STRUCTURE, THERMAL PROPERTIES AND MIXED ALKALI EFFECT IN Li2O AND Na2O DOPED BORATE GLASSES

The thermal and structural properties of melt-quenched Li2O and Na2O doped borate glasses were investigated. The non-crystalline nature of the as-quenched samples has been established by XRD studies. The structural and thermal properties of the present glasses have been studied using Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). The formation of both BO3 and BO4 units in the studied samples has been ascertained by the FTIR studies. The nonlinear variation of peak positions of B-O bonds of stretching vibrations validate the occurrence of mixed alkali effect. The glass transition temperature (Tg) and thermal stability (∆t) exhibited a non-linear variation with increase in (Li2O+Na2O) content. With increasing the concentration of dopants, the Tg and ∆t respectively exhibited maxima and minima at x=0.30. This kind of behavior has been attributed to the structural modifications occurring in the network as a function of compositional variation. This is considered to be the signature for a possible mixed alkali effect taking place in the present glass systems.