Study of New Ternary Rare-Earth Intermetallic Germanides with Polar Covalent Bonding : Beyond the Zintl Picture

The thesis focuses on the syntheses, structural characterizations and chemical bonding analyses for several ternary R-M-Ge (R = rare earth metal; M = another metal) intermetallics. The challenges in understanding the main interactions governing the chemistry of these compounds, which lead to our inability to predict their formation, structure and properties, are what provided the motivation for this study. In particular, the R₂MGe₆ (M = Li, Mg, Al, Cu, Zn, Pd, Ag), R₄MGe_10-x (M = Li, Mg), R2Pd₃Ge₅, Lu₅Pd₄Ge₈, Lu₃Pd₄Ge₄ and Yb₂PdGe₃ phases were synthesized and structurally characterized. Much effort was put into the stabilization of metastable phases, employing the innovative metal flux method, and into the accurate structure solution of twinned crystals. Cutting-edge position-space chemical bonding techniques were combined with new methodologies conceived to correctly describe the Ge-M, Ge-La and also La-M polar-covalent interactions for the La₂MGe₆ (M = Li, Mg, Al, Cu, Zn, Pd, Ag) series. The present results constitute a step forward in our comprehension of ternary germanide chemistry as well as providing a good playground for further investigations.