A neutron diffraction and NMR study of the P–T phase diagram of Rb_1-x(NH₄)_xI mixed crystals (x = 0.29,0.77)

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In this Subject: Nuclear Physics ,&nbsp; Physics (General)
By this author: <a href="/search?option2=author&value2=W%3cIMG+SRC%3d%22%2fiso-ents%2fisolat2%2faogon-sgif%22+ALT%3d%22aogon%22%3esicki+J">W sicki J. ;&nbsp; Lewicki S. ;&nbsp; Kozlenko D.P. ;&nbsp; Kozak A. ;&nbsp; Nawrocik W. ;&nbsp; Kichanov S.E. ;&nbsp; Savenko B.N. ;&nbsp; Shchedrina T.

Authors: W aogon sicki J.; Lewicki S.; Kozlenko D.P.; Kozak A.; Nawrocik W.; Kichanov S.E.; Savenko B.N.; Shchedrina T.

Source: Journal of Physics: Condensed Matter, Volume 16, Number 23, 16 June 2004 , pp. 3889-3900(12)

Publisher: IOP Publishing

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Abstract:

The structure of Rb_1-x(NH₄)_xI (x = 0.29,0.77) mixed crystals was studied by means of powder neutron diffraction in the temperature range 20–300 K and at ambient pressure. Measurements of spin–lattice relaxation time T₁ have been performed for polycrystalline samples of Rb_1-x(NH₄)_xI (x = 0.29,0.77) in the temperature range 95–300 K and pressure range 0–800 MPa by the proton NMR technique using the saturation method. Activation parameters were obtained for a model of complex ammonium ion reorientations around two-fold C₂ and three-fold C₃ axes. The activation volume for different phases of the investigated compounds was determined. The experimental data were used for a construction of P–T phase diagram of Rb_1-x(NH₄)_xI (x = 0.29,0.77) mixed crystals. The phase diagram of Rb_0.23(NH₄)_0.77I has similar features to that of NH₄I. Four different phases were found to exist in the temperature and pressure range studied: a disordered agr