Combined effect of chemical pressure and valence electron concentration through the electron-deficient Li substitution on the RE4LiGe4 (RE=La, Ce, Pr, and Sm) system

Abstract

Four members of the RE 4 LiGe 4 ( RE =La, Ce, Pr, and Sm) system have been prepared by high-temperature reaction method and characterized by X-ray diffractions. All compounds crystallize in the orthorhombic Gd 5 Si 4 -type structure (space group Pnma , Pearson code oP 16) with bonding interactions for interslab Ge 2 dimers. The Li substitution for rare-earth elements in the RE 4 LiGe 4 system leads to a combined effect of the increased chemical pressure and the decreased valance electron concentration (VEC), which eventually results in the structure transformation from the Sm 5 Ge 4 -type with all broken interslab Ge–Ge bond for the parental RE 5 Ge 4 to the Gd 5 Si 4 -type structure for the ternary RE 4 LiGe 4 ( RE =La, Ce, Pr, and Sm) system. Site-preference between rare-earth metals and Li is proven to generate energetically the most favorable atomic arrangements according to coloring-problem, and the rationale is provided using both the size-factor and the electronic-factor related, respectively, to site-volume and electronegativity as well as QVAL values. Tight-binding, linear-muffin-tin-orbital (TB-LMTO) calculations are performed to investigate electronic densities of states (DOS) and crystal orbital Hamilton population (COHP) curves. The influence of reduced VEC for chemical bonding including the formation of interslab Ge 2 dimers is also discussed. The magnetic property measurements prove that the non-magnetic Li substitution leads to the ferromagnetic (FM)-like ground state for Ce 4 LiGe 4 and the co-existence of antiferromagntic (AFM) and FM ground states for Sm 4 LiGe 4 . Reported is a combined effect of the chemical pressure and the reduced VEC caused by the smaller monovalent non-magnetic Li substitution for the larger trivalent magnetic rare-earth metals in the RE 4 LiGe 4 ( RE =La, Ce, Pr, and Sm) system. This results in the structure transformation from the Sm 5 Ge 4 -type to the Gd 5 Si 4 -type structure and the changes in magnetic properties. • Four Li-containing intermetallic compounds RE 4 LiGe 4 ( RE =La, Ce, Pr and Sm) were synthesized. • The combined effect of the chemical pressure and the reduced VEC caused by Li substitution for a rare-earth metal results in the structure transformation. • Electronic structures and magnetic properties of title compounds were thoroughly investigated.