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-equal-to 0.50) in the temperature range 25-400-degrees-C are reported. It has been observed that with increasing x, the progressive formation of pentaborate, tetraborate, diborate, metaborate, pyroborate and orthoborate 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 the value of the structural correlation range down to approximately 4.20 angstrom at the x = 0.50 concentration of Li2O. Thus short-range ordering 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 probably arises due to the librational modes of clusters of B and O atoms. Increasing the temperature of the glass samples results in an increasing disorder and the consequent thermal expansion of the glass. The increase of the disorder gives rise to an increase in the Raman bandwidth, whereas the thermal expansion of the glass is responsible for the decrease of the frequencies.