Delenko T. Isothermal sections (600°С) of the phase diagrams and crystal structures of compounds of the systems {Dy,Yb}–Ga–{Si,Ge}

By means of X-ray phase and structure analyzes, scanning electron microscopy and local energy-dispersive X-ray spectroscopy, the phase equilibria and crystal structure of compounds in the ternary systems {Dy,Yb}–Ga–{Si,Ge} at 600°С were determined. Isothermal sections of the phase diagrams of these systems at 600°С were constructed in the whole concentration range for the first time. The formation of 22 ternary compounds, 11 of which are new, was established in these systems. In the related systems {Tb,Ho}–Ga–Ge and Ho–Ga–Si, four new ternary compounds were synthesized. The crystal structures of 15 new compounds were determined and the homogeneity ranges of three other ternary compounds were established. The temperature dependencies of the electrical resistivity were measured for three compounds, DyGa2.68Ge0.32, DyGa2.32Ge0.68, and YbGa1.13Si0.87, and differential thermoelectric power was measured for DyGa2.68Ge0.32 and DyGa2.32Ge0.68. The structure types that exist in the systems Dy–Ga–{Si,Ge} at 25 at.% Dy belong to the family of close-packed structures: structure types Ta(Rh0.33Pd0.67)3 (hP40, P63/mmc, (hhchc)2), Mg3In (hR48, R-3m, (hhcc)2), PuAl3 (hP24, P63/mmc, (hcc)2), and Cu3Au (cP4, Pm-3m, (c)3). Substitution of p-element atoms of group ІV (Si, Ge) for Ga leads to the formation of structures with lower hexagonality (60-0 % within the composition range 0-35 at.% Ge). The structures of the compounds Dy2Ga2.23-1.24Ge4.77-5.76 and DyGa0.12Ge1.80 belong to homologous seria of structures formed by linear intergrowth of slabs characteristic of simple structure types: BaAl4 (tI10, I4/mmm), AlB2, and α-Po (cP1, Pm-3m) for Dy2Ga2.23-1.24Ge4.77-5.76, and AlB2 and CaF2 (cF12, Fm-3m) for DyGa0.12Ge1.80. The structures of the ternary compounds with 33.3-40.0 at.% rare-earth element are characterized by trigonal-prismatic coordination of the р-element atoms. The compositions of the compounds are determined by the valence electron concentration (2-4 bonds for VECM = 6-4 per p-element atom). At the transition from close-packed structures to structures with trigonal-prismatic coordination of the р-element atoms, a tendency toward contraction of the interatomic distances (increase of the interaction between the p-element atoms) is observed.