Investigations on crystalline structure and optical band gap of nearly stoichiometric LiNbO3 nanoparticles

Abstract The structural and optical characteristics of nearly stoichiometric lithium niobate, LiNbO 3 nanoparticles have been studied. The results are very different compared to the bulk LiNbO 3 single crystals. The nanoparticles were synthesized by citrate gel method and the phase was confirmed by powder X-ray diffraction. The size and size distribution of the nanoparticles were obtained by XRD, SEM, TEM and DLS experiments. The particles were in the range of 50–200 nm and most of the particles are about 100 nm of size. The lattice parameters obtained from selected area electron diffraction are a H  = 5.213 A and c H  = 14.026 A for hexagonal system which are slightly larger than the other reported values (JCPDS). The optical properties were obtained from optical absorption spectroscopy in UV–vis.–NIR and IR (FTIR) range, the electronic band gap structure were determined from the fundamental absorption edge in the UV region. The indirect band gap was of 4.78 eV where as the direct gap was of 6.0 eV which are much larger than the other experimental values. The absorption features in the UV range indicate the discrete nature of conduction band and the allowed energy levels in the forbidden gap appeared due to surface defects.