Molecular Motions and Phase Transitions in Solid CH3NH3PbX3 (X = C1, Br, I) as Studied by NMR and NQR
Open Access
- 1 March 1991
- journal article
- research article
- Published by Walter de Gruyter GmbH in Zeitschrift für Naturforschung A
- Vol. 46 (3) , 240-246
- https://doi.org/10.1515/zna-1991-0305
Abstract
The temperature dependence of 35C1, 81Br, and 127I NQR frequencies and 1Hspin-lattice relaxation times (T1) for CH3NH3PbX3 (X = Cl, Br, I) was measured through the successive phase transitions in these solids. The isotropic reorientation of the CH3NH3 ions takes place in the higher-temperature phases (tetragonal [I4/mcm] and cubic) of the three salts (Ea= 11 kJ mol -1). T1's in the lowest-temperature phases (orthorhombic) indicate that the cations undergo correlated C3-reorientation in the chloride (Ea = 5.45 kJ mol -1)and in the iodide (Ea = 5.80 kJ mol -1, whereas correlated (Ea = 2.40 kJ mol-1) and uncorrected (Ea = 7.50 kJ mol-1) C3- reorientations are excited in the bromide. It is also revealed that the rotational tunneling of the cations governs T1 at lowtemperature region in the orthorhombic phases of these saltsKeywords
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