TY - JOUR
T1 - Compressibility and crystal structure of sillimanite, Al2SiO5, at high pressure
AU - Yang, H.
AU - Hazen, R. M.
AU - Finger, L. W.
AU - Prewitt, C. T.
AU - Downs, R. T.
PY - 1997/11
Y1 - 1997/11
N2 - The unit-cell dimensions and crystal structure of sillimanite at various pressures up to 5.29 GPa have been refined from single-crystal X-ray diffraction data. As pressure increases, a and b decrease linearly, whereas c decreases nonlinearly with a slightly positive curvature. The axial compression ratios at room pressure are βa:βb:βc=1-22:1.63:1.00. Sillimanite exhibits the least compressibility along c. but the least thermal expansivity along a (Skinner et al. 1961; Winter and Ghose 1979). The bulk modulus of sillimanite is 171(1) GPa with K'-4 (3), larger than that of andalusite (151 GPa), but smaller than that of kyanite (193 GPa). The bulk moduli of the [Al1O6], [Al2O4], and [SiO4] polyhedra are 162(8), 269(33), and 367(89) GPa, respectively. Comparison of high-pressure data for Al2SiO5 polymorphs reveals that the [SiO4] tetrahedra are the most rigid units in all these polymorphic structures, whereas the [AlO6] octahedra are most compressible. Furthermore, [AlO6] octahedral compressibilities decrease from kyanitc to sillimanite, to andalusite, the same order as their bulk moduli, suggesting that [AlO6] octahedra control the compression of the Al2SiO5 polymorphs. The compression of the [Al1O6] octahedron in sillimanite is anisotropic with the longest Al1-OD bond shortening by ∼1.9% between room pressure and 5.29 GPa and the shortest Al1-OB bond by only 0.3%. The compression anisotropy of sillimanite is primarily a consequence of its topological anisotropy, coupled with the compression anisotropy of the Al-O bonds within the [Al1O6] octahedron.
AB - The unit-cell dimensions and crystal structure of sillimanite at various pressures up to 5.29 GPa have been refined from single-crystal X-ray diffraction data. As pressure increases, a and b decrease linearly, whereas c decreases nonlinearly with a slightly positive curvature. The axial compression ratios at room pressure are βa:βb:βc=1-22:1.63:1.00. Sillimanite exhibits the least compressibility along c. but the least thermal expansivity along a (Skinner et al. 1961; Winter and Ghose 1979). The bulk modulus of sillimanite is 171(1) GPa with K'-4 (3), larger than that of andalusite (151 GPa), but smaller than that of kyanite (193 GPa). The bulk moduli of the [Al1O6], [Al2O4], and [SiO4] polyhedra are 162(8), 269(33), and 367(89) GPa, respectively. Comparison of high-pressure data for Al2SiO5 polymorphs reveals that the [SiO4] tetrahedra are the most rigid units in all these polymorphic structures, whereas the [AlO6] octahedra are most compressible. Furthermore, [AlO6] octahedral compressibilities decrease from kyanitc to sillimanite, to andalusite, the same order as their bulk moduli, suggesting that [AlO6] octahedra control the compression of the Al2SiO5 polymorphs. The compression of the [Al1O6] octahedron in sillimanite is anisotropic with the longest Al1-OD bond shortening by ∼1.9% between room pressure and 5.29 GPa and the shortest Al1-OB bond by only 0.3%. The compression anisotropy of sillimanite is primarily a consequence of its topological anisotropy, coupled with the compression anisotropy of the Al-O bonds within the [Al1O6] octahedron.
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U2 - 10.1007/s002690050084
DO - 10.1007/s002690050084
M3 - Article
AN - SCOPUS:0031425971
SN - 0342-1791
VL - 25
SP - 39
EP - 47
JO - Physics and Chemistry of Minerals
JF - Physics and Chemistry of Minerals
IS - 1
ER -