Electron paramagnetic resonance and thermal behaviour of lithium potassium borate glasses containing Cu2+ ions

The structure and thermal behaviour of lithium potassium borate glasses, containing 2 mol% Cu2+ ions, have been studied by means of electron paramagnetic resonance (EPR) and differential scanning calorimetry (DSC). From the observed EPR spectra, the spin-Hamiltonian parameters have been evaluated which are independent of the temperature from room temperature to liquid helium temperature and it is observed that the spin-Hamiltonian parameters (SHP) are dependent on the concentration of alkali ions present in the glass system. The observed SHP shows that Cu2+ ions in lithium potassium borate glasses are present in a distorted octahedral environment. Characteristic glass transition temperatures, T-g, have also been measured for these borate glasses and it is found that the T-g decreases with increasing lithium content upto 10 mol% and then increases for further lithium content. The theoretical optical basicity, Lambda(th,) of the glasses has also been evaluated and it is observed that the changes in optical basicity values are independent of the changes in SHP. (C) 1999 Published by Elsevier Science Inc. All rights reserved.