Mixed alkali effect in the physical and optical properties of xK2O-(25-x)Na2O-12.5MgO-12.5BaO-50B2O3 glasses
2016
Srinivas, G. | Ramesh, B. | Siva Kumar, J. | Shareefuddin, Md | Chary, M.N. | Sayanna, R.
Borate glasses with the composition xK₂O-(25-x)Na₂O-12.5MgO-12.5BaO-50B₂O₃ (x=0, 5, 10, 15, 20 and 25mol%) 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 (ɛ); reflection loss (R); molar refraction (Rₘ); and molar polarizability (αₘ) values of all of the glass samples were evaluated. Rₘ, αₘ and Λₜₕ increase with the increase of the K₂O content. The values of R, ɛ and n increase up to x=10mol% and then decrease above x=10mol%, which may be due to the mixed alkali effect. The density and molar volume values show the opposite behaviour and vary nonlinearly with the K₂O 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.
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