NQR Study of Phase Transition and Cationic Motion in 4-NH2C5H4NHBiBr4·H2O |
| |
Authors: | HARUIO NIKI HIROAKI KINJOU TAICHI FUKUMURA HIROMITSU TERAO MAMI YOSHIDA MASAO HASHIMOTO |
| |
Institution: | (1) Department of Physics, Faculty of Science, University of the Ryukyus, Nishihara Okinawa, 903-0213, Japan;(2) Department of Chemistry, Faculty of Integrated Arts and Sciences, Tokushima University, Minamijosanjima-cho Tokushima, 770-8502, Japan;(3) Department of Chemistry, Faculty of Science, Kobe University, Nadaku Kobe, 657-8501, Japan |
| |
Abstract: | Four 81Br NQR lines in 4-NH2C5H4NHBiBr4·H2O were observed in the temperature range between 77 and ca. 380 K; with increasing temperatures the respective sets of higher
and lower two resonance lines coalesced into single lines discontinuously at 274 K, showing the occurrence of a first-order
type phase transition of this crystal. The transition was confirmed with heat anomaly on a DTA curve. Each higher and lower
line of high-temperature phase is assignable to the terminal Br atoms and the bridging ones of one-dimensional poly anions
(BiBr4
−)
n
in the crystal structure (C2/c), which was investigated by a X-ray structure analysis at room temperature. The 1/T
1 temperature dependence of 81Br NQR follows the usual T
2 law in the temperature range between 77 and ca. 140 K, being explained by fluctuation of the EFG at Br nucleus due to lattice
vibrations. The T
1 vs. 1/T curve in the temperature range between about 160 and 190 K was describable by the exponential curves, allowing us the estimation
of activation energies. These exponential behaviors of T
1 of 81Br NQR are attributable to the fluctuations caused by the thermal motion of 4-NH2C5H4H+ ions. Echo signals of the 81Br NQR could not be detected above 190 K owing to poor S/N with very short T
2. |
| |
Keywords: | 81Br NQR 4-NH2C5H4NHBiBr4·H2O phase transition spin– lattice relaxation times spin– spin relaxation times |
本文献已被 SpringerLink 等数据库收录! |
|