Identifying and Explaining Vibrational Modes of Sanbornite (Low-Basi2o5) and Ba5Si8O21: A Joint Experimental and Theoretical Study

We report here the analysis of vibrational properties of the sanbornite (low-BaSi2O5) and Ba5Si8O21 using theoretical and experimental approaches, as well as results of high temperature experiments up to 1100-1150 degrees C. The crystal parameters derived from Rietveld refinement and calculations show excellent agreement, within 4%, while the absolute mean difference between the theoretical and experimental results for the IR and Raman vibrational frequencies was <6 cm(-1). The temperature-dependent Raman study renders that both sanbornite and Ba5Si8O21 display specific Ba and Si sites and their Ba-O and Si-O bonds. In the case of the stretching modes assigned to specific Si sites, the frequency dependence on the Si-O bond length exhibited very strong correlations. Both phases showed that for a change of 0.01 angstrom, the vibrational mode shifted 10 +/- 2 cm(-1). These results are promising for using Raman spectroscopy to track in situ reactions under a wide variety of conditions, especially during crystallization. (C) 2020 Elsevier B.V. All rights reserved.