Structural evolution of Ni environment in lithium, magnesium and zinc aluminosilicate glasses and glass-ceramics

Three glasses in the Li2O-Al2O3-SiO2 (LAS), MgO-Al2O3-SiO2 (MAS) and ZnO-Al2O3-SiO2 (ZAS) systems were investigated to obtain spinel-based transparent glass-ceramics doped with TiO2 to induce internal nucleation and with NiO to provide optically active ion. The sequence of phase transformations of initial glasses during heat-treatments was studied by in situ X-ray absorption spectroscopy, X-ray diffraction and room temperature optical spectroscopy. For all glasses, there is a change of Ni2+ coordination with the increase of the heat-treatment temperature. The Ni-[5](2+) sites in the parent glass disappear and new distorted Ni-[6](2+) sites are formed within aluminotitanate and (Ni, or Ni,Mg, or Ni,Zn) aluminate amorphous regions. The local environment around Ni2+ then evolves from distorted octahedra to regular octahedra due to the nickel-doped spinel crystallization. In LAS glass-ceramics only, Ni2+ incorporates at elevated temperature octahedral and tetrahedral sites in crystals of beta-quartz solid solution, whose content increases with time and temperature of heat treatment accompanied by a continuous decomposition or dissolution of spinel. In MAS and ZAS glass-ceramics, Ni-doped spinel exist in the whole temperature range of applied heat-treatments. (C) 2015 Elsevier B.V. All rights reserved.