Elastic properties and structure of alkaline-earth silicate glasses

The densities and elastic properties of RO · SiO2 and RO · 2 SiO2 glasses (R = Mg, Ca, Sr, Ba or their mixtures) have been determined to obtain the compositional dependences of volume and bulk modulus of alkaline-earth silicate glasses. The mean atomic volume was found to vary almost linearly with glass composition for a series of RO · SiO2 or RO · 2SiO2 glasses, although there exists a slight negative deviation from the linearity for RO · 2SiO2 glasses when two kinds of alkaline-earth oxides were mixed. The change in glass volume agreed fairly well with the value calculated on the basis of the difference in ionic size of alkali-earth ions being subtituted each other. The bulk moduli of RO · SiO2 and RO · 2SiO2 glasses were found to vary in reciprocal proportion to the four-thirds power of the volume when R was changed from one kind to another, indicating that the difference in internal energy of glass arises mainly from the change in Coulombic attraction due to their size difference. These results seemed to show that the glass structure of a series of RO · 2SiO2 or RO · 2SiO2 glasses remains almost unchanged except the local a change around R ions when R is subtituted from one kind to another.