X-ray and neutron investigations of the phase instabilities in K2SnCl6 |
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Authors: | H. Boysen J. Ihringer W. Prandl W. Yelon |
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Affiliation: | Universitätsinstitut für Kristallographie und Mineralogie, 8 München 2, Theresienstr. 41, Germany;Institut Laue-Langevin, B.P. 156, 38042 Grenoble Cédex, France |
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Abstract: | From X-ray and neutron diffraction work with single crystals and powders we found two phase transitions at Tc1 = 260.5 ± 1 K and at Tc2 = 255 ± 1 K. The transition at Tc1 is characterised by the occurence of superstructure reflections breaking the f.c.c. translational symmetry, whereas the second one at Tc2 is indicated by a monoclinic lattice distortion without any further loss of translational symmetry. Both transitions can be explained by the softening of optical branches at the X- and the Γ-point of the Brillouin zone, corresponding to librations of the SnCl6-octahedra. Evidence for this low energy phonon branch is offered from the observation of diffuse streaks with X-rats and from their inelastic nature as revealed by the neutron triple axes technique. |
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