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Proton Dynamics in Letovicite, (NH4)3H(SO4)2: A 1H and 14N NMR Spectroscopic Study

✍ Scribed by Michael Fechtelkord; Astrid Engelhardt; Josef-Christian Buhl; Lutz Schwalowsky; Ulrich Bismayer

Publisher: Elsevier Science
Year: 2000
Tongue: English
Weight: 190 KB
Volume: 17
Category: Article
ISSN: 0926-2040
DOI: 10.1006/snmr.2000.0006

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✦ Synopsis

The improper ferroelastic phase letovicite (NH 4 ) 3 H(SO 4 ) 2 has been studied by 1 H MAS NMR as well as by static 14 N NMR experiments in the temperature range of 296-425 K. The 1 H MAS NMR resonance from ammonium protons can be well distinguished from that of acidic protons. A third resonance appears just below the phase transition temperature which is due to the acidic protons in the paraelastic phase. The lowering of the second moment M 2 for the ammonium protons takes place in the same temperature range as the formation of domain boundaries, while the signals of the acidic protons suffer a line narrowing in the area of T c . The static 14 N NMR spectra confirm the temperature of the motional changes of the ammonium tetrahedra. Two-dimensional 1 H NOESY spectra indicate a chemical exchange between ammonium protons and the acidic protons of the paraphase.

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