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Neutron powder diffraction study of the phase transitions in deuterated methylammonium lead iodide.
- Source :
-
Journal of physics. Condensed matter : an Institute of Physics journal [J Phys Condens Matter] 2022 Jan 31; Vol. 34 (14). Date of Electronic Publication: 2022 Jan 31. - Publication Year :
- 2022
-
Abstract
- We report the results of a neutron powder diffraction study of the phase transitions in deuterated methylammonium lead iodide, with a focus on the system of orientational distortions of the framework of PbI <subscript>6</subscript> octahedra. The results are analysed in terms of symmetry-adapted lattice strains and normal mode distortions. The higher-temperature cubic-tetragonal phase transition at 327 K is weakly discontinuous and nearly tricritical. The variations of rotation angles and spontaneous strains with temperature are consistent with a standard Landau theory treatment. The lower-temperature transition to the orthorhombic phase at 165 K is discontinuous, with two systems of octahedral rotations and internal distortions that together can be described by 5 order parameters of different symmetry. In this paper we quantify the various symmetry-breaking distortions and their variation with temperature, together with their relationship to the spontaneous strains, within the formalism of Landau theory. A number of curious results in the low-temperature phase are identified, particularly regarding distortion amplitudes that decrease rather than increase with lowering temperature.<br /> (Creative Commons Attribution license.)
Details
- Language :
- English
- ISSN :
- 1361-648X
- Volume :
- 34
- Issue :
- 14
- Database :
- MEDLINE
- Journal :
- Journal of physics. Condensed matter : an Institute of Physics journal
- Publication Type :
- Academic Journal
- Accession number :
- 35021159
- Full Text :
- https://doi.org/10.1088/1361-648X/ac4aa9