approximately 20 nm) and the highest blue shift between the UV-Vis absorption spectra of the samples when compared to that of ZnO bulk. These size/disorder effects can also explain the attenuation of the ZnO Raman spectrum with increase of reaction temperature.