Eu4Ga8Ge16:: A new four-coordinate clathrate network

We report a new clathrate phase composed of europium atoms occupying cage voids in a gallium/germanium tetrahedral cage network. Eu4Ga8Ge16 crystallizes in orthorhombic space group Cmcm with a = 4.1349(6), b = 11.2842(15), and c = 13.2408(18). The compound is believed to satisfy the Zintl-Klemm concept of bonding to form a network solid with a unique one-dimensional line of Eu atoms aligned along the crystallographic a-axis, charge balancing an electron-deficient Ga/Ge framework. The compound was observed to melt incongruently at 684(1) degreesC by differential thermal analysis (DTA). Single-crystal electrical conductivity measurements gave 130 S/cm at room temperature with a metallic temperature dependence. The room-temperature thermopower (Seebeck coefficient) was measured to be 40 muV/K.