Raman scattering study of BaF 2 ZrF 4 FeF 2 glasses

Several BaF 2 ZrF 4 glasses containing 5 mol% FeF 2 have been studied to elucidate the fraction of nonbridging fluorine atoms (−F − ) in a ZrF 6 octahedron constituting a zigzag chain. A continuous increase in the fraction of nonbridging fluorine atom in a ZrF 6 octahedron is deduced from the increase in the integrated peak intensity of the symmetric stretching-vibrational mode ( ν s ) for the Zr-nonbridging fluorine atom when the BaF 2 (+ FeF 2 ) content is lower than 38 mol%, i.e., in the composition region where the average coordination number of Zr is regarded as six. This result is well consistent with the previous results obtained from Raman studies of binary BaF 2 HfF 4 glasses, and also with those of Mössbauer and Raman studies of ternary BaF 2 ZrF 4 FeF 2 glasses. A drastic decrease in the symmetric-stretching vibrational mode ( ν s ) in 42BaF 2 ·53ZrF 4 ·5FeF 2 glass suggests that a friction of ZrF 6 octahedron is reduced when BaF 2 (+FeF 2 ) content is close to 50 mol%. The zigzag chain is therefore considered to be constituted of ZrF 7 units in such glasses.