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

Abstract

A glass forming matrix consisting of SiO sub(2)-Li sub(2)O-CaO was doped with 10 percent and 15 percent molar of Fe sub(2)O sub(3) 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 Fe sub(2)O sub(3) from 10 mol percent to 15 mol percent 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 (T sub(g)) and glass crystallisation (T sub(c)) as found by DTA. Devitrification in this system was achieved by over-doping with Fe rather than heat treatment near T sub(g). 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 Fe sup(2+) and Fe sup(3+) as would result from oxygen deficiencies around these ions can be used to achieve desired magnetic and optical properties.