THE INFLUENCE OF WATER OF HYDROLYSIS ON MICROSTRUCTURAL DEVELOPMENT IN SOL-GEL DERIVED LINBO3 THIN-FILMS

The effect of water of hydrolysis on nucleation, crystallization, and microstructural development of sol-gel derived single phase LiNbO3 thi n films has been studied using transmission electron microscopy (TEM), atomic force microscopy (AFM), x-ray diffraction (XRD), and different ial scanning calorimetry (DSC). A precursor solution of double ethoxid es of lithium and niobium in ethanol was used for the preparation of s ol. DSC results indicated that adding water to the solution for hydrol ysis of the double ethoxides lowered the crystallization temperature f rom 500-degrees-C (no water) to 390-degrees-C (2 moles water per mole ethoxide). The amount of water had no effect on the short-range order in amorphous LiNbO3 gels but rendered significant microstructural vari ations for the crystallized films. AFM studies indicated that surface roughness of dip-coated films increased with increasing water of hydro lysis. Films on glass, heat-treated for 1 h at 400-degrees-C, were pol ycrystalline and randomly oriented. Those made with a low water-to-eth oxide ratio had smaller grains and smaller pores than films prepared f rom sols with higher water-to-ethoxide ratios. Annealing films with a low water concentration for longer times or at higher temperatures res ulted in grain growth. Higher temperatures (600-degrees-C) resulted in grain faceting along close-packed planes. Films deposited on c-cut sa pphire made with a 1 : 1 ethoxide-to-water ratio and heat-treated at 4 00-degrees-C were epitactic with the c-axis perpendicular to the film- substrate interface. Films with higher concentrations of water of hydr olysis on sapphire had a preferred orientation but were polycrystallin e. It is postulated that a high amount of water increases the concentr ation of amorphous LiNbO3 building blocks in the sol through hydrolysi s, which subsequently promotes crystallization during heat treatment.