In situ high temperature single crystal X-ray diffraction study of a natural omphacite

2000 ◽  
Vol 64 (6) ◽  
pp. 983-993 ◽  
Author(s):  
A. Pavese ◽  
R. Bocchio ◽  
G. Ivaldi
Keyword(s):  
High Temperature ◽  
Single Crystal ◽  
Diffusion Processes ◽  
Ambient Conditions ◽  
X Ray Diffraction ◽  
Structural Behaviour ◽  
X Ray ◽  
Thermal Expansion Coefficients ◽  
Using Data

AbstractIn situ high temperature single crystal X-ray diffraction (XRD) experiments have been performed on a chemically quasi-ideal omphacite sample up to 1000°C. The lattice parameters were studied as a function of temperature, and their thermal expansion coefficients determined. The b and c cell edges show discontinuities as a function of temperature which are interpreted here in terms of intracrystalline cation diffusion processes. Structure refinements have been carried out using data collected at room temperature, at 800°C and at ambient conditions after cooling. The structural behaviour as a function of temperature of chemically quasi-ideal omphacites is compared with those of jadeite and diopside.

The low-temperature behaviour of cancrinite:an in situ single-crystal X-ray diffraction study

2012 ◽  
Vol 76 (4) ◽  
pp. 933-948 ◽  
Author(s):  
G. Diego Gatta ◽  
P. Lotti ◽  
V. Kahlenberg ◽  
U. Haefeker
Keyword(s):  
Low Temperature ◽  
Single Crystal ◽  
Structure Refinement ◽  
Ambient Conditions ◽  
X Ray Diffraction ◽  
Structural Behaviour ◽  
X Ray ◽  
Positional Disorder ◽  
Deformation Processes

AbstractThe low-temperature structural behaviour of natural cancrinite with a formula Na6.59Ca0.93[Si6.12Al5.88O24](CO3)1.04F0.41·2H2O has been investigated by means of in situ single-crystal X-ray diffraction and Raman spectroscopy. High quality structure refinements were obtained at 293, 250, 220, 180, 140, 100 and at 293 K again (at the end of the low-T experiments). The variation in the unit-cell volume as a function of temperature (T) exhibits a continuous trend, without any evident thermoelastic anomaly. The thermal expansion coefficient αV = (1/V)∂V/∂T is 3.8(7) × 10–5 K–1 (between 100 and 293 K). The structure refinement based on intensity data collected at ambient conditions after the low-T experiment confirmed that the low-T induced deformation processes are completely reversible. The extraframework population does not show significant variations down to 100 K. The strong positional disorder of the carbonate groups along the c axis persists within the T range investigated. The structural behaviour of cancrinite at low-T is mainly governed by the continuous framework rearrangement through the ditrigonalization of the six-membered rings which lie in a plane perpendicular to [0001], the contraction of the four-membered ring joint units, the decrease of the ring corrugation in the (0001) plane, and the flattening of the cancrinite cages. A list of the principal Raman active modes in ambient conditions is provided and discussed.

Incommensurately modulated ordering of tetrahedral chains in Ca2Fe2O5 at elevated temperatures

2005 ◽  
Vol 61 (6) ◽  
pp. 656-662 ◽  
Author(s):  
Hannes Krüger ◽  
Volker Kahlenberg
Keyword(s):  
High Temperature ◽  
Single Crystal ◽  
Elevated Temperatures ◽  
Three Dimensional ◽  
Ambient Conditions ◽  
X Ray Diffraction ◽  
Modulated Structure ◽  
X Ray ◽  
Left Handed ◽  
Lattice Periodicity

The basic building units of brownmillerite-type A 2 B 2O5 structures are perovskite-like layers of corner-sharing BO6 octahedra and zweier single chains of BO4 tetrahedra. A three-dimensional framework is formed by alternate stacking of octahedral layers and sheets of tetrahedral chains. The compound Ca2Fe2O5 is known to have Pnma symmetry at ambient conditions. The space group Imma was reported to be evident above 963 K. New high-temperature single-crystal X-ray diffraction experiments at 1100 K revealed that Ca2Fe2O5 forms an incommensurately modulated structure adopting the superspace group Imma(00γ)s00, with γ = 0.588 (2). The modulation affects the sequence of the enantiomorphic (right- and left-handed) oriented tetrahedral chains within the layer, breaking the lattice periodicity along c. This ordering can be modelled with crenel occupation modulation functions for the tetrahedrally coordinated Fe, as well as for the O atom interconnecting the tetrahedra.

