Thermal, Magnetic, Electronic, and Superconducting Properties of Rare‐Earth Metal Pentagermanides REGe5 (RE = La, Nd, Sm, Gd) and Synthesis of TbGe5

Abstract

AbstractA series of isotypic rare‐earth metal pentagermanides including the new compound TbGe5 were prepared by high‐pressure synthesis. They crystallize in the orthorhombic space group Immm [No. 71; a = 395.70(9) pm; b = 611.1(2) pm, and c = 983.6(3) pm for TbGe5]. The crystal structure is isotypic to LaGe5 and consists of puckered germanium slabs, which sandwich a second germanium species and the rare‐earth metal atoms. At ambient pressure, the thermal decomposition of the phases REGe5 (RE = La, Nd, Sm, Gd, and Tb) proceeds via discrete intermediate steps into Ge(cF8) and thermodynamically stable germanium‐poorer phases. The investigated compounds REGe5 are paramagnetic metallic conductors, which order antiferromagnetically at low temperatures. Specific heat measurements reveal that the superconducting state of LaGe5 below Tc = 7.1(1) K is characterized by a critical field of μ0Hc2 = 0.2 T and weak electron‐phonon coupling. Density‐functional based band‐structure calculations yield a very similar electronic structure for all the isotypic REGe5 compounds. Besides a slight increase in the width of the valence band for smaller RE atoms, only minor differences are found for the two different germanium environments.