Journal of the Physical Society of Japan · 1990 · 15 citations · 6 references
Natural SciencesMaterials SciencePhysicsCondensed Matter PhysicsCrystal StructureSolid State PhysicsCrystal ChemistryCrystallographyPhase TransitionsSolid-state Phase TransitionsX-ray CrystallographyX-ray DiffractionBrillouin ZonesCritical TemperatureCrystallographic Phase TransitionsDiffuse ScatteringDisplacementTetragonal SystemX-ray Diffraction AnalysisX-ray Diffuse Scattering
The crystal structures of NH 4 SCN are determined in the tetragonal phase I (122°C) and the orthorhombic phase II (100°C, 110°C and 115°C) from X-ray diffraction data. In phase I, SCN - ion is in disordered state taking two equivalent configurations. In phase II, the ordering of SCN - ion correlates to the spontaneous displacement of NH 4 + ion. X-ray critical diffuse scattering is observed at the Z -point of the Brillouin-zone boundary in phase I and critical temperature is determined to be 117°C. The I-II phase transition is explained by a coupling system between the orientational disorder and the phonon.
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