Al-O-Al and Si-O-Si sites in framework aluminosilicate glasses with Si/Al=1: quantification of framework disorder

We present for the first time, direct and clear experimental evidence of Al-O-Al and Si-O-Si linkages in charge-balanced aluminosilicate glasses with Si/Al=1, such as NaAlSiO4 (nepheline) and LiAlSiO4 (beta-eucryptite) compositions using O-17 triple quantum MAS (3QMAS) NMR and quantify the extent of disorder in framework cations (Si/Al). The degree of Al avoidance in NaAlSiO4 glass is 0.942 at 1050 K, and in LiAlSiO4 glass is 0.928 at 930 K (0.902 at 1050 K), which demonstrates the effect of cation field strength on the extent of disorder. In addition, we And a remarkable similarity between the ordering state of the liquid and that of the first, disequilibrium phase to crystallize. (C) 2000 Elsevier Science B.V. All rights reserved.