TY - JOUR

T1 - Evolution of the bikitaite structure at high pressure

T2 - A single-crystal X-ray diffraction study

AU - Seryotkin, Yurii V.

PY - 2016/5/15

Y1 - 2016/5/15

N2 - The structural evolution of natural bikitaite Li2(H2O)2[Al2Si4O12], compressed in penetrating (water-containing) medium up to 4 GPa, was studied using single-crystal X-ray diffraction data from a diamond-anvil cell. A nearly isotropic compression of bikitaite up to 1.2 GPa proceeds through a slight decrease of the framework T-O-T angles. Further pressurizing leads to anisotropic compression: The compressibility of b-axis is half as smaller compared to c-axis, and the a-axis is the least compressible. The structure can be described as hexagonal sheets of six-membered rings parallel to (001), connected by pyroxene-like chains. Upon the compression, the hexagonal sheets approach each other, leading to the shortening of the c-parameter. The deformation of hexagonal sheets, reinforced by O-Li bonds, is defined by the corrugation of 6-membered rings. The deformation of more flexible pyroxene chains, responding to the deformation of hexagonal sheets, consists of axial rotation of tetrahedra with only minor change in T-O-T angles. The arrangement of extraframework species changed slightly. The system of H-bonds between water molecules remains intact upon pressurizing. At the same time, the formation of new H-bonds with framework O-atoms becomes possible above 2 GPa due to the shortening of the distances between Ow positions and framework O-atoms. All pressure-induced structural changes are completely reversible and the recovered crystal structure returns to its ambient structure. The results clearly demonstrate the absence of pressure-induced hydration in the bikitaite structure. The pressure-induced changes in the unit cell metrics are similar for bikitaite compressed in water-containing medium, silicon oil, and glycerol.

AB - The structural evolution of natural bikitaite Li2(H2O)2[Al2Si4O12], compressed in penetrating (water-containing) medium up to 4 GPa, was studied using single-crystal X-ray diffraction data from a diamond-anvil cell. A nearly isotropic compression of bikitaite up to 1.2 GPa proceeds through a slight decrease of the framework T-O-T angles. Further pressurizing leads to anisotropic compression: The compressibility of b-axis is half as smaller compared to c-axis, and the a-axis is the least compressible. The structure can be described as hexagonal sheets of six-membered rings parallel to (001), connected by pyroxene-like chains. Upon the compression, the hexagonal sheets approach each other, leading to the shortening of the c-parameter. The deformation of hexagonal sheets, reinforced by O-Li bonds, is defined by the corrugation of 6-membered rings. The deformation of more flexible pyroxene chains, responding to the deformation of hexagonal sheets, consists of axial rotation of tetrahedra with only minor change in T-O-T angles. The arrangement of extraframework species changed slightly. The system of H-bonds between water molecules remains intact upon pressurizing. At the same time, the formation of new H-bonds with framework O-atoms becomes possible above 2 GPa due to the shortening of the distances between Ow positions and framework O-atoms. All pressure-induced structural changes are completely reversible and the recovered crystal structure returns to its ambient structure. The results clearly demonstrate the absence of pressure-induced hydration in the bikitaite structure. The pressure-induced changes in the unit cell metrics are similar for bikitaite compressed in water-containing medium, silicon oil, and glycerol.

KW - Bikitaite

KW - Compressibility

KW - Crystal structure

KW - High pressure

KW - Single-crystal X-ray diffraction

KW - Zeolite

UR - http://www.scopus.com/inward/record.url?scp=84959421851&partnerID=8YFLogxK

U2 - 10.1016/j.micromeso.2016.02.021

DO - 10.1016/j.micromeso.2016.02.021

M3 - Article

AN - SCOPUS:84959421851

VL - 226

SP - 415

EP - 423

JO - Microporous and Mesoporous Materials

JF - Microporous and Mesoporous Materials

SN - 1387-1811

ER -