Abstract
Abstract High-pressure neutron diffraction experiments have been performed at room temperature on a powdered sample of the perovskite type-layer compound (CD3ND3)2MnCl4. A phase transition from the orthorhombic room-temperature phase (ORT) to a new high-pressure phase (HP) is demonstrated at 20.5 ± 0.2 kbars. A monoclinic unit cell with lattice parameters a = 6.824 (5) A; b = 7.409 (8) A c = 17.126 (12) A and β = 82.94(9)° has been inferred for the HP phase, consistent with a two-dimensional perovskite-type structure. The HP phase appears to be much more compact than ORT; it is characterized, in particular, by an important compression (≃10%) of the inter-layer distance. Space groups P2/c or P21/c consistent with the experimental data have been deduced for the HP phase, after group theoretical considerations based on shear transformation and order-disorder mechanisms.
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