- © 2009 American Mineralogist
The heat capacities of Sr and Ba metasilicate glasses and of a Mg silicate glass with only 44 mol% SiO2 have been measured between 2 and 300 K with the Quantum Design Physical Property Measurement System. The derived vibrational entropies S298-S0 are 50.90, 61.00, and 36.65 J/(mol · K) for Sr0.5Si0.5O1.5, Ba0.5Si0.5O1.5, and Mg0.56Si0.44O1.44 glasses, respectively. Along with available data for Mg- and Ca-bearing glasses, these results indicate a regular variation of the partial molar vibrational entropy of the metal oxide as a function of the ionization potential of the cation. At very low temperatures, however, the excess heat capacity of barium metasilicate glass relative to Debye limiting T3 law is stronger than expected from such a trend, whereas Mg1.12Si0.88O2.88 is the known glass whose CP deviates the less from this law.