Type-I silicon clathrates containing lithium

The intermetallic phase [LixBa8-x][LiySi46-y] is the first example of a clathrate-I silicide containing lithium with the peculiarity that the Li atoms occupy both cage and framework positions. The phase was obtained by ambient-pressure solid-state reactions at 400 degrees C between Ba4Li2Si6 and the binary clathrate phase Ba8-xSi46 applying different experimental approaches. In this reaction, Li atoms substitute Si atoms of the framework at site 6c (space group Pm (3) over barn) and fill up the Ba-deficient dodecahedral Si-20 cages at site 2a. The presence of Li atoms in the clathrate phase was proven by combined X-ray powder diffraction, Li-7 and Si-29 solid-state NMR analyses. Incorporation of lithium markedly increased the lattice parameter of the clathrate phase, e. g. from a = 10.3200(2)