INFRARED PROPERTIES OF BARIUM BORATE GLASSES - APPLICATION OF THE GENERALIZED LYDDANE-SACHS-TELLER RELATION

Infrared properties of barium borate glasses, xBaO-(1-x)B2O3, with 0.0 less-than-or-equal-to x less-than-or-equal-to 0.5, have been investig ated. The Kramers-Kronig analysis was used to obtain the complex diele ctric function, epsilon(omega), from the measured reflectivity. As x i ncreases, the infrared active modes around 750 and 1240 cm-1 due to pl anar boroxol rings of B3O6, become weakened. However, new modes appear around 150 and 950 cm-1, which are related to the motions of barium c ations and borate groups containing BO4- tetrahedra, respectively. A s econd moment of Im[epsilon(omega)/epsilon(infinity)], [omega2]t, and t hat of Im[-epsilon(infinity)/epsilon(omega)], [omega2]1, are evaluated . In the entire barium concentration range, [omega2]1/[omega2]t is fou nd to be in good agreement with epsilon0/epsilon(infinity), as predict ed by the generalized Lyddane-Sachs-Teller relation. This result demon strates the usefulness of the second moment representation based on th e Kramers-Kronig relations and associated sum rules.