IR spectra and their application for evaluating physical properties of fluorophosphate glasses

Infrared (IR) absorbance spectra in the range 500–4000cm−1 of the glasses in the system Ba(PO3)2–MgF2–CaF2–AlF3 have been studied with increasing fluoride content. Quantitative justification for assignment of some bands has been attempted. The spectra reveal that the glass structure changes with fluoride addition from metaphosphate, (PO3−)n to P2(O,F)7 and P(O,F)4 along with the formation of Al(O,F)6,[AlF6]3− and [AlF4]−. As a result of these structural changes density (d), refractive index ne) and IR band absorption coefficient at ∼2170 cm−1(αIR) of the glasses vary exhibiting maxima at ∼ 36 mol% fluoride. Statistical analyses show that d and ne are correlated with αIR by linear equations. Each of these equations gives a high correlation coefficient (r) and low residual standard deviation (RSD), and may, thus, be employed for the evaluation of physical properties of fluorophosphate glasses. Physical properties of some fluorophosphate glasses of this work and the published literature have been calculated by using these equations to test their validity. The experimental properties of the glasses present a very good fit of data within 95% confidence interval of the calculated mean values. These facts indicate the suitability of this IR spectroscopic method for the determination of physical properties of fluorophosphate glasses.