Magnetic and spectroscopic studies of an iron lithium calcium silicate glass and ceramic

A glass forming matrix consisting of SiO2 - Li2O - CaO was doped with 10% and 15% molar of Fe2O3 and investigated for changes in structural and bulk physical properties of the host when doped with the iron oxide. The vitreous nature of the samples decreases with increase of Fe2O3 from 10 mol% to 15 mol% which is confirmed by the increase in intensity of Bragg's peaks of the XRD patterns and a decrease in the temperature difference between glass transition (Tg) and glass crystallisation (Tc) as found by DTA. Devitrification in this system was achieved by over-doping with Fe rather than heat treatment near Tg. FTIR analysis also reveals that the introduction of Fe ions into the glass matrix causes the anti-symmetric Si-O-Si to shift to lower frequencies on account of the presence of the Fe ions in their modifying structural locations. The optical band gap for all the samples falls in the insulator region. Magnetisation studies of the glass samples show them to be paramagnetic throughout the temperature range of 300 K to 5 K, whereas the glass ceramic sample shows room temperature ferrimagnetism with paramagnetic behaviour at low temperatures attributed to anti-ferromagnetic interactions. Moreover, samples containing iron show a decrease in band gap to almost half of that without iron ions (from 4.05 eV to 2.60 eV) with a further decrease in band gap with increase of iron content. Thus, in principle an increase in Fe content or relative ratios of Fe2 + and Fe3 + as would result from oxygen deficiencies around these ions can be used to achieve desired magnetic and optical properties.