In situ evolution of Ni environment in magnesium aluminosilicate glasses and glass-ceramics-Influence of ZrO2 and TiO2 nucleating agents

The evolution of Ni2+ environment has been systematically investigated using optical and in situ X-ray absorption spectroscopy (XAS) to determine the influence of nucleating agents (TiO2 and/or ZrO2) during the formation of spinel in magnesium aluminosilicate glass-ceramics. The results were complemented by in situ X-ray diffraction data. According to XAS and optical spectroscopy, the nature of nucleating agents does not modify significantly the Ni environment in initial glasses. However, it has a relatively strong influence in the observed crystallization sequence. Ni2+ ions do not enter the Zr-containing crystalline phase of ZrO2 or ZrTiO4 but a Ni2+ coordination change from the fivefold coordinated sites, with a small amount of tetrahedral sites in parent glasses, to [6]Ni2+ and [4]Ni2+ sites in spinel (in glasses nucleated by ZrO2 and/or TiO2) or in β-quartz solid solutions (in glasses nucleated by ZrO2) has been found.