Synthesis and vibrational investigation of lithium magnesium metaborate glasses

Lithium magnesium metaborate glasses xMgO.(1-x)Li2O. B2O3, have been prepar ed by melt quenching in the 0 less than or equal tox less than or equal to1 composition range Their densities and glass transition temperatures exhibi t deviations from additivity (positive and negative respectively). The Four ier transform infrared and Raman spectra of these glasses indicate that in the 0 less than or equal tox less than or equal to0.25 range, Mg2+ has a ve ry small effect on the nature of the local structural units of the glass ne twork. Beyond x approximate to0.25 increasing MgO contents activate the dis proportionation of metaborate species into neutral andpyroborate triangles. As a result the fraction of four coordinated boron atoms, N-4, remains rou ghly constant up to x approximate to0.25 and then decreases, thereby exhibi ting an overall positive deviation fi om additivity. This trend is in marke d contrast to the negative deviation from additivity in NI which is invaria bly observed in mixed mobile ion borate glasses.