Large Amplitude Libration and Structural Phase Transition

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Measurements of ^1H,^2H,^<19>F,^<14>N and ^<127>I NMR and Extended X-ray Absorption Fine Structure (EXAFS) were carried out in several alkylammonium salts and fulleren compounds, in order to clarify the large amplitude vibration, especially librations, and its relation to the structural phase transitions. The temperature dependence of spin-lattice and spin-spin relaxation times and of second moments of NMR linewidth and Debey-Waller factor were determined. The following results were obtained.(1)The local structure of CH_3NH_3I around the I^- ion was studied by iodine K-edge EXAFS in the temperature range of 20-300 K.The crystal structure in the room temperature phase was determined by single crystal X-ray diffraction. The Debye-Waller factor derived from EXAFS shows an anomalous behavior around the order-disorder transition temperature of 166 K.(2)Sn and Br K-edge EXAFS studies were made in (CH_3NH_3)_2SnBr_6 around the phase transition temperature of 149 K.The Debye-walker factor show … More s an anomalous behavior around the temperature.(3)Local structures around Pb (II) and Sn (II) in CH_3NH_3PbX_3 (X=Cl, Br, I) and CH_3NH_3SnX_3 (X=Br、I) were studied by Pb L_<III>-edge and Sn K-edge EXAFS in the temperature range of 10-293 K.The M-X distances (M=Pb, Sn ; X=Cl, Br, I), the coordination numbers, and the Debye-Walker factors were determined in three, four, three, five, and two solid phases of CH_3NH_3PbCl_3, CH_3NH_3PbBr_3, CH_3NH_3PbI_3, CH_3NH_3SnBr_3, and CH_3NH_3SnI_3, respectively.(4)Rb K-edge EXAFS studies on Rb_3C_<60> superconductor were made in the range 6-300 K.The distance (r_<Rb-C>) and Debye-waller factors were found to show the anomalous behavior near T_c.(5)^1H NMR and electrical conductivity of trimethylammonium perchlorate were measured in the ionic plastic phase obtainable above 480 K.In this phase, both cation and anion were revealed to perform self-diffusion. The activation energy of the cationic diffusion was evaluated.(6)^1H,^<19>F,^<14>N and ^<127>I NMR,powder and single crystal X-ray diffraction, differential thermal analysis (DTA) and differential scanning calorimetry (DSC), and electrical conductivity were studied for (CH_3)_3NC_2H_5X (X=I,BF_4) and (CH_3CH_2)_3NHBF_4. Three, five and three solid phases were obtained for (CH_3)_3NC_2H_5I,(CH_3)_3NC_2H_5BF_4 and (CH_3CH_2)_3NHBF_4, respectively. The dynamical behavior of the cation and anion, and its relation to the phase transition were determined. Less