Radha, K C and Anavekar, R V and Rao, J L and Chakradhar, R P S (2008) EPR and optical studies of Mo(5+) ions in lithium molybdoborate glasses. Applied Magnetic Resonance, 35 (1). pp. 1-13. ISSN 0937-9347

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Abstract

Electron paramagnetic resonance (EPR) and optical absorption studies of Li(2)O-MoO(3)-B(2)O(3) with varying concentrations of Li(2)O, MoO(3) and B(2)O(3) have been carried out at room temperature. Two series of glasses, one with constant MoO(3) (CM) and another with constant borate (CB), have been investigated. Characteristic EPR spectra of Mo(5+) have been observed centered around g congruent to 2.00, which are attributed to Mo(5+) ion in an octahedral coordination sphere with an axial distortion. The spectra also show strong dependence on the concentration of Li(2)O and B(2)O(3). Spin concentrations (N) and magnetic susceptibilities (chi) have been calculated. In the CM series, the N values decrease with increasing Li(2)O content up to 30 mol%, while in the CB series variation of N is found to increase initially up to 20 mol%, and with further increase in Li(2)O content N values tend to decrease. The variation of magnetic susceptibilities is almost similar to that observed with the variation of N. From the optical absorption spectra, and absorption edge (alpha) has been evaluated. In the CM series, the values of alpha show a blueshift. On the other hand, in the CB series a red-shift is observed. The observed variations in spectral parameters are explained by considering the molybdoborate network. Addition of Li(2)O to the CM and CB series results in modification of [MoO(6/2)](0) -> [MoOO(5/2)](-) and [BO(3/2)](0) -> [BO(4/2)](-) -> [BOO(2/2)](-) groups, respectively, leading to creation of nonbridging oxygens. The optical basicity can be used to classify the covalent-to-ionic ratios of the glass, since an increasing optical basicity can be used to classify the covalent-to-ionic ratios of the glass, since an increasing optical basicity can be used to classify the covalent-to-ionic ratios of the glass, since an increasing optical basicity indicates decreasing covalency. It is observed that the covalency between Mo(5+) ions and oxygen ligands increases in the CB series, whereas in the CM series the covalency between Mo(5+) ions and oxygen ligands decreases.

Item Type:	Article
Subjects:	Glass
Divisions:	Glass
Depositing User:	Bula Ghosh
Date Deposited:	20 Jan 2012 05:08
Last Modified:	21 Nov 2012 06:33
URI:	http://cgcri.csircentral.net/id/eprint/400

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