The structure and properties of glasses and melts in the MgO-Al 2 O 3 -SiO 2 (MAS) and CaO-MgOAl 2 O 3 -SiO 2 (CMAS) systems play an important role in Earth and material sciences. Aluminum has a crucial influence in these systems, and its environment is still questioned. In this paper, we present new results using Raman spectroscopy and 27 Al nuclear magnetic resonance on MAS and CMAS glasses. We propose an Al/Si tetrahedral distribution in the glass network in different Q n species for silicon and essentially in Q 4 and V Al for aluminum. For the CMAS glasses, an increase of V Al and VI Al is clearly visible as a function of the increase of Mg/Ca ratio in the (Ca,Mg) 3 Al 2 Si 3 O 12 (garnet) and (Ca,Mg)AlSi 2 O 8 (anorthite) glass compositions. In the MAS system, the proportion of V Al and VI Al increases with decreasing SiO 2 and, similarly with calcium aluminosilicate glasses, the maximum of V Al is located in the center of the ternary system.

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The solidification process of liquid garnets Ln,A1,0,2 (Ln = Dy, Y, Lu) was probed by differential thermal analysis. A critical temperature r,g was evidenced in the liquid. Cooling from temperatures under rlg leads to the crystallization of the singIe garnet phase. Cooling from temperatures above rlg leads to the solidification of a mixture of perovskite LnAIO, and aluminum oxide a-Al2O3. For Ln = Y, the results are in agreement with stable and metastable phase diagrams previously proposed. The YAIO, melt was shown to display a critical temperature KIP also. Its metastable solidification from temperatures above ZIP leads to the formation of the perovskite at around 1550°C.

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