scholarly journals Crystal structure refinement of MgSiO3high temperature C2/c clinoenstatite

2014 ◽  
Vol 70 (a1) ◽  
pp. C79-C79
Author(s):  
Akira Yoshiasa ◽  
Akihiko Nakatsuka ◽  
Maki Okube ◽  
Tomoo Katsura
Keyword(s):  
High Temperature ◽  
Single Crystal ◽  
Structure Refinement ◽  
Ambient Conditions ◽  
X Ray Diffraction ◽  
Temperature Quenching ◽  
Single Crystal Diffraction ◽  
X Ray ◽  
Metastable Structure ◽  
Rapid Pressure

The high-temperature clinoenstatite (HT-CEn) is one of the important MgSiO3 pyroxene polymorph. The single-crystal of C2/c HT-CEn endmember is firstly synthesized by rapid pressure-temperature quenching from 15-16 GPa and 900-19000C [1]. No report that it is produced as single crystal or large domain has been made on the MgSiO3 endmember. The HT-CEn-type modifications are observed in Ca-poor Mg-Fe clinoenstatite and pigeonite and are always found to be unquenchable in rapid cooling. The high pressure and high temperature experiments of MgSiO3 composition were carried out with a Kawai-type multi-anvil apparatus. The samples were quenched by rapidly releasing the oil pressure load and/or by blow out of anvil cell gasket. The space group of C2/c is strictly determined by Rigaku RAPID Weissenberg photographs and synchrotron radiation. Single-crystal X-ray diffraction experiments were performed at ambient conditions using a Rigaku AFC-5 four circle diffractometer. A total of 9383 reflections was measured and averaged in Laue symmetry 2/m to give 766 independent reflections used for the structure refinements. Final reliability factors converged smoothly to R = 0.029. The single-crystal diffraction analysis shows that the unusual bonding distances frozen in this metastable structure. The degree of kinking of the silicate tetrahedral chains is 1750for HT-CEn. The chain angle for HP-CEn is substantially smaller (1350) and the angle for L-CEn turned to the opposite direction at -1600(=2000). The degree of kinking increases by being curved in more than 1800in the transition from HT-CEn to L-CEn. As for the reverse change from the expansion to the stretch, a potential barrier exists in the point of the continuity. It is suggested that the reason which can quench structure under ambient conditions is the present HT-CEn single crystal was formed by the isosymmetric phase transition from HP-CEn. HT-CEn type single-crystals cannot be frozen without pressure.

High-temperature structural study of decagonal Al–Cu–Rh

2014 ◽  
Vol 70 (2) ◽  
pp. 306-314 ◽  
Author(s):  
Pawel Kuczera ◽  
Janusz Wolny ◽  
Walter Steurer
Keyword(s):  
High Temperature ◽  
Single Crystal ◽  
Structural Study ◽  
Structural Disorder ◽  
X Ray Diffraction ◽  
X Ray ◽  
Decagonal Phase ◽  
Comparative Structure ◽  
The Stability

The structure of decagonal Al–Cu–Rh has been studied as a function of temperature byin-situsingle-crystal X-ray diffraction in order to contribute to the discussion on energy or entropy stabilization of quasicrystals. The experiments were performed at 293, 1223, 1153, 1083 and 1013 K. A common subset of 1460 unique reflections was used for the comparative structure refinements at each temperature. A comparison of the high-temperature datasets suggests that the best quasiperiodic ordering should exist between 1083 and 1153 K. However, neither the refined structures nor the phasonic displacement parameter vary significantly with temperature. This indicates that the phasonic contribution to entropy does not seem to play a major role in the stability of this decagonal phase in contrast to other kinds of structural disorder, which suggests that, in this respect, this decagonal phase would be similar to other complex intermetallic high-temperature phases.

Armstrongite at non-ambient conditions: An in-situ high-pressure single-crystal X-ray diffraction study

2019 ◽  
Vol 274 ◽  
pp. 171-175 ◽  
Author(s):  
Davide Comboni ◽  
Paolo Lotti ◽  
G. Diego Gatta ◽  
Maria Lacalamita ◽  
Ernesto Mesto ◽  
...  
Keyword(s):  
High Pressure ◽  
Single Crystal ◽  
Diffraction Study ◽  
Ambient Conditions ◽  
X Ray Diffraction ◽  
X Ray
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