The Predictive Power of Electronic Polarizability for Tailoring the Refractivity of High‐Index Glasses: Optical Basicity Versus the Single Oscillator Model

Abstract

High‐density (∼8 g/cm3) heavy metal oxide glasses composed of PbO, Bi2O3, and Ga2O3 were produced, and refractivity parameters (refractive index and density) were computed and measured. Refractive indices were measured at six discrete wavelengths from 0.633 to 10.59 μm using a prism coupler, and data were fitted to the Sellmeier expression. Optical basicity was computed using three models—average electronegativity, ionic‐covalent parameter, and energy gap—and the results were used to compute oxygen polarizability and subsequently the refractive index. Single oscillator energy and dispersion energy were calculated from experimental indices and from oxide energy parameters. The predicted glass index dispersion based on oxide oscillator parameters underestimates the measured index by only 3%–4%. The predicted glass index from optical basicity, based on oxide energy gaps, underpredicts the index at 0.633 μm by only 2%. The calculated glass energy gap based on this optical basicity overpredicts the experimental optical gap by 6%–10%. Thus, we have shown that the density, the refractive index in the visible, and the energy gap can be reasonably predicted using only composition, optical basicity values for the constituent oxides, and partial molar volume coefficients. The relative contributions of the oxides to the total polarizability were assessed, providing an additional insight into controlling the refractivity of high‐index glasses.

Optical Basicity and Nepheline Crystallization in High Alumina Glasses

“…• EM09 glasses: These glasses were high-Al 2 O 3 glasses, whose compositions and crystal fractions were previously reported (McCloy et al 2010). Heat treatments were not CCC, but 950°C for 24 hours.…”

“…There were two exceptions to this requirement. The EM09 data set (McCloy et al 2010) and the SB5-NEPH data set (Fox et al 2007) were included because of their extreme compositions, despite having 24-hour isothermal heat treatments at 950°C. These glasses tended to crystallize large amounts of nepheline or other alkali aluminosilicates, so prove to further limit rather than extend the region of acceptable glass compositions.…”

“…• EM09-Li20m-B-# glasses: Eight new high Li 2 O compositions based on EM09-Li20m-B (McCloy et al 2010) were formulated, fabricated, heat treated, and XRD'd. These glasses are described in this report.…”

“…Several different scales of optical basicities have been proposed which are mutually exclusive (McCloy et al 2010). In general, the OB can be computed for any given glass from the OB of constituents as: (B.1) where q i is the number of oxygen atoms in the i-th component oxide, x i is the i-th component oxide mole fraction, and Λ i is the i-th oxide OB (Mills 1995, Verein-Deutscher-Eisenhuttenleute 1995.…”

“…Thirteen new glasses with a composition similar to HLW-E-Al-24 (denoted PNNL-Al-24-#) were also fabricated and heat-treated. Eight new compositions based on EM09-Li20m- B (McCloy et al 2010) (denoted EM09-Li20m-B-#) and five high Al 2 O 3 glasses (denoted A#) (Hrma et al 2010) were formulated, fabricated, heat-treated. Additional glasses reported to contain nepheline or other NLAS were remade, including some Idaho National Engineering and Environmental Laboratory (INEEL) waste compositions (Riley et al 2001) (DZr-CV-#) and WTP glass HLW-ALG-27 (Vienna and Kim 2008).…”