Low-temperature crystal structure evolution of (Na,Ca)(Cr,Mg)Si2O6 pyroxene
Research output: Contribution to journal › Journal article › Research › peer-review
The crystal structure of a clinopyroxene with composition (Na0.75Ca0.25)(Cr0.75Mg0.25)Si2O6 was refined at 100, 150, 200, 250 and 298 K. The work was performed in the context of an investigation on the low-temperature behaviour of A+M3+Si2O6 (with A dominant in Na and M = transition elements) pyroxenes in order to provide new insights concerning the phase transition and anomalies recently found in the low-temperature behaviour of NaTiSi2O6 and NaGaSi2O6 compounds. The refinements were done in the C2/c space group (wR2 between 0.048 and 0.068), and no change of symmetry was observed down to 100 K. Highly-anisotropic axial thermal expansion occurs with the scheme
b
a >
c.
UO1 > UT
UM1. Comparison with previous data along the CaMgSi2O-NaCrSi2O6 join suggests significant positional disorder for the O1 oxygen, due to repulsion of the 2p orbitals of O1 and the non-bonding 3d electrons of Cr.
![{alpha}](http://minmag.geoscienceworld.org/math/agr.gif)
![=](http://minmag.geoscienceworld.org/math/ge.gif)
![{alpha}](http://minmag.geoscienceworld.org/math/agr.gif)
![{alpha}](http://minmag.geoscienceworld.org/math/agr.gif)
The M2, M1 and T polyhedra expand with M2 >
M1 >
T, as generally observed in pyroxenes. A discontinuity in the M1 polyhedral volume is observed between 200 and 250 K, similar to the one observed in NaGaSi2O6 between 190 and 235 K.
![=](http://minmag.geoscienceworld.org/math/ge.gif)
![=](http://minmag.geoscienceworld.org/math/ge.gif)
Original language | English |
---|---|
Journal | Mineralogical Magazine |
Volume | 72 |
Issue number | 3 |
Pages (from-to) | 809-816 |
Number of pages | 8 |
ISSN | 0026-461X |
DOIs | |
Publication status | Published - 2008 |
- Faculty of Science
Research areas
ID: 9615921