Novel binary calcia-alumina systems for device applications

Abstract

The room temperature sol-gel processing technique was employed for the first time in the present work to fabricate the novel binary compound of the calcia-alumina (C12A7) system consisting of calcium oxide (CaO) and aluminium oxide (Al2O3) in a 12:7 ratio. The highest level of homogeneity and transparency of the C12A7 solution in ethanol was achieved by optimizing pH values, reaction dynamics and modified precursor structures. Studies were performed on this binary oxide in both thin film and powder forms. By using High Temperature X-Ray Diffraction (HTXRD) and Simultaneous Thermal Analyzer (STA), phase transformations in C12A7 powder were examined in situ under continuous heat treatment from room temperature to 1200°C. The samples were found to be amorphous at room temperature. As the temperature was increased, crystallisation was completed at 1100°C. The purity of C12A7 and the removal of redundant chemical by-products were confirmed by independent Fourier Transform InfraRed (FTIR) and Raman Spectroscopic measurements. C12A7 thin films were spin coated on single crystal MgO <100> substrates and the effect of heat treatment on crystallinity were investigated using XRD. Initial signs of the crystallisation of C12A7 thin film were observed at 800˚C and the complete crystallisation was achieved on heat treatment at 1100°C for 3 hours. Optical absorption spectroscopy measurements were made in the UV-Visible region and experimental data were analyzed to evaluate the dependence of the band structure of C12A7 crystalline phase on annealing temperature.