NMR study of phase transitions in new ferroelectric Crystal--(C5H5NH)5Bi2Br11.
A T1 minimum at 216 K for Larmor frequency 90 MHz has been detected and for this minimum no analogous T, minimum according to the known quadratic dependence of the Larmor frequency 25 MHz is found. The analysis leads to the conclusion that this T1 minimum is a result of the relaxation of protons via quadrupole nuclei. The Kimmich theoretical treatment of 1H NMR experiments exhibiting the existence of this phenomenon in the case of relaxation of protons of piridinium cations in (C5H5NH)5Bi2Br11 and the estimated averaged quadrupole frequency of interacting quadrupole nuclei has been estimated to be around 71 MHz. Below the phase transition at 118 K a wide symmetric spin-lattice relaxation minimum at 25 MHz is detected and a model of small angle libration of the pyridinium cation has been applied to explain the observed T1 relaxation time minimum.
Medycki
Wojciech
W
Institute of Molecular Physics, PAS, Poznań, Poland.
Jakubas
Ryszard
R
D009682:Magnetic Resonance Spectroscopy; D011726:Pyridinium Compounds
D011726:Pyridinium Compounds