Vibrational Spectra of the Ammonia Halides NH₄I and NH₄F
at High Pressures

V. P. Glazkov², D. P. Kozlenko^1, *, B. N. Savenko¹, and V. A. Somenkov²

¹ Joint Institute for Nuclear Research, Dubna, 141980 Russia

² Russian Research Centre Kurchatov Institute, Moscow, 123182 Russia

*e-mail: denk@nf.jinr.ru

Received June 18, 1999

Abstract—The vibrational spectra of ammonium iodide NH₄I at pressures up to 4.1 GPa and ammonium flu-
oride NH₄F at pressures up to 4.7 GPa were investigated by inelastic incoherent neutron scattering. The pressure
dependences of the transverse optical translational and librational modes were obtained. The behavior of the
rotational potential barrier for the ammonium ion as a function of the lattice parameter for disordered and
ordered cubic phases of ammonium halides with CsCl type structure were calculated. The results obtained con-
firm that the transition from an orientationally disordered cubic phase into an ordered cubic phase in ammonium
halides occurs at close critical values of the positional parameter of hydrogen (deuterium). © 2000 MAIK
“Nauka/Interperiodica”.

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