NMR Study of Phase Transitions in Betaine Phosphite (CH3)3NCH2COOH·H2PO3

• Published in: Journal of the Physical Society of Japan Vol. 72; no. 9; p. 2250
• Main Authors: Machida, Mitsuo, Ikeda, Hirotaka, Kakiuchi, Takaaki, Ishibashi, Toku, Hasebe, Katsuhiko
• Format: Journal Article
• Language: English
• Published: Tokyo The Physical Society of Japan 01-09-2003
• ISSN: 0031-9015; 1347-4073
• DOI: 10.1143/jpsj.72.2250

The phase transitions in (CH3)3NCH2COOH·H2PO3 at TC1=355 K and at TC2=216 K were studied by nuclear magnetic resonance. Spin-lattice relaxation time T1 of the 13C nucleus in the CH3 group shows two-mode behavior without showing anomaly in the both phase transitions. Activation energies are determined to be 23.1(9) and 1.3(2) kJmol-1 for two modes. T1 of the 13C nucleus in the CH2 group exhibits a shallow dip around TC1, suggesting that the motion of the CH2 group slows down more or less at TC1. T1 of the 31P nucleus takes a minimum at 253 K and activation energy is obtained as 12.6(2) kJmol-1. In addition to the T1 minimum, this shows a sharp dip at TC1 due to the critical slowing-down of the HPO32- motion. The incomplete slow-down of the CH2 motion is considered to be induced by the coupling with the disorder of the HPO32- anion. The critical relaxation rate of the 31P nucleus is well reproduced by the quasi-one-dimensional Ising model. Interaction parameters for intrachain J|| and interchain J[perpendicular] are determined to be 567(1) and 28.4(4) K (J[perpendicular]/J||=0.05), respectively.