Abstract
Low-frequency Raman spectra of glasses of the types (B 2O 3) 1− x (Li 2O) x , (B 2O 3) 1− x (Rb 2O) x and (B 2O 3) 1 − x − y (Li 2O) x -(Li 2Cl 2) y are presented. The temperature-reduced spectra show a peak at 50 cm −1 and a peak at about 130 cm −1. The peak at 50 cm −1 appears to be a common property of oxide glasses and arises because the limited structural correlation length of the glass network causes a non-zero maximum of the frequency-dependent Raman coupling coefficient. The 130 cm −1 band can be attributed to librational modes of BO 3 and BO 4 units. For v-B 2O 3, a structural correlation length equal to the size of a pair of BO 3 triangles is found. Addition of alkali oxide leads to a decrease of this correlation length. The extra oxygens are mostly incorporated in BO 4 units but larger ions such as Rb + will also enhance the number of non-bridging oxygens. Addition of LiCl does not produce major changes in the Raman spectra and consequently does not change the ratio of the numbers of BO 3 and BO 4 units. The Cl − ions are incorporated in interstitial vacancies of the network, which leads to an expansion of the B-O network structure.
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