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

2005 ◽  
Vol 61 (3) ◽  
pp. 329-334 ◽  
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.

scholarly journals High-temperature phase transition of SrRuO3and SrHfO5: X-ray diffraction and PAC spectroscopy

1996 ◽  
Vol 52 (a1) ◽  
pp. C364-C364
Author(s):  
J. A. Guevara ◽  
S. L. Cuffini ◽  
Y. P. Mascarenhas ◽  
P. de la Presa ◽  
A. Ayala ◽  
...  
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Pac Spectroscopy ◽  
X Ray Diffraction ◽  
X Ray ◽  
Temperature Phase Transition

scholarly journals Study of the High Temperature Phase of 1,16-Hexadecanediol by Polarized Light Microscopy and Glancing Incidence X-Ray Diffraction

2018 ◽  
Vol 24 (S1) ◽  
pp. 2248-2249
Author(s):  
M. Ramírez-Cardona ◽  
M.P. Falcón-León ◽  
G. Luis-Raya ◽  
G. Mejía-Hernández ◽  
R. Arceo ◽  
...  
Keyword(s):  
High Temperature ◽  
Light Microscopy ◽  
Polarized Light ◽  
High Temperature Phase ◽  
Polarized Light Microscopy ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
X Ray

Revision of the Li–Si Phase Diagram: Discovery and Single-Crystal X-ray Structure Determination of the High-Temperature Phase Li4.11Si

2013 ◽  
Vol 25 (22) ◽  
pp. 4623-4632 ◽  
Author(s):  
Michael Zeilinger ◽  
Iryna M. Kurylyshyn ◽  
Ulrich Häussermann ◽  
Thomas F. Fässler
Keyword(s):  
Phase Diagram ◽  
High Temperature ◽  
Single Crystal ◽  
Structure Determination ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
X Ray

From six- to five-coordinated SbIII in [(CH3)3PH]3[Sb2Cl9]: transition pathways from single-crystal X-ray diffraction

2008 ◽  
Vol 64 (5) ◽  
pp. 558-566 ◽  
Author(s):  
Anna Gagor ◽  
Maciej Wojtaś ◽  
Adam Pietraszko ◽  
Ryszard Jakubas
Keyword(s):  
Phase Transitions ◽  
Phase I ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Octahedral Environment ◽  
Transition Pathways ◽  
Cl Atoms ◽  
Unusual Increase

[(CH3)3PH]3[Sb2Cl9] experiences four phase transitions which were found by means of calorimetry, thermogravimetry and X-ray diffraction. The crystal structure was solved in the space group P63/mmc at 382 K (phase I), Pnam at 295 K (phase II) and Pna21 at 175 K (phase V). We observed an unusual increase in symmetry from the monoclinic to the orthorhombic form at the IV\rightarrowV transition. The parent hexagonal high-temperature phase I consists of highly disordered [(CH3)3PH]+ cations and [Sb2Cl9]3− anions with an octahedral environment of SbIII. The transition from phases I to II is associated with the ordering of [(CH3)3PH]+ cations. Moreover, the successive transformations from phases I to V are related to the change in the arrangement of Cl atoms in [Sb2Cl9]3− anions from the discrete `face-sharing bioctahedra' (phase I) to two corner-sharing square pyramids. A mechanism for the phase transitions is proposed. It is observed that weak C—H...Cl interactions are responsible for the structure arrangement in low-temperature phases.

Investigation on the Thermal Stability of the Compounds Y3Fe29-xCrx

2013 ◽  
Vol 820 ◽  
pp. 71-74
Author(s):  
Xiao Hua Wang ◽  
Wei He ◽  
Ling Min Zeng
Keyword(s):  
Thermal Stability ◽  
High Temperature ◽  
Single Phase ◽  
Binary Compound ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Transition Elements ◽  
X Ray Diffraction ◽  
X Ray ◽  
Thermal Stability Of

Binary compound Y3Fe29cannot be directly formed by rare earth Y and Fe and the third element M (non-iron transition elements) must be introduced to form ternary compound Y3(Fe,M)29. In this work, six alloys with compositions of the Y3Fe29-xCrx(x=1,2,3,4,5,6) were prepared and investigated by X-ray diffraction (XRD), Scanning electron microscopy (SEM) and differential thermal analysis (DTA). The study on the thermal stability of these compounds points to that the compoundY3(Fe,Cr)29is a high temperature phase and exists above 1100K. The alloys with single-phase of Y3(Fe,Cr)29was decomposed into Y2(Fe,Cr)17and Y(Fe,Cr)12annealed at high temperature 1100K.

Synthesis, Thermal and X-Ray Investigations of the High-Temperature Phase of Copper(I) Cyanide

2003 ◽  
Vol 58 (1) ◽  
pp. 155-158 ◽  
Author(s):  
Olaf Reckeweg ◽  
Cora Lind ◽  
Arndt Simon ◽  
J. Salvo
Keyword(s):  
High Temperature ◽  
Ir Spectroscopy ◽  
Chemical Analysis ◽  
Rietveld Refinement ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
X Ray

Abstract CuCN was investigated by chemical analysis, IR spectroscopy and powder X-ray diffraction. A high-temperature phase of CuCN was identified and structurally characterized by Rietveld refinement. HT-CuCN is isotypic to AgCN (R3m (No. 166), Z = 3, a = 597.109(8), c = 484.33(5) pm, Cu (3a), C/N (6c), z = 0.3915(10) at 77 K) with head-tail disorder of the cyanide anions.

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