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By combining data from oxide melt solution calorimetry and  29 Si MAS-NMR spectroscopy, the enthalpy for short-range Si,Al ordering in b-eucryptite (LiAlSiO 4 ) was determined for a series of samples prepared by glass annealing. Si,Al ordered b-eucryptite gives a single  29 Si NMR peak for two unresolved crystallographic sites, but two distinct  27 Al resonances that differ in both chemical shift and quadrupolar coupling. Samples of β-eucryptite crystallized from glass contain additional  29 Si NMR peaks, indicating significant levels of short-range Si,Al disorder. This disorder decreases exponentially with annealing time at 1173 K, from 0.55(±0.04) Al-O-Al linkages per formula unit after one hour to 0.05(±0.01) after 70.5 hours. The decrease in the concentration of Al-O-Al linkages with annealing time correlates linearly with enthalpies of drop-solution in molten lead borate, giving an enthalpy of ΔH ord  = -26 ± 3 kJ/mol for the reaction: Al-O-Al + Si-O-Si → 2(Si-O-Al).

29 Si and 27 Al MAS-NMR spectroscopy of b-eucryptite (LiAlSiO4): The enthalpy of Si,Al ordering