Mixed alkali effect in the physical and optical properties of xK2O-(25-x)Na2O-12.5MgO-12.5BaO-50B2O3 glasses

G. Srinivas, B. Ramesh, J. Siva Kumar, Md. Shareefuddin, M.N. Chary, R. Sayanna
2016 Journal of Taibah University for Science  
Borate glasses with the composition xK 2 O-(25-x)Na 2 O-12.5MgO-12.5BaO-50B 2 O 3 (x = 0, 5, 10, 15, 20 and 25 mol%) were prepared by the melt-quenching technique and were characterized using X-ray diffraction at room temperature. From the optical absorption spectra, the direct forbidden, direct allowed, indirect allowed, and indirect forbidden energy gaps; Urbach energy; refractive index (n); dielectric constant (ε); reflection loss (R); molar refraction (R m ); and molar polarizability (α m )
more » ... larizability (α m ) values of all of the glass samples were evaluated. R m , α m and Λ th increase with the increase of the K 2 O content. The values of R, ε and n increase up to x = 10 mol% and then decrease above x = 10 mol%, which may be due to the mixed alkali effect. The density and molar volume values show the opposite behaviour and vary nonlinearly with the K 2 O content, which manifests the mixed alkali effect in the present glass system. The infrared (IR) spectra of the borate glasses reveal the existence of 3-and 4-coordinated boron atoms. The specific vibrations of the Na-O, K-O, Mg-O, and Ba-O bonds were observed in an IR study.
doi:10.1016/j.jtusci.2015.09.002 fatcat:xpdz2rautnev3pr7o5mgty7z4y