High-pressure synthesis and superconductivity of LaGe5 containing a tunnel germanium network

Superconducting LaGe5 was synthesized by the reaction of La and Ge mixtures under a pressure of 5 GPa at 1200°C. It crystallized in the orthorhombic space group Immm (No. 71) with a=4.0290(6), b =6.307(1), and c=9.978(2) Å, V=253.54(6) Å3, and Z=2. Single-crystal studies revealed that LaGe5 had a germanium network with tunnels running along the a axis, where La atoms are located. There are two crystallographically different Ge sites in the structure La[(Gel)4(Ge2)1]. The tunnel network is composed of folded sp3-Gel layers coupled by eight coordinated Ge2 atoms. Electrical resistivity and magnetic-susceptibility measurements showed that the compound was a type-II superconductor with a transition temperature of 7.0 K