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

UNSPECIFIED (2005) Mixed Alkali Effect in $Li_{2}O -Na_{2}O-B_{2}O_{3}$ Glasses Containing CuO-An EPR and Optical Study. In: 50th DAE Solid State Physics Symposium, Dec. 5 - 9, 2005, Bhabha Atomic Research Centre, Mumbai.

 Preview
PDF
PAGE_343_344.pdf

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.