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Influence of cation size on the low-temperature heat capacity of alkaline earth metasilicate glasses

¹ Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, 226-8503 Japan
² Physique des Minéraux et des Magmas, Institut de Physique du Globe, 4 place Jussieu, 75252 Paris cedex 05, France

Correspondence: ^* Permanent address: Physique des Minéraux et des Magmas, Institut de Physique du Globe, 4 place Jussieu, 75252 Paris cedex 05, France. E-mail: richet{at}ipgp.jussieu.fr

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 Sr_0.5Si_0.5O_1.5, Ba_0.5Si_0.5O_1.5, and Mg_0.56Si_0.44O_1.44 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 Mg_1.12Si_0.88O_2.88 is the known glass whose C_P deviates the less from this law.

Key Words: Heat capacity • entropy • alkaline earth silicate glasses