Vibrational spectra and lattice dynamics of hydrogen-bonded NH_4IO_3 crystal in the pretransition region

摘要

The ferroelectric crystal of ammonium iodate NH_4IO_3 was investigated by the methods of Raman and IR spectroscopy. Powder IR and Raman temperature dependent spectra of the title crystal were measured in the temperature range 300-400 K near the Curie temperature (T_c = 367 K). The ~(127)I nuclear quadruple resonance (NQR) spectra of the NH_4IO_3 crystal, which were measured in the same temperature range, and discussed. The effect of hindered rotation of NH_4~+ and IO_3~- ions was revealed in the pretransition temperature range and is explained by anomalous crystal thermal expansion.