Abstract
Abstract Mössbauer study of potassium germanate glasses containing a small amount of Sn4+ has been performed to know the relationship between the abnormal composition dependence of physical properties, so-called germanate anomaly, and the local structural change of the glasses. Distinct increases in isomer shift and linewidth and a distinct decrease in quadrupole splitting are observed when the concentration of alkali oxide exceeds about 16 mol%. These changes are ascribed to the formation of nonbridging oxygen atoms in GeO4 units. This is also supported by a drastic decrease in a parameter of intermolecular force constant obtained from the temperature dependence of Mössbauer absorption area. The composition dependence of the parameter is well consistent with that of glass transition temperature (Tg) of the same samples. Transformation of GeO4 tetrahedra into GeO6 octahedra is also confirmed by increases in the parameter of intermolecular force constant and in Tg in the alkali content region lower than 16 mol%. The role of Sn4+ is concluded to be a network modifier which is present at an interstitial site of three-dimensional network composed of GeO4 and GeO6 units.
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