Solid State Phenomena Vol. 289

Abstract: The phase equilibria in the ternary systems {Ce, Gd}–{Ti, Zr}–Sb were investigated by means of X-ray powder diffraction and energy-dispersive X-ray spectroscopy. The isothermal sections of the phase diagrams at 600°C were constructed. The formation of three ternary compounds (Ce₂Ti₇Sb₁₂, Ce₃TiSb₅, and Gd₂Ti₁₁Sb₁₄) was confirmed in the {Ce, Gd}–Ti–Sb systems and no more ternaries were found. The investigation of the {Ce, Gd}–Zr–Sb systems revealed several new ternary compounds and confirmed the known ones. The crystal structure of the new compound Ce_0.08(3)Zr_1.92(3)Sb was determined from X-ray powder diffraction data. The other new compounds in the Ce–Zr–Sb system were found to have compositions close to ~CeZrSb₄ and ~Ce₂Zr₃Sb₅. In the Gd–Zr–Sb system the existence of a large homogeneity range was established for the GdZrSb compound along the isoconcentrate 33.3 at.% Sb: Gd_1-xZr_1+xSb (x = 00.905(18) at 600°C), and a new compound, ~Gd₃Zr₃Sb₁₄, was discovered. The crystal structures at the boundary compositions of the Gd_1-xZr_1+xSb phase were refined from X-ray powder diffraction data.

Abstract: The isothermal section of the phase diagram of Tb–Fe–C system at 800 °C was studied in the full concentration range using powder X-ray phase and structure analyses, and energy-dispersive X-ray spectroscopy. Six ternary compounds Tb_1.88Fe₁₄C, Tb₁₃Fe₁₀C₁₃, TbFeC₂, Tb₁₅Fe₈C₂₅, Tb_5.64Fe₂C₉, Tb₂FeC₄ and a limited solid solubility of carbon in the crystal structure of the binary parent compound Tb₂Fe₁₇C_х (0≤ х ≤0.8) have been found to exist at 800 °C. The crystal structures of two new ternary carbides have been determined by means of powder X-ray diffraction: Tb₁₅Fe₈C₂₅ with structure type Er₁₅Fe₈C₂₅, space group P321, a = 11.9706(3) Å, c = 5.1733(2) Å, R_B(I) = 0.07, R_P = 0.06, R_Pw = 0.08, and Tb₁₃Fe₁₀C₁₃ with structure type Gd₁₃Fe₁₀C₁₃, space group P3₁21, a = 9.1800(9) Å, c = 23.703(5) Å, R_B(I) = 0.04, R_P = 0.16. Both compounds are representatives of the carbometalate class of complex carbides. Tb₁₅Fe₈C₂₅ displays an itinerant ferro-or ferrimagnetic ordering of the Fe 3d-moments below T_M ≈ 50 K while Tb 4f-moments remain essentially paramagnetic at least down to about 10 K.

Abstract: Nine new quaternary R₃MnAl₃Ge₂ alumogermanides (R = Sm, Gd-Lu) were synthesized by arc melting and their crystal structures were studied by X-ray powder diffraction. All of the compounds crystallize in hexagonal Y₃NiAl₃Ge₂-type structures: Pearson symbol hP9, space group P-62m. The unit-cell parameters of the isotypic compounds decrease with decreasing radius of the rare-earth metal. The hexagonal structure type Y₃NiAl₃Ge₂ (Z = 1) is a quaternary ordering variant of the binary type Fe₂P (Z = 3) and the ternary types β₁-K₂UF₆, Lu₃CoGa₅, Zr₃Cu₄Si₂ (Z = 1), ZrNiAl (Z = 3). It belongs to the family of structures with trigonal prismatic coordination of the small atoms.

Abstract: The isothermal section at 800°C of the phase diagram of the ternary system Sc–Cu–Al was constructed in the whole concentration range using X-ray powder diffraction data. The existence of eight ternary compounds was confirmed: ScCu_4.9‑6.0Al_7.1‑6.0 (structure type ThMn₁₂, Pearson symbol tI26, space group I4/mmm), Sc₆Cu_24.1Al_11.9 (own structure type, cI176, Im-3), Sc₂Cu_6.25Al_4.75 (own structure type, oS108, Cmmm), Sc₃Cu_7.5Al_7.5 (Sc₃Ni₁₁Ge₄, hP38, P6₃/mmc), ScCu₂Al (MnCu₂Al, cF16, Fm-3m), ScCu_0.8Al_0.2 (CsCl, cP2, Pm-3m), ScCu_0.6Al_1.4 (MgNi₂, hP24, P6₃/mmc), and ScCuAl (MgZn₂, hP12, P6₃/mmc), and the existence of a continuous solid solution ScCu_1-xAl_x (x = 0-1), based on the binary compounds ScCu and ScAl with CsCl-type structure (cP2, Pm-3m), was established. The investigation of the Ti–Cu–Al system at 800°C confirmed the existence of four ternary compounds: TiCu_0.25Al_2.75 (ZrAl₃, tI16, I4/mmm), TiCu_0.3-0.6Al_2.7-2.4 (Cu₃Au, cP4, Pm-3m), TiCu_2-2.7Al_1-0.3 (MnCu₂Al, cF16, Fm-3m), and TiCu_0.54-1.16Al_l.46-0.84 (MgZn₂, hP12, P6₃/mmc). Electrical resistivity measurements were performed for three compounds in the Sc–Cu–Al system and confirmed metal behavior in the temperature range 5-290 K.

