Structural Dependence of Bulk Modulus of Inorganic Glasses

An attempt to establish some basis for structural interpretation of elastic property of inorganic glasses from the theoretical and empirical relationships between bulk modulus and mean atomic volume of crystalline and glassy materials was reviewed. The relationships were derived on the assumption that the internal energy of a glass changes with the following three causes; (1) the change in Coulombic attraction force due to the ionic size difference of modifying cations or anions being substituted, (2) the change in packing state or coordination number of network forming cations, and (3) the change in excess volume of glassy state. The applicability of the simple atomic theory of elasticity based on Born potential was tested for various oxides and glasses. The inverse four-thirds power dependence of bulk modulus on volume, derivable theoretically for ionic crystals, was found to describe the effect of the first cause for alkali and alkaline earth silicate glasses. The effect of the second cause was examined for the data of polymorphs of SiO,, Ge05 and C, and the inverse fourth power or higher order relationship was es-tablished empirically. The result was applied to interpret the data of alkali germanate and lead borate glasses. The effect of the third cause was discussed by taking the densification of fused silica and the crystallization of lithium silicate glasses as examples. KEY WORDS: Elastic properites / Glass Structure / Equation of state/ I