FAR-INFRARED INVESTIGATION OF THE GENERALIZED LYDDANE-SACHS-TELLER RELATION USING LITHIUM BORATE GLASSES

Far-infrared properties of lithium borate glasses [xLi2O-(1-x)B2O3] we re studied by measuring their reflectivities over a frequency range of 20 approximately 4000 cm-1. The Kramers-Kronig analysis of the measur ed reflectivity in this vibrational spectral region was used to get th e dielectric function, epsilon(omega), of samples with lithium concent rations, x, from 0.0 to 0.4. The ratio of the second moments of Im(-1/ epsilon) and Im(epsilon) was determined. Over the entire lithium conce ntration range, the ratio of the second moments was found to be in goo d agreement with the ratio of epsilon0 and the high-frequency dielectr ic constant epsilon(infinity), as predicted by the generalized Lyddane -Sachs-Teller relation. Moreover, it was experimentally demonstrated t hat a simple relation between the longitudinal, epsilon(l)(omega), and transverse, epsilon(t)(omega), dielectric functions, epsilon(t)(omega )/epsilon(infinity) = 2-epsilon(infinity)/epsilon(t)(omega), is valid for lithium borate glasses.