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.

scholarly journals High temperature structural study of decagonal Al-Cu-Rh quasicrystal.

2014 ◽  
Vol 70 (a1) ◽  
pp. C94-C94
Author(s):  
Pawel Kuczera ◽  
Walter Steurer
Keyword(s):  
Structural Changes ◽  
Configurational Entropy ◽  
Lattice Vibrations ◽  
X Ray Diffraction ◽  
Stabilization Mechanism ◽  
X Ray ◽  
Comparative Structure ◽  
The Stability

The structure of d(ecagonal)-Al-Cu-Rh has been studied as a function of temperature by in-situ single-crystal X-ray diffraction in order to contribute to the discussion on energy or entropy stabilization of quasicrystals (QC) [1]. The experiments were performed at 293 K, 1223 K, 1153 K, 1083 K, and 1013 K. A common subset of 1460 unique reflections was used for the comparative structure refinements at each temperature. The results obtained for the HT structure refinements of d-Al-Cu-Rh QC seem to contradict a pure phasonic-entropy-based stabilization mechanism [2] for this QC. The trends observed for the ln func(I(T1 )/I(T2 )) vs.|k⊥ |^2 plots indicate that the best on-average quasiperiodic order exists between 1083 K and 1153 K, however, what that actually means is unclear. It could indicate towards a small phasonic contribution to entropy, but such contribution is not seen in the structure refinements. A rough estimation of the hypothetic phason instability temperature shows that it would be kinetically inaccessible and thus the phase transition to a 12 Å low T structure (at ~800 K) is most likely not phason-driven. Except for the obvious increase in the amplitude of the thermal motion, no other significant structural changes, in particular no sources of additional phason-related configurational entropy, were found. All structures are refined to very similar R-values, which proves that the quality of the refinement at each temperature is the same. This suggests, that concerning the stability factors, some QCs could be similar to other HT complex intermetallic phases. The experimental results clearly show that at least the ~4 Å structure of d-Al-Cu-Rh is a HT phase therefore entropy plays an important role in its stabilisation mechanism lowering the free energy. However, the main source of this entropy is probably not related to phason flips, but rather to lattice vibrations, occupational disorder unrelated to phason flips like split positions along the periodic axis.

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.

scholarly journals A new micro-furnace for 'in situ' high-temperature single-crystal X-ray diffraction measurements

2015 ◽  
Vol 71 (a1) ◽  
pp. s348-s348
Author(s):  
Matteo Alvaro ◽  
Ross J. Angel ◽  
Claudio Marciano ◽  
Sula Milani ◽  
Lorenzo Scandolo ◽  
...  
Keyword(s):  
High Temperature ◽  
Single Crystal ◽  
X Ray Diffraction ◽  
X Ray
Sign in / Sign up

Export Citation Format

Share Document