The dissertation is devoted to an experimental investigation of the chemical interaction of the components in the ternary systems Gd–{Si,Ge}–{Sn,Sb}, establishment of the phase equilibria and construction of the isothermal sections of the phase diagrams at 600°С, synthesis and determination of the crystal structures of the compounds that form in these systems, and derivation of crystal-chemical regularities. The literature available on the phase diagrams of the binary systems Gd–{Si,Ge,Sn,Sb} and {Si,Ge}–{Sn,Sb} and the ternary systems R–Si–Ge and R–{Si,Ge}–{Sn,Sb,Bi}, and on the crystal structures of compounds in these systems was compiled and analyzed. Conclusions were drawn and possible aspects of the interaction of the components in the systems Gd–{Si,Ge}–{Sn,Sb} were predicted. 32 two-component and 167 three-component alloys of the ternary systems Gd–{Si,Ge}–{Sn,Sb}, and three alloys in the related ternary system La–Ge–Bi, were synthesized by arc melting, and annealed at 600°C. Chemical elements in the form of pieces were used as starting materials. The phase composition of the alloys and the crystal structures of the individual phases were determined by X-ray powder diffraction, using patterns obtained on diffractometers STOE Stadi P (radiation Cu Kα1) and DRON-2.0M (radiation Fe Kα). The quantitative elemental composition of individual phases was analyzed by scanning electron microscopy and local energy-dispersive X-ray spectroscopy (scanning electron microscope Tescan Vega 3 LMU with two detectors (secondary electrons and back-scattered electrons), and an energy-dispersive X-ray analyzer Oxford Instruments Aztec ONE with the detector X-MaxN20, and a raster electron microscope REMMA-102-02 with an energy-dispersive X-ray spectrometer EDAR). Based on the experimental results, the phase equilibria at 600°C were determined for the first time and isothermal sections of the phase diagrams of the Gd–{Si,Ge}–{Sn,Sb} systems in the whole concentration region were constructed. The existence of 9 ternary compounds was established. A new ternary compound was synthesized in the related La–Ge–Bi system. The complete crystal structures were determined for all ternary compounds. The main features of the interaction of the components in the systems Gd–{Si,Ge}–{Sn,Sb} were established, the systems were compared with each other and with related ternary systems, and crystal-chemical regularities of the ternary compounds were deduced. The isothermal sections of the phase diagrams of the studied systems are similar in the Gd-rich region but differ from each other in the Gd-poor regions. The solubility of the third component in the binary compounds and the homogeneity ranges of the ternary compounds, are larger in the Gd-rich region of the systems. More ternary compounds are formed in the systems with Ge (6) than in the systems with Si (3), and more ternary compounds are formed in the systems with Sb (5) than in the systems with Sn (4). The compositions of the ternary compounds cover a relatively narrow concentration range, 27-58 at.% Gd, and their crystal structures belong to 7 structure types. The crystal structures of 8 ternary compounds of the Gd–{Si,Ge}–{Sn,Sb} systems have orthorhombic symmetry, and only the structure of the compound Gd5Si0.62Sn3 has hexagonal symmetry. A tendency to ordering of the different chemical elements is observed. In the structures of the ternary compounds of the systems Gd–{Si,Ge}–{Sn,Sb}, the smallest atoms (Si or Ge) are characterized by two types of coordination polyhedron: trigonal prisms and octahedra (trigonal antiprisms). The crystal structures of the ternary compounds Gd2Ge3.84Sn0.92, Gd2Ge2.91Sn0.80, Gd2Ge3.28Sb0.65, and La2Ge3.03Bi0.81 are characterized by partial disorder of Ge and Sn, Sb, or Bi atoms on particular atom sites, as well as by positional disorder of Ge atoms, which was modeled by split positions. The structures of the compounds belong to homologous series of linear intergrowth structures built by the intergrowth of slabs characteristic of simple structure types: (3AlB2|CaF2|Po|CaF2)2 for Gd2Ge3.84Sn0.92, and (3AlB2|2CaF2)2 for Gd2Ge2.91Sn0.80, Gd2Ge3.28Sb0.65, and La2Ge3.03Bi0.81. The crystal structure of the ternary compound GdGe0.85-0.75Sn1.15-1.25 belongs to the homologous series of linear intergrowth structures combining fragments (AlB2|2CaF2)2. Several binary and ternary phases of the general formula Gd5(M1-xM´x)4 (M = Si, Ge; M´ = Sn, Sb) exist along the isoconcentrate of 55.6 at.% Gd in the systems Gd–{Si,Ge}–{Sn,Sb} at 600°С. The structures belong to the related structure types Gd5Si4, Sm5Ge4, and Eu5As4. When the content of Sn or Sb increases, the structure types are adopted in the following order: Gd5Si4 – Sm5Ge4 – Eu5As4. The crystal structure of the ternary compound Gd5Si0.62Sn3 is characterized by an ordered arrangement of the chemical elements and is built by a three-dimensional arrangement of SiGd6 and GdSn6 octahedra.
