Ternary lithium stannides Li xT 3Sn 7−x ( T=Rh, Ir)

Abstract

The ternary stannides Li x Rh 3Sn 7− x ( x = 0.45 , 0.64, 0.80) and Li x Ir 3Sn 7− x ( x = 0.62 and 0.66) were synthesized from the elements in sealed tantalum tubes in a water-cooled sample chamber of an induction furnace. The samples were characterized by X-ray diffraction on powders and single crystals. The stannides adopt the cubic Ir 3Ge 7-type structure (space group Im 3 ¯ m , Z=4). In this structure type the tin atoms occupy the Wyckoff positions 12 d and 16 f and form two interpenetrating frameworks consisting of cubes and square antiprisms. The rhodium and iridium atoms center the square antiprisms and are arranged in pairs. With increasing lithium substitution the lattice parameter of Ir 3Sn 7 (936.7) decreases via 932.2 pm ( x = 0.62 ) to 931.2 pm ( x = 0.66 ), while the Ir–Ir distance remains almost the same (290 pm). A similar trend is observed for the rhodium compounds. The lithium atoms substitute Sn on both framework sites. However, the 16 f site shows a substantially larger preference for Li occupation. This is in contrast to the isotypic magnesium based compounds.