Structural Investigation of Rapidly Quenched Li<sub>2</sub>O-B<sub>2</sub>O<sub>3</sub> Glasses by Raman Spectroscopy

Abstract

Glasses were prepared over a wide range of composition in the system Li2O-B2O3 using a rapid quenching technique. The glass-forming region was extended up to the composition of 70mol% Li2O. Raman spectra of the glasses were measured; drastic spectral changes were observed in the glasses containing more than 50mol% Li2O whereas the spectra of the glasses with the smaller Li2O content showed a close resemblance to each other. The spectra revealed that the main structural units were the six-membered borate rings with BO4 units for the glasses with small Li2O contents and the pyroborate and orthoborate groups for those with large Li2O contents. Corrected Raman spectra were deconvoluted into six Gaussian lines ascribed to specific structural units and the relative amounts of the structural units were determined on the basis of each area of the Gaussian lines. The six-membered borate ring with BO4 units and the pyroborate group were shown to have a maximum proportion at the compositions with 33 and 67mol% Li2O, respectively. A large amount of orthoborate groups, completely discrete anions, was also shown to be present even in the compositions with such a small Li2O content as 25mol%. The fraction N4 of four coordination boron atoms present in the glasses was determined against the glass composition and compared with the results by NMR study. Although in both results a maximum of N4 was observed in the composition region around 30 to 40mol% Li2O, the maximum value in this study was only a half of that by NMR study. This would be caused by the fact that every structural unit was assumed to have the same Raman scattering efficiency.