Phase transformations in NiO and CoO doped magnesium aluminosilicate glasses nucleated by ZrO2

Abstract

Phase transformations and formation of transparent colourless and coloured glass ceramics in a model magnesium aluminosilicate glass nucleated by ZrO 2 and/or doped by NiO or CoO were studied using small angle x-ray scattering (SAXS), x-ray diffraction analysis (XRD), optical and Raman spectroscopy. In the initial glasses Ni(II) and Co(II) ions are predominantly octahedrally coordinated. According to XRD and Raman spectroscopy data, in the course of heat treatment at the nucleation stage, tetragonal ZrO 2 nanosized crystals precipitate preceded by the formation of ZrO 2 embryos. According to the SAXS data, interference effects caused by the regularity of the ZrO 2 distribution in the glassy matrix leads to decreased light scattering and ensures transparency of the glass ceramic materials. At this stage, Ni(II) and Co(II) ions remain in the residual glass phase. After heat treatments at elevated temperatures, Mg-petalite, β-quartz solid solution and spinel precipitate. Absorption spectra of the material change due to Ni (II) and Co(II) ions entering the aluminosilicate crystalline phases. Upon crystallisation of the main phase, a bimodal distribution of ZrO 2 crystals develops. Large sized crystals of ZrO 2 are irregularly dispersed. Sizes of the ZrO 2 nanocrystals estimated by SAXS, XRD analysis and low frequency Raman spectra are in a good agreement.