| | 1 | Author
| Masao Hashimoto, Akiko Shono, Yoshiyuki Mido, Haruo Niki, Hiroshi Hentona, Koichi Mano | Requires cookie* | | | Title
| Narrowing of the 3 5 CI NQR Lines of Trichloroacetamide Caused by Its Ferroelectric Phase Transition  | | | | Abstract
| Dielectric measurements on single crystals and DSC of the title compound (monoclinic, space group P2 X) revealed a ferroelectric transition at ca. 355 K (AH xs 0.5 kJ mol"Powder x-ray diffraction indicated that the high temperature phase is also monoclinic and the change in volume at the transition is very small. A displacement of hydrogen atoms is considered as responsible for the appearance of ferroelectricity. The 35 C1 NQR signals at ca. 77 K were considerably broad, but a drastic narrowing took place after the compound had once experienced the phase transition. A tentative assignment of the NQR spectrum was made from a calculation of the NQR frequencies based on the CNDO/2 method. Another phase transition was evidenced by a small drift of the DSC curve and a slight anomaly of the dielectric behavior around 358 K. The present *H NMR experi-ments gave no indication of the onset of torsional motion of the NH 2 group reported to occur at ca. 210 K. | | | |
Reference
| Z. Naturforsch. 45a, 327—333 (1990); received August 26 1989 in revised form November 1 1989 | | | |
Published
| 1990 | | | |
Keywords
| NQR, Phase transition, Ferroelectricity, Hydrogen bond, Disordered structure | | | |
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| default:Reihe_A/45/ZNA-1990-45a-0327.pdf | | | | Identifier
| ZNA-1990-45a-0327 | | | | Volume
| 45 | |
| 2 | Author
| Masao Hashimoto, Takahiro Isono, Haruo Niki, Takuya Higa | Requires cookie* | | | Title
| Fade-Out of 35 C1 NQR in Chloral n-Butylhemiacetal | | | | Abstract
| Continuous wave and pulsed NQR, dielectric absorption and infrared (IR) measurements were carried out to investigate the origin of the peculiar temperature dependence of the S/N ratio of the 35 C1 NQR in the title compound. The dielectric and IR experiments evidenced a thermally activated jumping motion of the H atom participating in O-H O H-bonds. As T x and T 2 below 120 K were much longer than T 2 * of about 10 us, the line broadening in this temperature region was attributed to static lattice defects. A random freezing of the jumping motion may be the origin of the defects. In the range 120-170 K, S/N was extremely low and T 2 was less than 10 |is, probably having a minimum in between. The short T 2 is considered to be responsible for the low S/N. A minimum of S/N at about 240 K is attributed to a 7\ minimum (less than 10 (is) at that temperature. | | | |
Reference
| Z. Naturforsch. 45a, 472—476 (1990); received August 26 1989 in revised form December 1 1989 | | | |
Published
| 1990 | | | |
Keywords
| NQR, Relaxation times, Hydrogen bond, Dielectric absorption, Disordered structure | | | |
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| default:Reihe_A/45/ZNA-1990-45a-0472.pdf | | | | Identifier
| ZNA-1990-45a-0472 | | | | Volume
| 45 | |
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