NEUTRON-SCATTERING FROM AMMONIUM-SALTS .1. COEXISTING PHASES IN NH4I AND NH4+ DYNAMICS IN PHASE-I AND PHASE-II

Neutron quasi-elastic and elastic scattering experiments from NH 4I are reported in the temperature range 213K-300K. It is shown that both while cooling and heating, one obtains an NaCl phase coexisting with low-temperature phases. This calls for great care in interpreting any data on NH4I in this temperature range. The reorientation times for NH 4+ ions in the CsCl phase are determined. In the NaCl phase it is shown that a simple rotational diffusion model does not describe NH4+ reorientations properly.