Abstract: A systematic study of samples of nominal composition A₁₄Cu₂₄O₄₁ (A = alkaline-earth metal) with partial replacement on the alkaline-earth metal sites and on the Cu sites was carried out. Layered cuprates of the (Sr,Ca)₂Cu₂O₃-CuO₂ series with partial substitution by Gd, Dy, and Er for Ca were obtained. X-ray powder diffraction analysis indicated that the solubility of the rare-earth metals in the Sr₈Ca₆Cu₂₄O₄₁ compound is limited to 2 atoms per formula unit. The Cu atoms in the structure of the spin-ladder phase can be replaced by Fe, Co, or Ni atoms up to the composition Sr₈Ca₆Cu₂₃Fe₁O₄₁, Sr₈Ca₆Cu₁₈Co₆O₄₁, or Sr₈Ca₆Cu₂₃Ni₁O₄₁, respectively, whereas attempts to replace part of the Cu atoms by Mn or Zn atoms were not successful.

Abstract: This work aims provide an experimental overview of results revealing a unique phenomenon such as non-stochastic changes of the local composition and ordering of the metal-elements within alloys. A necessary and sufficient condition for the occurrence of this phenomenon is the charging with hydrogen the structure of the materials. Interestingly the element distribution changes are observed at room temperature and after a rather long rest time from the initial hydrogen insertion. The changes of positions and environments of the elements yield changes in phase compositions. This effect was observed in both amorphous and crystallized compounds, here we will report on the first category of materials, in particular Finemet alloys. The phenomenon was investigated using various experimental techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM).

Abstract: Experimental data on thermionic current density and electron work function of YB₁₂ (100) at T = 1218 – 1978 K in high vacuum (p < 10^-4 Pa) are first introduced. Temperature dependences of the thermionic current density and effective electron work function are presented without extrapolation to the zero-field currents because of the anomalous Schottky effect. The temperature dependences of theYB₁₂ electron work function can be described by linear functions at certain temperature intervals. Preferential boron evaporation and additional ion bombardment by the residual gases ions and evaporated boron ions results in appearance of new phases depleted of boron on the YB₁₂ surface. As a result, an YB₄ – YB₆ double layer on the YB₁₂ single crystal surface has formed. The appearance of the new boride phases, depleted of boron, on the emitting surface causes an increase of thermionic current density compared with individual YB₁₂.

Abstract: The crystal structure of the binary compound DyGa₃ at 600°C belongs to the structure type Ta (Rh_0.33Pd_0.67)₃ (Pearson symbol hP40, space group P6₃/mmc: a = 6.1617(3), c = 23.0365(18) Å). Progressive substitution of Ge atoms for Ga atoms in DyGa₃ at 600°C led to the formation of two ternary compounds: DyGa_2.92-2.52Ge_0.08-0.48 (structure type Mg₃In, hR48, R3m, a = 6.1707(3)-6.22374(10), c = 27.7297(15)-28.1185(5) Å) and DyGa_2.32-2.20Ge_0.68-0.80 (PuAl₃, hP24, P6₃/mmc, a = 6.0970(3)-6.1091(6), c = 14.3153(8)-14.3528(14) Å). Both structure types belong to the family of close-packed structures, and the increase of the Ge content in the system DyGa_3-xGe_x is accompanied by a decrease of the hexagonality of the close-packing. Both ternary compounds exhibit metallic type of electrical conductivity.

Abstract: The crystal structure of the new ternary aluminide Sc_1.33Pd₃Al₈ was refined by the Rietveld method from X-ray powder diffraction data. It crystallizes with a Gd_1.33Pt₃Al₈-type structure: hR51-14.00, R-3m, a = 4.29142(4), c = 38.1638(4) Å, R_B = 0.0344. The main feature of the structure is the statistical distribution of Sc atoms and Al₃ triangles within atomic layers of composition Sc₂Al₃ (Sc_0.67Al within the translation unit here), which is likely to correspond to stacking disorder of ordered layers. During the final cycles of the refinement, the occupancies of the corresponding sites were fixed at occ. = 2/3 for Sc in Wyckoff position 6c and occ. = 1/3 for Al in 18h. The unit cell of Sc_1.33Pd₃Al₈ contains six Sc_0.67Al layers, nine Pd and eighteen Al atom layers along the crystallographic direction [001]. Together with the structure types Tb_0.67PdAl₃, Y₂Co₃Ga₉, Sc_0.67Fe₂Si₅, Er₄Pt₉Al₂₄, Yb_0.67Ni₂Al₆, and ErNi₃Al₉, the structure type Gd_1.33Pt₃Al₈ forms a family of intergrowth structures built up of three kinds of similar monoatomic layer.