The unit-cell parameters and Raman frequencies of Li2SiO3 vary regularly with temperature up to the melting point, which is consistent with the lack of premelting effects in calorimetric measurements. The isostructural lithium (Li2SiO3) and sodium (Na2SiO3) metasilicates have been investigated from room temperature up to the melting point by single-crystal Raman spectroscopy and energy-dispersive X-ray powder diffraction. It is also a possible cause for the anomalous volumetric behavior of potassium silicate glasses. The abundance of three-membered rings in K-silicate melts correlates with a temperature and a non-linear composition dependence of the heat capacity. At a given alkali content, the abundance of these rings increases with increasing cation size. At high alkali content, up to 44% of the SiO4 tetrahedra are part of three-membered rings. A correlation is observed between Tg and the inverse of the entropy of mixing of the different Qn species, which is explained in the framework of the Adam–Gibbs relaxation theory. The chemical shifts and the relative abundance of Qn species correlate with the cationic field strength (Z/r) of the network modifier. Their glass transition temperatures (Tg) were measured by calorimetry. The structure of 21 binary potassium, rubidium and cesium silicate glasses (in the range 15–50 mol% alkali oxide) was analyzed by 29Si single quantum and double quantum MAS NMR spectroscopy.
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