College Park, Maryland      June 6 - 10 , 2004

WP67: Crystal structure and phase transition of K0.2(NH4)0.8CI mixed salt at low and high temperature

G. Batdemberel (Mongolian University of Science and Technology, Ulaanbaatar, Mongolia; Darmstadt University of Technology, Darmstadt, Germany), A.N. Skomorokhov (Institute for Physics and Power Engineering, Obninsk, Russia; Darmstadt University of Technology, Darmstadt, Germany), L. Smirnov, A.I. Beskrovny (Joint Institute for Nuclear Research, Dubna, Russia), H. Fuess (Darmstadt University of Technology, Darmstadt, Germany), D. Sangaa (National University of Mongolia, Ulaanbaatar, Mongolia), Sh. Chadraabal (Mongolian University of Science and Technology, Ulaanbaatar, Mongolia)

Have been carried out the crystal structure studies of K0.2(NH4)0.8Cl at room temperature by x-ray and neutron diffraction techniques. It was established that the K0.2(NH0.8)Cl compound has CsCI structure with the Pm3m space group. By using of the x-ray powder diffraction determined lattice parameters, K, N, CI atom positions and the thermal factors. From the neutron powder diffraction data determined hydrogen atom position. High-resolution differential calorimetric analysis observed phase transition points at the low temperature T=232K and at the high temperatures T=425K, 458K, 478K, 513K and 573K. On diffractograms obtained at 232K temperature appeared along with CsCI structural reflections the low intensity peaks corresponding to superstructure and if in diffraction data Rietveld refinement procedure to be accounted these superstructure reflections the essential CsCI structure transforms to the tetragonal setting distorted by C3v symmetry. At the high temperature points: 425K, 458K, 478K, 513K and 573K except the CsCI structure peaks have been observed the low intensity diffraction peaks with a monoclinic symmetry and at the point 478K occurred a transition of the CsCI structure to the NaCI structure with Fm3m space group.

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