Structural and optical properties of (100-x)Li₂B₄O₇·x(Ba₅Li₂Ti₂Nb₈O₃₀) glasses and glass nanocrystal composites.

Optically clear glasses of various compositions in the system (100-x)(Li₂B₄O₇)·x(Ba₅Li₂Ti₂Nb₈O₃₀) (5 ≤ x ≤ 20, in molar ratio) were fabricated by splat quenching technique. Controlled heat-treatment of the as-quenched glasses at 500 °C for 8 h yielded nanocrystallites embedded in the glass matrix. High Resolution Transmission Electron Microscopy (HRTEM) of these samples established the composition of the nano-crystallites to be that of Ba₅Li₂Ti₂Nb₈O₃₀. ¹¹B NMR studies revealed the transformation of BO₄ structural units into BO₃ units owing to the increase in TiO₆ and NbO₆ structural units as the composition of Ba₅Li₂Ti₂Nb₈O₃₀ increased in the glass. This, in turn, resulted in an increase in the density of the glasses. The influence of the nominal composition of the glasses and glass nanocrystal composites on optical band gap (E(opt)), Urbach energy (ΔE), refractive index (n), molar refraction (R(m)), optical polarizability (α(m)) and third order non-linear optical susceptibility (χ³) were studied.