Low-temperature crystal structure evolution of (Na,Ca)(Cr,Mg)Si2O6 pyroxene
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Low-temperature crystal structure evolution of (Na,Ca)(Cr,Mg)Si2O6 pyroxene. / Nestola, F.; Madsen, Anders Østergaard; Tribaudino, M.; Balic Zunic, Tonci; Ohashi, H.; Secco, L.; Dal Negro, A.
In: Mineralogical Magazine, Vol. 72, No. 3, 2008, p. 809-816.Research output: Contribution to journal › Journal article › Research › peer-review
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TY - JOUR
T1 - Low-temperature crystal structure evolution of (Na,Ca)(Cr,Mg)Si2O6 pyroxene
AU - Nestola, F.
AU - Madsen, Anders Østergaard
AU - Tribaudino, M.
AU - Balic Zunic, Tonci
AU - Ohashi, H.
AU - Secco, L.
AU - Dal Negro, A.
N1 - single-crystal, X-ray diffraction, silicate, low-temperature, clinopyroxene, structure refinements
PY - 2008
Y1 - 2008
N2 - 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. 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. The atomic displacement parameters are scaled according to the following pattern: UM2 > UO2 > UO3 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.
AB - 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. 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. The atomic displacement parameters are scaled according to the following pattern: UM2 > UO2 > UO3 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.
KW - Faculty of Science
U2 - 10.1180/minmag.2008.072.3.809
DO - 10.1180/minmag.2008.072.3.809
M3 - Journal article
VL - 72
SP - 809
EP - 816
JO - Mineralogical Magazine
JF - Mineralogical Magazine
SN - 0026-461X
IS - 3
ER -
ID: 9615921