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.