TY - JOUR

T1 - Raman spectroscopy of chibaite, natural MTN silica clathrate, at high pressure up to 8 GPa

AU - Likhacheva, Anna Yu

AU - Goryainov, Sergey V.

AU - Seryotkin, Yuriy V.

AU - Litasov, Konstantin D.

AU - Momma, Koichi

PY - 2016/4/1

Y1 - 2016/4/1

N2 - The high-pressure behavior of chibaite, newly discovered natural clathrasil isotypical to gas hydrate sII, with ideal formula 136SiO2·24X (X = CH4, C2H6, C3H8, C4H10), was studied by Raman spectroscopy up to 7.7 GPa with a diamond anvil cell, using KBr as a pressure transmitting medium. The chibaite structure is preserved throughout the whole pressure range. The deviation from regular shift and appearance of new bands in the lattice spectrum is observed at about 1.2 and 3.5 GPa. As concerns the guest hydrocarbon molecules, the high-frequency shifts of their C-C and C-H bands are almost monotonic within the whole pressure range, showing only slight bends at 1.2 and 3.5 GPa. The FWHMs of stretching C-C and C-H bands demonstrate a high sensitivity to pressure, more pronounced at 1.2 GPa. The obtained data allow to suggest two reversible structural transformations in chibaite at about 1.2 and 3.5 GPa, associated with the distortion of framework cages and corresponding ordering of the guest hydrocarbon molecules. The role of 'guest molecule/host cage' dimensional ratio determining the HP behavior of MEP and MTN clathrasils is discussed.

AB - The high-pressure behavior of chibaite, newly discovered natural clathrasil isotypical to gas hydrate sII, with ideal formula 136SiO2·24X (X = CH4, C2H6, C3H8, C4H10), was studied by Raman spectroscopy up to 7.7 GPa with a diamond anvil cell, using KBr as a pressure transmitting medium. The chibaite structure is preserved throughout the whole pressure range. The deviation from regular shift and appearance of new bands in the lattice spectrum is observed at about 1.2 and 3.5 GPa. As concerns the guest hydrocarbon molecules, the high-frequency shifts of their C-C and C-H bands are almost monotonic within the whole pressure range, showing only slight bends at 1.2 and 3.5 GPa. The FWHMs of stretching C-C and C-H bands demonstrate a high sensitivity to pressure, more pronounced at 1.2 GPa. The obtained data allow to suggest two reversible structural transformations in chibaite at about 1.2 and 3.5 GPa, associated with the distortion of framework cages and corresponding ordering of the guest hydrocarbon molecules. The role of 'guest molecule/host cage' dimensional ratio determining the HP behavior of MEP and MTN clathrasils is discussed.

KW - Guest hydrocarbons

KW - High pressure

KW - Natural clathrasil

KW - Raman spectroscopy

UR - http://www.scopus.com/inward/record.url?scp=84950270230&partnerID=8YFLogxK

U2 - 10.1016/j.micromeso.2015.11.033

DO - 10.1016/j.micromeso.2015.11.033

M3 - Article

AN - SCOPUS:84950270230

VL - 224

SP - 100

EP - 106

JO - Microporous and Mesoporous Materials

JF - Microporous and Mesoporous Materials

SN - 1387-1811

ER -