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Microporous crystal structure of labuntsovite‐Fe and high‐pressure behavior up to 23 GPa
Author(s) -
Aksenov Sergey M.,
Bykova Elena A.,
Rastsvetaeva Ramiza K.,
Chukanov Nikita V.,
Makarova Irina P.,
Hanfland Michael,
Dubrovinsky Leonid
Publication year - 2018
Publication title -
acta crystallographica section b
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.604
H-Index - 33
ISSN - 2052-5206
DOI - 10.1107/s205252061700498x
Subject(s) - crystallography , monoclinic crystal system , crystal structure , electron microprobe , bulk modulus , materials science , diamond anvil cell , raman spectroscopy , x ray crystallography , crystal (programming language) , empa , chemistry , analytical chemistry (journal) , mineralogy , diffraction , physics , chromatography , optics , programming language , computer science , composite material
Labuntsovite‐Fe, an Fe‐dominant member of the labuntsovite subgroup, was first discovered in the Khibiny alkaline massif on Mt Kukisvumchorr [Khomyakov et al. (2001). Zap. Vseross. Mineral. Oba, 130 , 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: a = 14.2584 (4), b = 13.7541 (6), c = 7.7770 (2) Å, β = 116.893 (3)°; V = 1360.22 (9) Å 3 ; space group C 2/ m . The structure was refined to final R 1 = 0.0467, wR 2 = 0.0715 for 3202 reflections [ I > 3σ( I )]. The refined crystal chemical formula is ( Z = 2): Na 2 K 2 Ba 0.7 [(Fe 0.5 Ti 0.1 Mg 0.05 )(H 2 O) 1.3 ]{[Ti 2 (Ti 1.9 Nb 0.1 )(O,OH) 4 ][Si 4 O 12 ] 2 }·4H 2 O. The high‐pressure in situ 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 K = 72 (2) GPa, K ′ 0 = 3.7 (2) and V 0 = 1363 (2) Å 3 . 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: ϵ channel I ≃ 0.85 (4) (cross‐section is rather regular) and ϵ channel 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).