The ordered phase of methylammonium lead chloride CH3ND3PbCl3 |
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Authors: | Lisheng Chi Ian Swainson Jae-Hyuk Her Osvald Knop |
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Affiliation: | a Chalk River Laboratories, National Research Council of Canada, Neutron Program for Materials Research, Steacie Institute for Molecular Sciences, Building 459, Station 18, Chalk River Laboratories, ON, Canada K0J 1J0 b Department of Physics & Astronomy, State University of New York, Stony Brook, NY 11794-3800, USA c Department of Chemistry, Dalhousie University, Halifax, NS, Canada B3H 4J3 |
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Abstract: | The perovskite-structured compound methylammonium lead chloride orders into a low-temperature phase of space group Pnma, in which at 80 K each of the orthorhombic axes , and is doubled with respect to the room temperature disordered cubic phase (). The structure was solved by ab initio methods using the programs EXPO and FOX. This unusual cell basis for space group Pnma is not that of a standard tilt system. This phase, in which the methylammonium ions, are ordered shows distorted octahedra. The octahedra possess a bond angle variance of 60.663°2 and a quadratic elongation of 1.018, and are more distorted than those in the ordered phase of methylammonium lead bromide. There is also an alternating long and short Pb-Cl bond along a, due to an off-center displacement of Pb within the octahedron. This suggests that the most rigid unit is actually the methylammonium cation, rather than the PbCl6 octahedra, in agreement with existing spectroscopic data. |
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Keywords: | Perovskite Methylammonium lead chloride Phase transition Neutron and synchrotron powder diffraction Rietveld refinement |
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