Zero-Stress Optic Glass without Lead

By comparing data on a variety of examples, an empirical correlation for the photoelastic response of simple metal oxides is discovered and used to predict new families of zero-stress optic glasses. The birefringence induced by uniaxial stress on glass is found to correlate well with the ratio of the metal oxygen bond metallicity to the metal coordination number; the metallicity itself is quantified through the metal oxygen bond length. This correlation was obtained by consideration of the stress optic response of a number of oxide crystals, obtained both from the literature when possible and also from first principles calculations. The correlation obtained provides a simple rule for choosing the composition of oxide glass so as to minimize the stress optic response; this rule is shown to agree with known data on lead oxide glasses and to predict the existence of previously unknown lead-free, zero-stress optic glasses. These glasses were then synthesized, tested, and shown to give the predicted response.