T HE INFLUENCE of compositional variations on the physical properties such as, density, molar volume, ,molar refraction, optical energy gap, refractive index , optical basicity, oxide ion polarizability, metallization, and third order nonlinear susceptibility, nonlinear refractive index, with the variation in Nb 2 O 5 content has been studied theoretically for glasses of compositions xNb 2 O 5 (20-x)BaO80TeO 2 (x=0, 5, 10,15) and the physical parameters related to these compositions were analyzed with theoretical predictions.The density calculated decreases with the increase of Nb 2 O 5 content from 5.680 g cm -3 to 5.493 g cm -3 , this means that the glass matrix becomes less dense. It was found that , the optical energy gap decreases, but the refractive index increases by increasing Nb 2 O 5 content.The electronic polarizability of oxide ion decreases with decreasing the optical basicity. The value of optical basicity shows that the glass materials are less basic. It is suggested that by increasing Nb 2 O 5 content ,the glasses become less polarized. Also, It was found that the values of third order nonlinear susceptibility increases by increasing Nb 2 O 5 content and are found to be larger than those of the silica based glasses. The glasses are found to possess a high refractive index (2.170-2.213), a comparatively narrow band gap (3.992eV-3.785eV), high electronic ion polarizability (2.445 Å 3 -2.546 Å 3 ) and high optical basicity (0.987-1.014). It was found that the values of the third order nonlinear optical susceptibility are in the range (0.7604-0.9271)x10 -12 esu. Finally, all the above values are a good basis for predicting new non linear optical materials.

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T HE OPTICAL and electrical properties of xSb 2 O 3 (35-x) B 2 O 3 60Bi 2 O 3 5TeO 2 glass system (where, x=10, 20, 30) have been studied. It was found that the values of optical energy gap and activation energy of conduction decrease by increasing Sb 2 O 3 content for all the studied samples .While as the values of refractive index, real dielectric constant ,molar polarizability ,oxide ion polarizability, optical basicity, third order nonlinear optical susceptibility increase by increasing Sb 2 O 3 content. The high values of third order nonlinear optical susceptibility for all the studied samples , were found to be in the range (3.827-8.219) x 10 -12 esu, which is larger than that of pure silica glass.Finally, it has been suggested that all the studied samples are promising materials for nonlinear optical requests.