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

[Display omitted] •Experimental and theoretical vibrational modes of sanbornite (low-BaSi2O5) and Ba5Si8O21.•Temperature dependence of the Raman modes.•The experimental results are correlated with first-principle calculations at DFT level. 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