Identifying and explaining vibrational modes of sanbornite (low-BaSi2O5) and Ba5Si8O21: A joint experimental and theoretical study

Abstract

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 °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 BaO and SiO bonds. In the case of the stretching modes assigned to specific Si sites, the frequency dependence on the SiO bond length exhibited very strong correlations. Both phases showed that for a change of 0.01 Å, 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.