High temperature phase transition of muscovite-2M1: Angle and energy dispersive powder diffraction studies

The `in situ' thermal behaviour of muscovite-2M1 in the range 25-1300 °C has been studied by high temperature X-ray powder diffraction, using both conventional angle-dispersive Bragg-Brentano geometry, and energy-dispersive configuration with synchrotron radiation. The reaction starting at about 850 °C shows a phase transition from muscovite-2M1 to muscovite-1M, which is the precursor of a mullite phase, stable at higher temperatures. The temperature dependence of the lattice parameters is discussed, together with the high temperature structural distortions. The parametrization through the tetrahedra rotation angle indicate a more symmetrical ditrigonal cavity at high temperature. The high temperature diffraction spectra collected in the angle-dispersive mode have been analyzed with the aid of powder profile computer simulation and full-profile multiphase Rietveld refinement.