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- Title
Microporous crystal structure of labuntsovite‐Fe and high‐pressure behavior up to 23 GPa.
- Authors
Aksenov, Sergey M.; Bykova, Elena A.; Rastsvetaeva, Ramiza K.; Chukanov, Nikita V.; Makarova, Irina P.; Hanfland, Michael; Dubrovinsky, Leonid
- Abstract
Labuntsovite‐Fe, an Fe‐dominant member of the labuntsovite subgroup, was first discovered in the Khibiny alkaline massif on Mt Kukisvumchorr [Khomyakov <italic>et al.</italic> (2001). <italic>Zap. Vseross. Mineral. Oba,</italic><bold>130</bold>, 36–45]. However, no data are published about the crystal structure of this mineral. Labuntsovite‐Fe from a peralkaline pegmatite located on Mt Nyorkpakhk, in the Khibiny alkaline complex, Kola Peninsula, Russia, has been investigated by means of electron microprobe analyses, single‐crystal X‐ray structure refinement, and IR and Raman spectroscopies. Monoclinic unit‐cell parameters of labuntsovite‐Fe are: <italic>a</italic> = 14.2584 (4), <italic>b</italic> = 13.7541 (6), <italic>c</italic> = 7.7770 (2) Å, β = 116.893 (3)°; <italic>V</italic> = 1360.22 (9) Å3; space group <italic>C</italic>2/<italic>m</italic>. The structure was refined to final <italic>R</italic>1 = 0.0467, <italic>wR</italic>2 = 0.0715 for 3202 reflections [<italic>I</italic> > 3σ(<italic>I</italic>)]. The refined crystal chemical formula is (<italic>Z</italic> = 2): Na2K2Ba0.7[(Fe0.5Ti0.1Mg0.05)(H2O)1.3]{[Ti2(Ti1.9Nb0.1)(O,OH)4][Si4O12]2}·4H2O. The high‐pressure <italic>in situ</italic> single‐crystal X‐ray diffraction study of the labuntsovite‐Fe has been carried out in a diamond anvil cell. The labuntsovite‐type structure is stable up to 23 GPa and phase transitions are not observed. Calculations using the BM3 equation of state resulted in the bulk modulus <italic>K</italic> = 72 (2) GPa, <italic>K</italic>′0 = 3.7 (2) and <italic>V</italic>0 = 1363 (2) Å3. Compressing of the heteropolyhedral zeolite‐like framework leads to the deformation of main structural units. Octahedral rods show the gradual increase of distortion and the wave‐like character of rods becomes more distinct. Rod deformations result in the distortion of the silicon–oxygen ring which is not equal in different directions. Structural channels are characterized by a different ellipticity–pressure relationship: the cross‐section of the largest channel I and channel II demonstrates the stability of the geometrical characteristics which practically do not depend on pressure: ϵchannel I ≃ 0.85 (4) (cross‐section is rather regular) and ϵchannel II ≃ 0.52 (2) within the whole pressure range. However, channel III is characterized by the increasing of ellipticity with pressure (ϵ = 0.40 → 0.10).
- Subjects
CRYSTAL structure; ZEOLITES
- Publication
Acta Crystallographica Section B: Structural Science, Crystal Engineering & Materials, 2018, Vol 74, Issue 1, p1
- ISSN
2052-5192
- Publication type
Article
- DOI
10.1107/S205252061700498X