Structure (neutron) of high-temperature phase I potassium iodate at 523 K

The highly disordered crystal structure of triammonium hydrogen disulfate, (NH4)3H(SO4)2, in the high-temperature phase I was studied using single-crystal neutron diffraction. It is known that the O atom involved in hydrogen bonding between neighbouring SO4 tetrahedra is disordered and takes a split-atom position, building a two-dimensional hydrogen-bond network in the (001) plane. The H atoms in these SO4–H—SO4 hydrogen bonds are disordered and hence refined with a split-atom model. Moreover, from the much larger anisotropic mean-square displacements of ammonium protons the NH_4^+ groups were refined with a reasonable split-atom model, and their motional behaviour was also analysed by rigid-body treatment. Finally, careful consideration was given to show possible supplementary proton migration between the ammonium protons and those of the hydrogen bonds in this high-temperature phase.

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Ab initio structure determination of the high-temperature phase of anhydrous caffeine by X-ray powder diffraction

Acta Crystallographica Section B Structural Science ◽

10.1107/s010876810500546x ◽

2005 ◽

Vol 61 (3) ◽

pp. 329-334 ◽

Cited By ~ 39

Author(s):

Patrick Derollez ◽

Natália T. Correia ◽

Florence Danède ◽

Frédéric Capet ◽

Frédéric Affouard ◽

...

Keyword(s):

High Temperature ◽

Phase I ◽

Metastable State ◽

High Temperature Phase ◽

Temperature Phase ◽

X Ray Diffraction ◽

Rietveld Refinements ◽

X Ray ◽

Ab Initio Structure

The high-temperature phase I of anhydrous caffeine was obtained by heating and annealing the purified commercial form II at 450 K. This phase I can be maintained at low temperature in a metastable state. A powder X-ray diffraction pattern was recorded at 278 K with a laboratory diffractometer equipped with an INEL curved position-sensitive detector CPS120. Phase I is dynamically orientationally disordered (the so-called plastic phase). The Rietveld refinements were achieved with rigid-body constraints. It was assumed that on each site, a molecule can adopt three preferential orientations with equal occupation probability. Under a deep undercooling of phase I, below 250 K, the metastable state enters in a glassy crystal state.

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INFLUENCE OF TITANIUM, ZIRCONIUM, AND HAFNIUM ADDITIONS ON THE RESISTANCE OF MODIFIED HASTELLOY N TO IRRADIATION DAMAGE AT HIGH TEMPERATURE: PHASE I.

10.2172/4058614 ◽

1971 ◽

Cited By ~ 2

Author(s):

H. E. McCoy, Jr.

Keyword(s):

High Temperature ◽

Phase I ◽

High Temperature Phase ◽

Irradiation Damage ◽

Temperature Phase ◽

Titanium Zirconium

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Phase Transitions in CsSnCl3 and CsPbBr3 An NMR and NQR Study

Zeitschrift für Naturforschung A ◽

10.1515/zna-1991-0406 ◽

1991 ◽

Vol 46 (4) ◽

pp. 329-336 ◽

Cited By ~ 11

Author(s):

Surendra Sharma ◽

Norbert Weiden ◽

Alarich Weiss

Keyword(s):

Phase Transitions ◽

High Temperature ◽

Phase I ◽

Powder Diffraction ◽

Perovskite Structure ◽

Room Temperature ◽

Monoclinic Phase ◽

High Temperature Phase ◽

Temperature Phase ◽

X Ray

Abstract The phase transitions in CsSnCl3 and CsPbBr3 have been studied by X-ray powder diffraction, by 81Br-NQR and by 'H-, 119Sn-, and 113Cs-NMR. At room temperature in air CsSnCl3 forms a hydrate which can be dehydrated to the monoclinic phase II of CsSnCl3. The high temperature phase I has the Perovskite structure, as the X-ray and NMR experiments show. The three phases of CsPbBr3, known from literature, have been corroborated. The results are discussed in the framework of the group ABX3, A = alkalimetal ion, B = IV main group ion, and X = Halogen ion

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