Vibrational spectra and lattice dynamics of hydrogen-bonded NH4IO3 crystalin the pretransition region

The ferroelectric crystal of ammonium iodate NH4IO3 was investigated by the methods of Raman and IR spectroscopy. Powder IR and Raman temperature depe ndent spectra of the title crystal were measured in the temperature range 3 00-400 K near the Curie temperature (T-c = 367 K). The I-127 nuclear quadru ple resonance (NQR) spectra of the NH4IO3 crystal, which were measured in t he same temperature range, are discussed. The effect of hindered rotation o f NH4+ and IO3- ions was revealed in the pretransition temperature range an d is explained by anomalous crystal thermal expansion. (C) 1999 Elsevier Sc ience B.V. All rights reserved.