Structural transformations of Muscovite at high temperature by X-ray and neutron diffraction

Structural transformations of Muscovite at temperature up to 1095 °C were determined using powder X-ray and neutron diffraction. Data were collected at room temperature from preliminary heated and quenched samples at 650 °C, 980 °C and 1095 °C. X-ray data were interpreted by either Rietveld method and neutron data, which complete the structural information by a better assignation of oxygen positions. With neutron data atom position was refined by fitting Pair Distribution Functions. It was found to be a progressive but continuous microstructural change, with the formation of an increasingly disorganized structure, but the layered organization of muscovite is maintained up to 1095 °C. Rietveld refinements from X-ray confirm the 6 to 5 coordination of Al atoms above 650 °C. It induces some structural changes as the orientation and mutual position of tetrahedrons in silicate layers. Pair Distribution Function refinements show the weakening of the long range structural organization, above 5 Å. At lower distance, a local order is maintained and the preferential alignments of both alumina unit pairs and silica tetrahedron were observed. This residual structural order of high-temperature muscovite is favorable to the achievement of textured ceramics.