TY - JOUR
T1 - Neutron diffraction study of the type i clathrate Ba 8Al xSi 46-x
T2 - Site occupancies, cage volumes, and the interaction between the guest and the host framework
AU - Roudebush, John H.
AU - De La Cruz, Clarina
AU - Chakoumakos, Bryan C.
AU - Kauzlarich, Susan M.
PY - 2012/2/6
Y1 - 2012/2/6
N2 - Samples with the type I clathrate structure and composition Ba 8Al xSi 46-x, where x = 8, 10, 12, 14, and 15, were examined by neutron powder diffraction at 35 K. The clathrate type I structure contains Ba cations as guests in a framework derived from tetrahedrally coordinated Al/Si atoms. The framework is made up of five- and six-membered rings that form dodecahedral and tetrakaidecahedral cages. The change in distances between tetrahedral sites across the series is used to develop a model for the mixed Al/Si occupancy observed in the framework. The calculated volumes of the cages that contain the Ba atoms display a linear increase with increasing Al composition. In the smaller dodecahedral cages, the Ba atomic displacement parameter is symmetry constrained to be isotropic for all compositions. In the larger tetrakaidecahedral cages, the anisotropic atomic displacement of the Ba atom depends upon the composition: the displacement is perpendicular (x = 8) and parallel (x = 15) to the six-membered ring. This difference in direction of the displacement parameter is attributed to interaction with the Al in the framework and not to the size of the cage volume as x increases from 8 to 15. The influence of the site occupation of Al in the framework on displacement of the cation at the 6d site is demonstrated.
AB - Samples with the type I clathrate structure and composition Ba 8Al xSi 46-x, where x = 8, 10, 12, 14, and 15, were examined by neutron powder diffraction at 35 K. The clathrate type I structure contains Ba cations as guests in a framework derived from tetrahedrally coordinated Al/Si atoms. The framework is made up of five- and six-membered rings that form dodecahedral and tetrakaidecahedral cages. The change in distances between tetrahedral sites across the series is used to develop a model for the mixed Al/Si occupancy observed in the framework. The calculated volumes of the cages that contain the Ba atoms display a linear increase with increasing Al composition. In the smaller dodecahedral cages, the Ba atomic displacement parameter is symmetry constrained to be isotropic for all compositions. In the larger tetrakaidecahedral cages, the anisotropic atomic displacement of the Ba atom depends upon the composition: the displacement is perpendicular (x = 8) and parallel (x = 15) to the six-membered ring. This difference in direction of the displacement parameter is attributed to interaction with the Al in the framework and not to the size of the cage volume as x increases from 8 to 15. The influence of the site occupation of Al in the framework on displacement of the cation at the 6d site is demonstrated.
UR - http://www.scopus.com/inward/record.url?scp=84856714165&partnerID=8YFLogxK
U2 - 10.1021/ic202095e
DO - 10.1021/ic202095e
M3 - Article
AN - SCOPUS:84856714165
SN - 0020-1669
VL - 51
SP - 1805
EP - 1812
JO - Inorganic Chemistry
JF - Inorganic Chemistry
IS - 3
ER -