[en] Vibration spectra of double oxides with the structure of rhombic perovskite LnRhO₃ (Ln=Pr, Gd, Lu) are investigated. Infrared spectra character is found to change depending on the degree of rhombic distortion of perovskite crystalline lattice. Theoretical calculation of spectra obtained is carried out according to the method of polymer chains in a valency-force approximation. A reference of frequencies is suggested. Nontypicalness of the most part of vibrations and a great influence of rare earth elements nature on the formation character of cation-anion bond are noted

[en] In this paper, the present state of knowledge of crystalline electric field (CEF) in two important classes of ternary superconductors has been described. It is clear that in understanding the superconducting and magnetic behavior of RERh₄B₄, the CEF plays a very important role. Considerable importance has been given to the specific heat Schottky anomalies in deducing the position and degeneracy of various CEF levels. Interpretation of these data is made difficult because of complicated subtraction of lattice, electronic and superconducting specific heats. Furthermore, the purity of the sample is important in such studies. It is known that a few percent of Rh-B/sub x/, RERh₃B₂ and RERh₆B₄ are commonly present in RERh₄B₄, while Mo-Ch/sub x/, RE-Ch/sub x/ and RE₂O₂Ch phases occur in Chevrel phase compounds. Only single-crystal samples will lead to dependable specific heat data

[en] Using the Mori formalism, a general theory is developed for the calculation of paramagnetic relaxation effects in a general crystal field doublet. For systems with extreme magnetic anisotropy, the relaxation rates show a strong angular dependence, being severely peaked in a direction perpendicular to the magnetic easy axis. Application to the RRh₄B₄ (R = rare-earth) compounds is discussed. 5 refs

[en] New binary oxides CeRhO₃ and YRhO₃ have been obtained by the reactions of Rh₂O₃ with Y₂O₃ at 1000 deg C in air and with Ce₂(CO₃)₃ at 500-850 deg C in a nitrogen atmosphere. Both compounds have a structure of rhombically distorted perovskite, are isostructural with other similar oxides LnRhO₃, and possess semiconducting properties. Thermal stability of new compounds in a nitrogen and air atmosphere has been studied and infrared spectroscopical investigation of CeRhO₃ and YRhO₃ has been conducted. The relationship between the cell volume of the compounds LnRhO₃ and Ln³⁺ ionic radius has been plotted. Crystallochemical aspects of the formation of M³⁺RhO₃ and the existence regions of possible structural types of these compounds depending on the ionic radius of M³⁺ are discussed

No abstract available

[en] Using the methods of monocrystal and powder it is established that RRhC₂(R=La, Ce) structures belong to a new type, and RRhC₂ (R=Pr, Nd, Sm) - to the CeNiC₂ structural type. The LaRhC₂ crystal structure (sp.gr. P4₁, a=0.3981(1), c=1.5351(5) nm, Z=4) is determined. The coordinates of atoms are refined by the least-squares method (LSM) in anisotropic (La, Rh) and isotropic (C) approximation up to R=0.030. The lattice periods of RRhC₂ compounds (R=Ce, Pr, Nd, Sm) are LSM refined

[en] The magnetic ordering temperatures of the primitive tetragonal rare earth (RE) rhodium boride compounds exhibit a peak at DyRh₄B₄ rather than GdRh₄B₄ as predicted from ordering via the indirect RKKY exchange interaction. This deviation is analyzed in terms of the depression of the superconducting transition temperature of LuRh₄B₄ by dilute amounts of RE impurity ions and the magnetic heat capacities of the RERh₄B₄ compounds for RE = Gd, Tb, Dy, and Ho. The strength of anisotropic crystalline electric field forces, as inferred from magnetic entropy considerations, may be the origin of the anomalous magnetic ordering temperatures. In addition, the depression of the superconducting transition temperatures of ErRh₄B₄ and TmRh₄B₄ from that of LuRh₄B₄ is shown to arise primarily from elastic exchange scattering of the conduction electrons by the magnetic RE ions

[en] Crystallochemical analysis of all known compounds containing rhodium atoms in chalcogen atoms surrounding in their structure was carried out using the Voronoi-Dirichlet polyhedra and method of intersecting spheres. It was ascertained that Rh atoms manifest coordination number 6, 5 or 4 towards S, Se or Te atoms, moreover, besides the bonds with chalcogens, rhodium atoms can form additionally from 1 to 4 bonds with metal atoms. It was determined that for Rh(III), Rh(2.67) and Rh(II) atoms in selenides and tellurides the volume of the Voronoi-Dirichlet polyhedra actually does not depend on valency state, whereas in sulfides it increases regularly with decrease in metal oxidation state from Rh(III) to Rh(I)

[en] The interaction of superconductivity and long-range magnetic order was examined in various ternary and pseudoternary rare earth rhodium boride compounds. Upper critical magnetic field H_c2 measurements obtained from resistance data demonstrate that LuRh₄B₄ is a type II superconductor with H_c2(0) = 60 kOe and a Ginzburg-Landau parameter k approx. = 23. These upper critical field results are compared with those which were obtained using ac magnetic susceptibility data

[en] The magnetic properties of the RRh₄B₄ (R represents rare-earth metal) compounds are discussed in terms of a combined crystalline-electric-field and molecular-field approach. Magnetization data taken on single-crystal ErRh₄B₄ in five orientations are used to obtain the crystal-field and molecular-field coefficients, resulting in a complete analysis for the paramagnetic properties of this compound. The crystal-field parameters are additionally used to discuss all previously published magnetic data for polycrystalline RRh₄B₄ compounds. For these highly anisotropic materials, the effect of preferential crystallite orientation on the observed data is pointed out. Consideration of the variation of the magnetic transition temperature T/sub m/ between different constituent rare earths has verified a previous conclusion that the crystal field has a pronounced effect on T/sub m/, but this alone does not fully explain the observations