RAMAN-SCATTERING STUDY OF LITHIUM BORATE GLASSES

Raman spectra of lithium borate glasses in the system xLi2O.(1-x)B2O3 for various values of x (0.10 less-than-or-equal-to x less-than-or-equ al-to 0.50) in the temperature range 25-400-degrees-C are reported. It has been observed that with increasing x, the progressive formation o f pentaborate, tetraborate, diborate, metaborate, pyroborate and ortho borate groups takes place along with the destruction of some of these units. Addition of Li2O to v-B2O3 gives rise to a marked decrease in t he value of the structural correlation range down to approximately 4.2 0 angstrom at the x = 0.50 concentration of Li2O. Thus short-range ord ering in xLi2O.(1-x)B2O3 glasses does not exceed the dimension of one six-membered boroxol ring. The intensity and position of the 130 cm-1 band is not influenced by the addition of lithium oxide. This band pro bably arises due to the librational modes of clusters of B and O atoms . Increasing the temperature of the glass samples results in an increa sing disorder and the consequent thermal expansion of the glass. The i ncrease of the disorder gives rise to an increase in the Raman bandwid th, whereas the thermal expansion of the glass is responsible for the decrease of the frequencies.