Pukas S. Crystal structure of metallides based on the Gd and Er disilicides and digermanides and p-elements of the group III

The interaction of the components in the systems {Gd,Er}-{Al,Ga}-{Si,Ge} was investigated and isothermal sections (873 or 1073 K) of the phase diagrams of these systems were constructed in the region of disilicides and digermanides of rare-earth metals. The crystal structures of 22 new and 9 previously known compounds were determined by X-ray, powder and single-crystal methods, and electron diffraction. The existence of three new structure types, Er3Si5-x, ErGe0.77Si0.83, and Er4Ga2.72Si3.28, was established. The modulated structure of the silicide Er3Si5-x was determined for the first time. The origin of the structural deformations taking place in the ternary compounds during the transformation from the tetragonal a-ThSi2-type structure (ErGe0.82Si0.70) to the orthorhombic a-GdSi2-type structure (ErGe0.77Si0.83) was examined. The number of valence electrons is the main criteria for the formation of silicides (germanides) of rare-earth metals with the structure types AlB2, a-ThSi2, their vacancy derivatives, and representatives of the homologous series based on AlB2- and CaF2- or W-type slabs. A row of isostructural compounds of rare-earth germanides with the ZrSi2 (or ErGe2.16) structure type was found.