Mixed Alkali Effect in $Li_{2}O -Na_{2}O-B_{2}O_{3}$ Glasses Containing CuO-An EPR and Optical Study

Chakradhar, Sreekanth RP and Yasoda, B and Rao, Lakshmana J and Gopal, NO (2006) Mixed Alkali Effect in $Li_{2}O -Na_{2}O-B_{2}O_{3}$ Glasses Containing CuO-An EPR and Optical Study. In: Journal of Non-Crystalline Solids, 352 (36-37). pp. 3864-3871.

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Abstract

Electron Paramagnetic Resonance (EPR) and optical absorption spectra of 0.5 mol% CuO doped $xLi_{2}O-(30-x)Na_{2}O-{69.5}B_{2}O_{3}$ (5 \leq x \leq 25) mixed alkali glasses have been investigated. The EPR spectra of all the investigated samples exhibit resonance signals characteristic of $Cu^{2+}$ ions in octahedral sites with tetragonal distortion. It is found that the spin-Hamiltonian parameters do not vary much with x. It is interesting to observe that the number of $Cu^{2+}$ ions participating in resonance (N) and its paramagnetic susceptibility (χ) exhibits the mixed alkali effect with composition. It is observed that the temperature dependence of paramagnetic susceptibility (χ) obeys Curie–Weiss law. The paramagnetic Curie temperature $(\theta_p)$ is negative for the investigated sample, which suggests that the copper ions are antiferromagnetically coupled by negative super exchange interactions at very low temperatures. A broad band corresponding to the transition $(^{2}B_{1g}\longrightarrow^{2}B_{2g})$ in the optical absorption spectrum shows a blue shift with x. By correlating the EPR and optical absorption data, the molecular orbital coefficients $\alpha^{2}$ and $\beta^{2}_{2}$ have been evaluated. It is interesting to observe that the optical band gap $(E_{opt})$ and Urbach energies $(\Delta{E})$ exhibit the mixed alkali effect. The theoretical values of optical basicity $({\Delta}_{th})$ have also been evaluated.

Item Type: Journal Article Copyright of this article belongs to Elsevier. Mixed alkali effect;Absorption;Oxide glasses;Borates; Electron spin resonance Division of Physical & Mathematical Sciences > Physics 10 Oct 2006 19 Sep 2010 04:32 http://eprints.iisc.ernet.in/id/eprint/8820