ABSTRACT
Clathrates are periodic solids in which tetrahedrally bonded atoms form a three-dimensional framework of cages that enclose guest atoms, which do not engage in covalent bonds with the host lattice. še clathrate type-I structure consists of a host lattice of 24-vertex tetrakaidecahedra [51262] (12 pentagonal and 2 hexagonal faces), which share hexagonal faces and form nonintersecting channels enclosing isolated 20-vertex pentagon dodecahedra [512]. Structures of type-I crystallize in the centrosymmetric space group Pm 3 n (No. 223; Pearson symbol cP54). šis clathrate type-I framework contains 46 atoms E distributed over three sites*: 6d, 16i, and 24k. Filler (guest) atoms G are incorporated (clathrated) in two small cavities (site 2a) at the centers of pentagon dodecahedra and in six larger cavities (site 6c) at the centers of tetrakaidecahedra, resulting in a general formula G2+6[E46] (for details see Ref. [1]).
