Disorder in condensed matter systems: proton spin lattice relaxation study of the mixed systems of betaine phosphate and glycine phosphite, $BP_xGPI_{(1-x)}$

Ramanuja, MN and Ramesh, KP and Ramakrishna, J (2007) Disorder in condensed matter systems: proton spin lattice relaxation study of the mixed systems of betaine phosphate and glycine phosphite, $BP_xGPI_{(1-x)}$. In: Magnetic Resonance in Chemistry, 45 (12). 1027 -1034.

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Abstract

Proton NMR relaxation measurements have been carried out in the mixed system of antiferroelectric (AFE) betaine phosphate (BP) and ferroelectric (FE) glycine phosphite (GPI), $BP_xGPI_{(1-x)}$, at 11.4 and 23.3 MHz from 300 to 100 K for x = 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8. The temperature dependence of spin lattice relaxation (SLR) time follows the BPP model in the parent compounds, while the Larmor frequency dependence of T1 in the mixed system is rather unusual. The T1 curve exhibits different slopes for the low-temperature wings at the two frequencies, which is a clear experimental evidence of the presence of different methyl groups with different activation energies $(E_a)$, indicating disorder. For x = 0.3 and 0.4, biexponential recovery of magnetization has been observed below 190 K, showing that the degree of disorder varies with the concentration. The temperature dependence of relaxation time data has been interpreted in terms of $NH_3$, trimethyl ammonium and methyl group reorientations.

Item Type:	Journal Article
Publication:	Magnetic Resonance in Chemistry
Publisher:	John Wiley & Sons
Additional Information:	Copyright of this article belongs to John Wiley & Sons.
Keywords:	Disorder;Mixed system;Betaine phosphate;Glycine phosphite;Proton NMR;Spin lattice relaxation;Distribution of activation energy
Department/Centre:	Division of Physical & Mathematical Sciences > Physics
Date Deposited:	06 Feb 2008
Last Modified:	19 Sep 2010 04:42
URI:	http://eprints.iisc.ac.in/id/eprint/12977

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