OH-related infrared absorption bands in oxide glasses

We report the infrared activity, in the spectral region of the OH stretching modes, of different composite silicate glasses whose chemical composition is established by X-ray fluorescence measurements. The analysis of the absorption line profiles is made in terms of different spectral contributions, Gaussian in shape. The comparison with analogous spectra obtained in vitreous silica samples with impurity concentrations <100 part per million moles is evidence of the effects of the different oxides on the vibrational properties of the OH groups. In particular, for oxide glasses a red shift of the composite band at about 3670 cm−1, assigned to the OH stretching modes of free Si–OH groups and of water molecules, is found with respect to those silica samples with the smallest impurity concentrations. Moreover, for oxide glasses the absorption activity in the 2500–3200 cm−1 region shows several spectral contributions that depend on the chemical composition of each sample. Also in view of the fact that in this zone no significant absorption activity is revealed in the case of silica samples, these spectral components are assigned to OH stretching modes of Si–OH groups in interaction with the different atoms present (Na, Ca, K, Al, etc.) and/or in modified sites of the vitreous structure.