Structure refinements of β-Si3N4 at temperatures up to 1360°C by X-ray powder investigation

The structure of β-Si3N4 was reinvestigated with X-ray powder diffraction and Rietveld refinement to determine if the space group should be centrosymmetric, P63/m, or acentric, P63. Displacement for one sort of the nitrogen atoms N(1) away from the high-symmetry positions are found to be even larger than reported before and this behaviour is retained to higher temperatures. R-factor ratio tests favour P63 at a 95% significance level. No exceptional axial thermal expansion was observed. Above 900°C a significant growth of a disordered high-cristobalite phase was observed. It is shown that structure refinements with the X-ray powder technique can be done even at high temperature with high confidence. A newly developed X-ray mirror furnace reaching temperatures up to 1360°C is described.