A Single-Crystal Neutron-Diffraction Investigation of Diopside at 10 K

Prencipe, Mauro; Tribaudino, Mario; Pavese, Alessandro; Hoser, A.; Reehuis, M.

doi:10.2113/gscanmin.38.1.183

Cited by 25 publications

(14 citation statements)

References 16 publications

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“…The evolution of the thermal parameters is not linear, as expected for saturation effect approaching 0 K. At 100 K we found a residual thermal motion between 60 and 65% of the roomtemperature value. This value is greater than that found for NaGaSi 2 O 6 at 110 K (50%) (Nestola et al, 2007a), and proportionally greater than that in CaMgSi 2 O 6 at 8 K, which shows a zero point motion from 25 to 35% of the room temperature value (Prencipe et al, 2000). This result may include a slight contribution of structural disorderrelated to the solid solution in the sample studied here, to the quantum effects active at 0 K. A comparison with the room-temperature values of the thermal parameters for NaCrSi 2 O 6 (Ko), CaMgSi 2 O 6 (Di) and Ko 50 Di 50 is instructive.…”

Section: Atomic Displacement Parameterscontrasting

confidence: 58%

Low-temperature crystal structure evolution of (Na,Ca)(Cr,Mg)Si₂O₆ pyroxene

et al. 2008

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The crystal structure of a clinopyroxene with composition (Na 0.75 Ca 0.25 )(Cr 0.75 Mg 0.25 )Si 2 O 6 was refined at 100, 150, 200, 250 and 298 K. The work was performed in the context of an investigation on the lowtemperature behaviour of A + M 3+ Si 2 O 6 (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 NaTiSi 2 O 6 and NaGaSi 2 O 6 compounds. The refinements were done in the C2/c space group (wR 2 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 a b 5 a a > a c .The M2, M1 and T polyhedra expand with a M2 > a M1 > a 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 NaGaSi 2 O 6 between 190 and 235 K.The atomic displacement parameters are scaled according to the following pattern: U M2 > U O2 > U O3 5 U O1 > U T 5 U M1 . Comparison with previous data along the CaMgSi 2 O-NaCrSi 2 O 6 join suggests significant positional disorder for the O1 oxygen, due to repulsion of the 2p orbitals of O1 and the nonbonding 3d electrons of Cr.

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Section: Atomic Displacement Parameterscontrasting

confidence: 58%

Low-temperature crystal structure evolution of (Na,Ca)(Cr,Mg)Si₂O₆ pyroxene

et al. 2008

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“…4. The size of the ADPs is determined by thermal and positional disorder (Prencipe et al, 2000), but also by other experimental uncertainties related to the crystal Ignoring experimental uncertainties and in the absence of non-thermal effects the size of the ADPs is determined by the sum of harmonic and anharmonic contributions, the latter being most significant close to T = 0 K. The result is a quasilinear behaviour at higher temperature, where linear harmonic contributions prevail, which levels off approaching T = 0 K (Willis and Pryor, 1975). Ignoring anharmonic contributions and positional disorder, the ADPs scale linearly through the origin at T = 0 K; a positive intercept may therefore indicate that a positional disorder is present in excess of that from the thermal contribution.…”

Section: Displacement Parameters In Jd 53 Hd 47mentioning

confidence: 99%

Thermal expansion inC2/cpyroxenes: a review and new high-temperature structural data for a pyroxene of composition (Na_0.53Ca_0.47)(Al_0.53Fe_0.47)Si₂O₆(Jd₅₃Hd₄₇)

Tribaudino

Mantovani

2014

Mineral. mag.

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Single-crystal X-ray data collection was performed in situ at T = 300 and 700ºC on a sample synthesized along the jadeite-hedenbergite series. The structural data, together with those of a previous investigation of a crystal of the same composition, were compared to those of the endmembers. The evolution of the displacement parameters with temperature shows significant residuals for the O1, O2 and O3 oxygen at T = 0 K, most significantly in the O1, which were interpreted as an indication of positional disorder.Volume thermal expansion and axial deformation ellipsoids were calculated for the above sample together with those of a series of C2/c pyroxenes. Pyroxenes with a divalent M2 cation, Ca, Fe and Mg have a greater expansion than those with a monovalent M2, like Na and Li; the Na pyroxene endmembers with Al, Cr and Fe were observed to show greater expansion than corresponding Li ones.The greater axial expansion is found along the b axis, except in LiCrSi 2 O 6 ; the changes along the b axis are related to the volume thermal expansion. The axial orientation and anisotropy of the two axes onto the (010) plane is different in Na, Li and Ca-Mg-Fe pyroxenes, but the overall expansion onto the (010) plane, given by the sum of the scalar expansion along the two axes on (010), is very similar in pyroxenes.The deformation along the b axis with temperature and composition is driven by the deformation along b of the octahedral M1 chain; most important is the contribution from the O1ÀO1 shared edge between M1 octahedra in the same octahedral chain.

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“…x, y, z; Àx, Ày, Àz; Ày, xÀy, z; y, Àx+y, Àz; Àx+y, Àx, z; xÀy, x, Àz Ca-O1 2.26 (19) x, y, z+1 Ca-O2 2.662(6) Â 3 y, Àx+y, Àz+1; xÀy+1, x, Àz+1; Àx+1, Ày+1, Àz+1 Ca-O2 2.719(14) Â 6…”

Section: Article In Pressunclassified