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Mixed Alkali Effect in $Li_{2}O -Na_{2}O-B_{2}O_{3}$ Glasses Containing CuO-An EPR and Optical Study
Title:
Mixed Alkali Effect in $Li_{2}O -Na_{2}O-B_{2}O_{3}$ Glasses Containing CuO-An EPR and Optical Study
Archive:
Eprints@iisc
Author(s):
Date:
2005-01-01
Abstract:
The "mixed alkali effect" is one of the classical anomalies of glass science. We report here an interesting phenomenon "Mixed Alkali Effect" observed for a series of $Cu^{2+}$ ions doped $xLi_{2}O-(30-x)Na_{2}O-70B_{2}O_{3}$ (5 leq x leq 25) glasses, investigated by EPR and optical absorption techniques. 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. However, the number of spins participating in resonance (N) and the paramagnetic susceptibility (chi) exhibits the mixed alkali effect. The N is also measured as a function of temperature and the activation energy is evaluated. It is observed that the temperature dependence of paramagnetic susceptibility (chi) obeys Curie-Weiss law. The optical absorption spectra exhibit a strong band corresponding to the transition $(^{2}B_{1g} -> ^{2}B_{2g})$ centered at 13280 $cm^{-1}$. By correlating the EPR and optical absorption data, the molecular orbital coefficients $alpha^{2}$ and $beta^{2}_{2}$ are evaluated. It is interesting to observe that the optical band gap and Urbach energies show the MAE.
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Physics
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Type:
Conference Proceedings
Format:
pdf http://eprints.iisc.ernet.in/archive/00004421/01/PAGE_343_344.pdf
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