Evolution of the Ni²⁺ Environment During the Formation of a MgO–Al₂O₃–SiO₂ Glass‐Ceramic: A Combined XRD and Diffuse Reflectance Spectroscopy Approach

Abstract

The effect of the addition of NiO on the crystallization mechanisms has been studied for SiO2–Al2O3–MgO glass‐ceramics. A detailed Rietveld analysis has been made to determine the chemical composition and the cation distribution in the spinel phase and the evolution of Ni2+ coordination site using diffuse reflectance spectroscopy. Powder X‐ray diffraction (XRD) results show the formation of β‐quartz and spinel and the nickel fraction in the spinel phase decreasing as the plateau temperature increases. The determination of cation distribution in spinel using XRD reveals a preference of Ni2+ and Al3+ for octahedral sites and an increasing proportion of Ni2+ in tetrahedral sites for heat treatments at high temperature (1100°C–1200°C). Diffuse reflectance spectroscopy shows that Ni2+ is mainly fivefold coordinated in the starting glass, playing an important role in the crystallization of the spinel phase and it confirms the presence of tetrahedral and octahedral Ni2+ in the glass‐ceramics. The combination of these two techniques also indicates a chemical heterogeneity of spinel crystals with Ni2+‐rich and Mg2+‐rich zones.

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

“…2) are very similar to those previously obtained on Ni-bearing aluminosilicate glasses where Ni 2 þ ions are present mainly in fivefold coordinated trigonal bipyramid sites ( [5] Ni 2 þ characteristic band: 22,700 cm À 1 band) with a small amount of tetrahedral sites ( [4] Ni 2 þ characteristic band: 16,600 cm À 1 band) [10,11,44]. A detailed interpretation of absorption bands can be found elsewhere [6,10].…”

“…5 also show an increase of the bands related to [4] Ni 2 þ and [6] Ni 2 þ due to Ni 2 þ ions entering tetrahedral and octahedral sites in spinel. The final spectrum at 950°C is in agreement with Ni 2 þ in spinel which therefore explains the growth of the [4] Ni 2 þ and [6] Ni 2 þ absorption bands [44].…”

“…Indeed, apart from being a potential optically active ion, Ni 2 þ can influence the crystallization processes [32,[56][57][58]. For instance, NiO in MAS glasses with no nucleating agent can induce spinel formation [44,45], if at least 5 mol% NiO is introduced [32,45]. However these glass-ceramics rapidly loses transparency due to significant crystallization of ß-quartz s.s..…”

“…According to absorption spectra for the MAS-12TiZr-1Ni glass, Ni 2 þ is incorporated in [6] Ni 2 þ sites within spinel at 850°C. In the absence of nucleating agent, the formation of spinel and [6] Ni 2 þ occur at even higher temperatures [44]. Therefore, the addition of TiO 2 (with or without ZrO 2 ) decreases the spinel crystallization temperature.…”

“…The role of these agents was particularly studied in the MgO-Al 2 O 3 -SiO 2 (MAS) ternary system [33][34][35][36][37][38][39][40][41][42][43], in which nucleation and internal bulk crystallization is achieved using TiO 2 and/or ZrO 2 . The MAS glass-ceramics are also well known to promote spinel crystallization [13,44,45]. However, little is known about the interactions between TM and the nucleating agents, which is relevant in order to identify the optimum environment for Ni 2 þ ions that gives a better control of the crystallization processes.…”