Structural-relaxation-induced high refractive indices of Ba1−xCaxTi2O5 glasses

Abstract

Ba_1−xA_xTi₂O₅ (A = Mg²⁺, Ca²⁺, or Sr²⁺) spherical glasses were prepared by containerless processing with an aerodynamic levitation furnace. The glass-forming region was x ≤ 0.05 for A = Mg²⁺ and Sr²⁺, but it ranged up to x = 0.90 for A = Ca²⁺. The impact of this exceptionally large amount of Ca²⁺ substituted for Ba²⁺ on the optical properties of high refractive index of BaTi₂O₅ glass was investigated. Although all glasses were colorless and transparent, the optical band gap decreased as the Ca²⁺ content increased. The refractive index increased linearly from 2.10 to 2.18 with increasing Ca²⁺ substitution, while the Abbe number decreased. The optical parameters estimated from the experimental results indicated that Ca²⁺ substitution had a direct impact on the Ti–O bonding state and relaxed the distorted Ti–O polyhedra, which was confirmed by Raman scattering spectra. These results demonstrate that changing the local structure by substituting Ca²⁺ for Ba²⁺ can control the physical properties of high refractive index BaTi₂O₅ glass. The improved physical properties of Ba_1−xCa_xTi₂O₅ spherical glasses suggest that such glasses are suitable for making small optical components.