Fluoroaluminophosphate glasses are promising materials for rare earth dopin
g, but their structure is not yet well known. The structural changes which
take place in the 39AlF(3)-11 NaF-10LiF-(40 - x)(CaF2-MgF2- SrF2-BaF2)-xNaP
O(3) system, with increasing NaPO3 content (0-15 mol%), have been studied b
y polarised Raman and also infrared reflectance spectroscopies. The Raman s
pectra of the glasses, at low-phosphate content, presented a polarised band
peaking near 520 cm(-1), with a shoulder on the high-frequency side, which
was the band with the largest amplitude. This band could be deconvoluted i
nto three Gaussian functions near 515, 570 and 620 cm(-1), assigned to octa
hedral [AIF(6)], five-coordinated [AIF(5)] and tetrahedral [AIF(4)] structu
ral units, respectively. The addition of NaPO3 appeared to promote the form
ation of [AIF(5)] units up to 3 mol% and to increase the conversion of [AIF
(4)] and [AIF(5)] into [AIF(6)] octahedra, beyond 3 mol% of NaPO3. A pictur
e has emerged for the structure of these ionic glasses, in which, for the l
ow-phosphate content, the largest fraction of structural units are [AIF(4)]
tetrahedra, containing both bridging and non-bridging fluorine, some of wh
ich are replaced by [AIF(6)] octahedra, surrounded mostly by nonbridging fl
uorine, as the NaPO3 content increases, bonded to short phosphate chains. (
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