The modulated structure of synthetic Co-åkermanite, Ca2CoSi2O7

Hagiya, Kenji; Ohmasa, Masaaki; Iishi, Kazuaki

doi:10.1107/s0108768192008048

Cited by 53 publications

(33 citation statements)

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“…The most substantial discrepancy revolves around the SiO~ tetrahedra. In addition to the observed variations in Si207-dimer rotation angles and Si-O1-Si bond angles, Hagiya et al (1993) point out that there are also substantial variations in Si O both lengths that can also account for the splitting of the Si 29 MAS-NMR peaks into three or more subpeaks.…”

Section: Discussionmentioning

confidence: 89%

“…Recently, Hagiya et al (1993) have published a fivedimensional refinement of the Co-~kermanite structure. These authors discuss the changes in the Si-O, Ca-O and Ca-O bond angles and O1-Si-O3 bond angles as a function of the phases of the modulation, s and t. Using the refined modulation functions, the incommensurate structure was calculated (their Fig.…”

Section: Discussionmentioning

confidence: 99%

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Atomic displacements in the normal-incommensurate phase transition in Co-åkermanite (Ca2CoSi2O7)

1994

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Abstract. New in-situ high-temperature X-ray powder diffraction data on the normal-incommensurate phase transition in Co-fikermanite (Ca2CoSi207) are presented. Evidence for the phase transition is found in the abrupt change in the thermal expansivity of the c lattice parameter at 220 ~ C. In addition, the c lattice parameter exhibits premonitory effects of the phase transition through the leveling out of the thermal expansivity at temperatures from 87 to 220 ~ C.The c/a ratio for XzZSi207 incommensurate melilites is shown to be constant for a wide variety of compositions. Correlation of the trends in mean atomic positions with c/a ratio and the sigmoidal variation in the c/a ratio for CazCoSi20 7 provide insight into the atomic displacements occurring in the melilite structure as a function of temperature. Three temperature regimes are discussed in detail (i.e. temperatures well above To, temperatures just above Tc, and temperatures below T~). The atomic displacements occurring in each temperature regime are correlated with the changes in anisotropy and orientation of the atomic displacement ellipsoids for each site, as well as spectroscopic evidence for the increasing number of Z-and T-site environments.

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Section: Discussionmentioning

confidence: 89%

Section: Discussionmentioning

confidence: 99%

Atomic displacements in the normal-incommensurate phase transition in Co-åkermanite (Ca2CoSi2O7)

1994

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“…Moreover, the existence of a low temperature incommensurate phase in åkermanite has been confirmed by electron microscopic and electron diffraction studies (Seifert et al, 1987;Iishi et al, 1989Iishi et al, , 1990 Si MAS NMR (magic angle spinning nuclear magnetic resonance) spectroscopy (Merwin et al, 1989), EXAFS analyses (Tamura et al, 1996), X ray single crystal structure refinement (Kimata and Saito, 1987;Armbruster et al, 1990;Hagiya et al, 1992Hagiya et al, , 1993Kusaka et al, 1998) and other means (cf. Seifert and Röthlisberger, 1993).…”

Section: +mentioning

confidence: 94%

Distribution of Fe3+ in a synthetic (Ca,Na)2(Mg,Fe3+)Si2O7-melilite: 57Fe Mössbauer and X-ray Rietveld studies

Akasaka

Nagashima

Makino

et al. 2005

Journal of Mineralogical and Petrological Sciences

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(T1) and Si(T2) fixed to 0.765, 0.235, 0.515, 0.485 and 2.00, respectively, converged well with an R wp (R weighted pattern) of 13.14% and a goodness of fit of 1.337, indicating exclusive Fe 3+ distribution at the T1 site. However, the Mössbauer spectrum consists of two doublets with an isomer shift of 0.19 mm/s and quadrupole splitting of 0.75 and 1.04 mm/s, which can be attributed to Fe 3+ at the T1 site. There are two sorts of T1 site with distinguishable distortion in the synthetic Na Fe 3+ melilite, which might be attributed to the existence of an incommensurate phase at room temperature.

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“…11). Some synthetic melilite-type compounds with X occupied by calcium and T2 by silicon, with T1 = Mg, Zn, Co, or Fe 2+ , exhibit an incommensurately modulated phase at room temperature (Hemingway et al, 1986;Seifert et al, 1987;Armbruster et al, 1990;Hagiya et al, 1993).…”

Section: (3+2)d Incommensurately Modulated Structure: the Cases Of Mementioning

confidence: 99%

Aperiodic mineral structures

Bindi¹,

Chapuis²

2017

Mineralogical Crystallography

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The modulated structure of synthetic Co-åkermanite, Ca₂CoSi₂O₇

Cited by 53 publications

References 5 publications

Atomic displacements in the normal-incommensurate phase transition in Co-åkermanite (Ca2CoSi2O7)

Atomic displacements in the normal-incommensurate phase transition in Co-åkermanite (Ca2CoSi2O7)

Distribution of Fe<sup>3+</sup> in a synthetic (Ca,Na)<sub>2</sub>(Mg,Fe<sup>3+</sup>)Si<sub>2</sub>O<sub>7</sub>-melilite: <sup>57</sup>Fe Mössbauer and X-ray Rietveld studies

Aperiodic mineral structures

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The modulated structure of synthetic Co-åkermanite, Ca2CoSi2O7

Cited by 53 publications

References 5 publications

Atomic displacements in the normal-incommensurate phase transition in Co-åkermanite (Ca2CoSi2O7)

Atomic displacements in the normal-incommensurate phase transition in Co-åkermanite (Ca2CoSi2O7)

Distribution of Fe<sup>3+</sup> in a synthetic (Ca,Na)<sub>2</sub>(Mg,Fe<sup>3+</sup>)Si<sub>2</sub>O<sub>7</sub>-melilite: <sup>57</sup>Fe M&ouml;ssbauer and X-ray Rietveld studies

Aperiodic mineral structures

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The modulated structure of synthetic Co-åkermanite, Ca₂CoSi₂O₇

Distribution of Fe<sup>3+</sup> in a synthetic (Ca,Na)<sub>2</sub>(Mg,Fe<sup>3+</sup>)Si<sub>2</sub>O<sub>7</sub>-melilite: <sup>57</sup>Fe Mössbauer and X-ray Rietveld studies