Experimental and theoretical investigations for site preference and anisotropic size change of RE11Ge4In6−xMx (RE = La, Ce; M = Li, Ge; x = 1, 1.96)

Abstract

Two polar intermetallic compounds in the RE11Ge4In6−xMx (RE=La, Ce; M=Li, Ge; x=1, 1.96) series have been synthesized by conventional high-temperature reactions and characterized by both single-crystal and powder X-ray diffractions. Both compounds crystallized in the tetragonal crystal system (space group I4/mmm, Z=4, Pearson symbol tI84) with nine crystallographically independent atomic positions in the asymmetric unit and adopted the Sm11Ge4In6-type structure, which can be considered as an ordered version of the Ho11Ge10-type. The lattice parameters are a=11.8370(4)Å and c=17.2308(7)Å for La11Ge4In5.00(1)Li1.00; a=11.8892(4)Å, c=16.5736(7)Å for Ce11Ge5.96(3)In4.04. The overall crystal structures of two isotypic compounds can be described as a combination of the cage-shaped 3-dimensional (3-D) anionic framework and three different types of cationic polyhedra filling the inside of the 3-D frameworks. Anionic elements consisting of the frameworks indicate the particular site preference, which can be understood by QVAL values. Theoretical investigations using tight-binding linear muffin-tin orbital (LMTO) method provide rationales for the anisotropic size change of the unit cell of La11Ge4In5.00(1)Li1.00 using the various crystal orbital Hamilton population (COHP) curves and the possible short-range anionic ordering based on total electronic energy comparisons. Density of states (DOS) curves are also analyzed to explain the orbital interactions among components in the given crystal structure.