Powder neutron diffraction study of 2M1 muscovite at room pressure and at 2 GPa

A powder sample of 2M1 muscovite, was studied by time-of-flight neutron diffraction at 1 bar and at 2(\ub1 0.1) GPa. Rietveld refinements of the crystal structure were performed, varying all atomic coordinates in the room-pressure case and only the z coordinates of basal O atoms plus xyz of O and H of the OH group at 2 GPa. In both cases the lattice constants were refined. The unit-cell compression shows deviations from linear elastic behaviour. Inter-layer K-O bonds are compressed along z more than the c lattice constant. The O-H group forms an angle of 85(1)\ub0 with c* and establishes three very loose contacts with neighbouring O atoms. This environment does not change appreciably at 2 GPa. -Author