Influence of p-Type Double-Doping on the Crystals and Electronic Structures of Two Polar Intermetallics: La_(4.57(1))Li_(0.43)Ge_(3.80(3))In_(0.20) and Nd_(4.32(1))Li_(0.68)Ge_(3.87(3))In_(0.13)

摘要

Two quaternary polar intermetallic compounds La_(4.57(1))Li_(0.43)Ge_(3.80(3))In_(0.20) and Nd_(4.32(1))Li_(0.68)Ge_(3.87(3))In_(0.13) were synthesized using a conventional high temperature synthetic method as we attempted to introduce the p-type double-doping of Li and In for RE and Ge in the RE_(5-x)Li_xGe_(4-y) (RE = rare-earth metals) system, and their crystal structures were characterized by single crystal X-ray diffraction experiments. The two title compounds crystallize in the orthorhombic space group Pnma (Pearson code oP16, Z = 4) with six crystallographically independent asymmetric atomic sites and adopt the Gd5Si4-type structure. Overall crystal structures of two isotypic title compounds can be described as a 1:1 assembly of the hypothetical 2-dimensional (2D) RE2(RE/Li)(In/Ge)2 layered structure adopting the Mo2FeB2-type structure and the dumbbell-shaped inter-slab (In/Ge)2 dimers bridging two such neighboring 2D layers along the crystallographic b-axis direction. The observed 'direction selective' structural transformation from the Sm5Ge4-type to the Gd5Si4-type structure can be understood as a result of the simultaneous double-doping by the relatively smaller amount of Li substitution for La at the RE3 site than that in the La4LiGe4 and the partial In substitution for Ge at both of the M1 and M3 sites. The site-preference of In for two particular anionic sites were thoroughly studied using four hypothetical La4LiGe3In models having different atomic arrangements by the tight-binding linear muffin-tin orbital (TB-LMTO) method. The overall electronic structure and individual chemical bonding influenced by the given double-doping were also discussed on the basis of the density of states (DOS) and crystal orbital Hamilton population (COHP) curves analyses.