Variability of optical properties and structure of glass

Abstract

The network theory of glass formation may be broadened by the accessory enhancing effect of some asymmetry of electronic structure to explain the glass formation of compounds containing large amounts of lead oxide. Molar refraction and its variability by cationic environment, temperature and time is used as a measure of electronic displacement. The apparent refraction of oxygen in silicates, borates and phosphates increases with decreasing field strength of cations, with increasing Ο : Si, Ο : Β and Ο : Ρ ratios and with decreasing degree of annealing. The apparent refraction of O2- thus is, for instance, 3.35 in Be2SiO4, 4.97 in Ba2SiO4. In a borosilicate crown annealing may increase density by 1 %, yet decrease refraction by 1/3 %. Generally, in the transformation range a steady, complex ordering phenomenon representable by decreasing entropy takes place which in contrast to discontinuous allotropic changes and in analogy to solid solutions of feldspars corresponds to a continuous series of possible states. In some cases this series may even lead first to denser, then to looser structures during one and the same isothermal treatment. This appears confirmed by experiments on thermal expansion, density and refractive index in different laboratories.