High-Pressure Synthesis and Superconductivity of a New Binary Lanthanum Germanide LaGe3 with Triangular Ge3 Cluster Units

Abstract

We prepared a new binary lanthanum germanide, LaGe(3), under high-pressure and high-temperature conditions (3-12 GPa, 500-1200 °C). It crystallizes in the BaPb(3) structure (the space group R ̅3m) with lattice constants of a = 6.376(1) Å, c = 22.272(3) Å, and V = 784.1(2) Å(3). We refined the structure using Rietveld analysis from X-ray powder data. The structure is composed of two types of close-packed atom layers. In one layer, every La atom is surrounded solely by Ge atoms with the same distance of 3.188 Å. The other layer contains Ge(3) regular, triangular cluster units with a Ge-Ge distance of 2.634 Å. The electron localization function and crystal orbital Hamilton population calculations suggest that the triangular cluster is composed of three Ge-Ge covalent bonds and that each Ge atom has a lone pair. The temperature dependence of the magnetic susceptibility and electrical conductivity measurements revealed that LaGe(3) is metallic and shows superconductivity at 7.4 K. This critical temperature is highest for the La-Ge system.