Abstract
When oxide glasses are modified by dissimilar alkali ions, a maximum in the electric resistivity or the expansion coefficient appears, called the mixed-alkali effect (MAE). This paper reviews the MAE on the thermal, elastic, and vibrational properties of the mixed-cesium lithium borate glasses, x{(1−y)Cs2O-yLi2O}-(1−x)B2O3. For the single-alkali borate glasses, xM2O(1−x)-B2O3 (M = Li, Na, K, Rb, and Cs), the glass transition temperature, Tg = 270 °C, of a borate glass monotonically increases as the alkali content x increases. However, for the mixed-cesium lithium borate glasses the Tg shows the minimum against the lithium fraction y. The dependences of the elastic properties on the lithium fraction y were discussed regarding the longitudinal modulus, Poisson’s ratio, and Cauchy-type relation. The internal vibrational bands related to the boron-oxide structural groups and the splitting of a boson peak were discussed based on Raman scattering spectroscopy. The MAE on various physical properties are discussed on the basis of the changes in the coordination number of the borons and the nonbridging oxygens caused by the dissimilar alkali ions.
Highlights
When oxide glasses are modified by dissimilar alkali ions, a maximum in the electric resistivity or the expansion coefficient appears, called the mixed-alkali effect (MAE)
The alkali ions in a borate glass induce the change of the boron coordination number of a boron atom from three to four and non-bridging oxygens are created as alkali content increases
The modification of oxide glasses by dissimilar alkali ions causes a maximum in the electric resistivity or the expansion coefficient, and that is called the mixed-alkali effect (MAE)
Summary
Crystals and crystalline materials have a three-dimensional periodic structure with translational and point symmetries, their physical properties are anisotropic. The network structure of oxide glasses is remarkably modified by alkali ions, and such a modification has been used to control the various physical properties of glasses such as the glass transition temperatures, elastic properties, etc. Alkali metals remarkably modify the network structure of a borate glass, and the variation in the microscopic structure and related physical properties as a function of the alkali content has been extensively studied. The non-transport physical properties, such as density, glass transition temperature, and elastic modulus, reveal noticeable deviations from the linear variation of the alkali contents. The glass transition temperature, heat capacity, elastic constants, internal Raman bands, and boson peaks show the deviation from the linear relation to lithium fraction These various physical properties are discussed on the basis of the changes of coordination number of boron, creation of non-bridging oxygen, and dissimilar alkali ion pairs
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