Phase transitions in 3,5-dichloropyridine |
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Authors: | F Romain P Tougard B Pasquier N Le Calvé A Novak A Péneau |
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Institution: | 1. Laboratoire de Spectrochimie lnfrarouge et Raman , 2 rue Henri Dunant, 94320, Thiais, France;2. lnstitut d'Electronique Fondamentale , Universite Paris XI , 9 1405, Orsay, (France) |
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Abstract: | Abstract Structural phase transitions in 3,5-dichloropyridine crystal have been studied by calorimetry (150–300 K), X-ray diffraction (300 K), 35Cland 14N nuclear quadrupole resonance (75–300 K) and vibrational spectroscopy (20–300K). Three phases have been shown to exist: phase I, between 338 and 287.5 K, phase 11, between 287.5 and 167.5 K, and phase 111, below 167.5 K. Phase I is characterised by the space group P 2,/m and Z = 2 whereas phases I1 and 111 remain centrosymmetric but double the unit cell. All the phases are ordered and contain crystallo- graphically equivalent molecules. The I ? I1 transition is of first order and probably of the reconstructive type while the II ? III transition is believed to be displacive. Both transitions are monitored by predominantly R′x and R′z librational motions. |
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