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

Abstract

Ba1−xAxTi2O5 (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 Ba1−xCaxTi2O5 spherical glasses suggest that such glasses are suitable for making small optical components.