Preparation and characterization of CaO-Al2O3-SiO2 (CAS) glass-ceramics

A glass-ceramic CaO-Al2O3-SiO2 (CAS) system with CaAl2Si2O8 (Anorthite) composition was prepared at two different heat treatment temperatures following the melt-quenching in an arc-melter system. Structural and magnetic properties of the samples were characterized using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and magnetic measurements (M-H, M-T). A clear phase transformation, hexagonal to triclinic, was obtained when heat treatment temperature increased from 930 °C to the 1100 °C. Two different impurity phases were obtained for the sample heat treated at 930 °C, but then these phases dissolved in the main matrix when temperature increased to 1100 °C and single phase CaAl2Si2O8 was obtained. All the samples showed diamagnetic behavior between room temperature and ~ 150 K, but then ferri- or ferromagnetic phase transformation was obtained. This transformation is found to be independent from the heating temperature and believed to be associated with the trapping of free electrons at crystal imperfections and cation ordering between Al and Si in the main matrix.