Ba_4Mo_(12)S_(18):A Superconductor Containing the Dimeric Unit (Mo_6)_2S_(24),the Missing Link between the Mo_6S_(14) and Mo_9S_(17) Units

摘要

The ternary molybdenum chalcogenides M_xMo_6X_8 (M = Na,K,Ca,Sr,Ba,Sn,Pb,lanthanide,3d element;X = S,Se,Te),known as Chevrel phases,have been studied intensively in the last three decades because of their exceptional physical properties.Their crystal structure consists of octahedral Mo_6 clusters surrounded by fourteen chalcogen atoms,eight of which form a distorted cube (i-type ligands),while the remaining six cap the faces of the X_8 cube (alpha-type ligands).In the formalism of Schafer and von Schnering,' such a unit can be written as Mo_6X_8~iX_t~a.