Filled platinum germanium skutterudites MPt4Ge12 (M = Sr, Ba, La—Nd, Sm, Eu): crystal structure and chemical bonding

Abstract

The crystal structures of filled skutterudite compounds MPt 4 Ge 12 (M = Sr, Ba, La—Nd, Sm, Eu) with LaFe 4 P 12 type structure were refined from single crystal data. Depending on the size of the M species, displacement parameters of filler atoms M can be similar or much larger than those of Pt and Ge. We discuss the MPt 4 Ge 12 skutterudites in a crystal chemical framework of related structure types. Electronic structure calculations and chemical bonding analysis by the electron localizability indicator describe the MPt 4 Ge l2 compounds as covalently bonded polyanionic [Pt 4 Ge 12 ] framework structures which are stabilized by electron transfer from the filler metal-ions M. In case of 3d metal containing filled skutterudite compounds the DOS at the Fermi level is dominated by contributions of 3d metal states. In contrast, for the MPt 4 Ge 12 compounds, it is essentially composed of Ge p states with Pt 5d contributions at significantly lower energies.