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

• Site-preference between anions was elucidated by the QVAL value of each site.
• Ten models with different atomic orderings were examined by coloring problems.
• COHP curves explained the anisotropic size-change of La11Ge4In5.00(1)Li1.00.

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.

Reported is experimental and theoretical studies to understand the site-preference between anionic elements and the anisotropic size-change of the 3-D anionic frameworks of two polar intermetallic compounds in the RE11Ge4In6−xMx (RE = La, Ce; M = Li, Ge; x = 1, 1.96) phase. Indium atoms with a smaller electronegativity prefer to occupy the “dumbbell-site” having the smaller QVAL value, and the anisotropic size-change of the anionic framework in La11Ge4In5.00(1)Li1.00 is rationalized by using various COHP curves analyses.Figure optionsDownload as PowerPoint slide