Rietveld crystal structure refinements from high temperature neutron powder diffraction data for the polymorphs of dicalcium silicate

The crystal structures of the γ, α′_L, α′_H, and α forms of dicalcium silicate (C₂S) have been refined by Rietveld analysis of neutron powder diffraction data collected from pure phase material at high temperatures using a heating stage, Two powder refinements of γ-C₂S using data collected before and after the heating run (Bragg R's of 4.65, 2.89%) are of similar quality to previous refinements of single crystal and synchrotron X-ray powder data. The refinement of α′_L-C₂S using data collected at 1060 °C gives a Bragg R of 6.99%, confirming the structure proposed as a result of previous single crystal studies. Data collected at 1250 °C has been refined to a Bragg R of 5.45 % using a disordered α′_H-C₂S structure with all atoms except Si split into two half-occupied mirror-related sites. This result is similar to that obtained in previous Rietveld refinements of synchrotron X-ray powder data. The structure of α-C₂S has been refined to Bragg R of 6.89% using data collected at 1545 °C and a modification of the α-K₂SO₄ structure in which the disordered SiO₄ tetrahedra are oriented slightly away from the c axis.