Determination of the structure of UFe2Al10 compound

The atomic structure of a new ternary phase UFe₂Al₁₀ appearing in the U–Fe–Al system was determined using direct methods applied to X-ray powder diffraction data. High resolution electron microscopy combined with the methods of crystallographic image processing was used for the verification of the structural model. The UFe₂Al₁₀ phase is orthorhombic and belongs to Cmcm space group, its unit cell contains 40 Al, eight Fe, and four U atoms. The lattice parameters obtained after Rietveld refinement are: a=8.919 Å, b=10.208 Å, and c=9.018 Å. The reliability factors characterizing the Rietveld refinement procedure are: R_p=5.9%, R_wp=8.1%, and R_b=2.9%.     

Crystal structure, thermal expansion and electrical properties of the new Al0.32ErGe2 compound

A new ternary compound Al_0.32ErGe₂ has been synthesized and studied from 298 K to 773 K using X-ray powder diffraction technique. Its structure has been determined at room temperature by Rietveld refinement of X-ray powder diffraction data. The ternary compound Al_0.32ErGe₂ crystallizes in the orthorhombic with the defect CeNiSi₂ structure type (space group Cmcm, a = 0.40701(2) nm, b = 1.60401(9) nm, c = 0.39240(2) nm, Z = 4 and D_calc = 8.326 g/cm³). The average thermal expansion coefficients , and of Al_0.32ErGe₂ are 1.72 × 10⁻⁵ K⁻¹, 1.11 × 10⁻⁵ K⁻¹ and 1.52 × 10⁻⁵ K⁻¹, respectively. The bulk thermal expansion coefficient is 4.35 × 10⁻⁵ K⁻¹. Electrical resistivity of Al_0.32ErGe₂ was measured between 5 K and 300 K.     

Crystal structure and magnetic properties of ZnV2O4

We present structural and magnetic data on ZnV₂O₄ single crystals. Single crystal X-ray diffraction shows the measured crystals to be of very high quality, especially with respect to atomic order. The measured magnetic susceptibility resembles to that of a spin glass system, surprising for a translational invariant structure. The results are discussed in the framework of disorder in a magnetically frustrated lattice.     

Growth and annealing properties of Mg0.4Al2.4O4 crystal

Mg_0.4Al_2.4O₄ single crystals with good optical quality were successfully grown by the Czochralski method. The transmission spectrum indicated that the absorption edge of the crystal was at 220 nm, while no apparent absorption peaks were found. The X-ray diffraction and DSC curve analysis showed that Mg_0.4Al_2.4O₄ crystal was stable at room temperature. While after annealing in the air and hydrogen atmosphere at about 1200 °C, Mg_0.4Al_2.4O₄ decomposed into Al₂O₃ and (MgO)_0.4(Al₂O₃)_x (0.4 < x < 1.2). The reaction mainly occurred on the crystal surface, barely inside.     

Crystal structure and magnetic properties of the binary uranium–nickel alloy U11Ni16

The crystal structure of the U–Ni binary compound previously designated U₅Ni₇ was studied by X-ray single crystal diffraction showing that the exact formula is U₁₁Ni₁₆. Uranium and nickel atoms are distributed respectively on 5 and 6 Wyckoff positions of the trigonal space group R (n° 148), and the unit-cell dimensions in the hexagonal setting are: a=11.7786(4) Å, c=20.7485(8) Å. Magnetisation measurements indicate itinerant ferromagnetism below T_c=33 K for U₁₁Ni₁₆.     

Structural, thermodynamic, and electrochemical properties of TixZr1−x(VNiCrMnCoAl)2 C14 Laves phase alloys

The crystal structure of the monoclinic phase η-Al₁₁Cr₂ of the space group C2/c, a ≈ 1.76 nm, b ≈ 3.05 nm, c ≈ 1.76 nm, β ≈ 90° [L.A. Bendersky, R.S. Roth, J.T. Ramon, D. Shechtman, Metall. Trans. A 22A (1991) 5] has been determined by single-crystal X-ray diffraction. The structure model, refined to a final R value of 0.0441, has the composition of Al_83.8Cr_16.2. a = 1.77348(10) nm, b = 3.04555(17) nm, c = 1.77344(10) nm, monoclinic angle β = 91.0520(12)°. There are 80 (66Al + 14Cr) independent atomic positions in a unit cell, of which all Cr atom sites and 8 Al atom sites have icosahedral coordination. These icosahedra are interconnected forming icosahedral chains along , (1 0 1) icosahedral layer blocks as well as a three-dimensional icosahedral structure.     

Single crystal preparation and crystal structure of the Cu2Zn/Cd,Hg/SnSe4 compounds

Single crystals of Cu₂Zn/Cd/SnSe₄ were grown using a solution-fusion method. The crystal structure of the Cu₂Zn/Cd,Hg/SnSe₄ compounds were investigated using X-ray powder diffraction. These compounds crystallize in the stannite structure (space group I 2m) with the lattice parameters: a=0.56882(9), c=1.13378(9) nm, c/a=1.993 (Cu₂ZnSnSe₄), a=0.58337(2), c=1.14039(4) nm, c/a=1.955 (Cu₂CdSnSe₄) and a=0.58288(1), c=1.14179(2) nm, c/a=1.959 (Cu₂HgSnSe₄). Atomic parameters were refined in the isotropic approximation (R_I=0.0517, R_I=0.0511 and R_I=0.0695 for Cu₂ZnSnSe₄, Cu₂CdSnSe₄ and Cu₂HgSnSe₄, respectively).     

Reactions in the SrH2–Al–H2 system

Five rare-earth R₅CoSb₂ antimonides have been synthesized and characterized by means of X-ray powder diffraction data. The investigated ternary compounds crystallize with orthorhombic ordered substituted variant of the Yb₅Sb₃ structure type (space group Pnma, Pearson symbol oP32). Atomic and thermal parameters have been refined for all intermetallic phases.     

Peculiarities of component interaction in {Gd, Er}-V-Sn Ternary systems at 870 K and crystal structure of RV6Sn6 stannides

The phase equilibria in the Gd-V-Sn and Er-V-Sn ternary systems were studied at 870 K by means of X-ray and metallographic analyses in the whole concentration range. Both Gd-V-Sn and Er-V-Sn systems are characterized by formation of one ternary compound at investigated temperature, with stoichiometry RV₆Sn₆ (SmMn₆Sn₆-type, space group P6/mmm, a = 0.55322(3) nm, c = 0.91949(7) nm for Gd, a = 0.55191(2) nm, c = 0.91869(8) nm for Er). Solubility of the third component in the binary compounds was not observed. Compounds with the SmMn₆Sn₆-type were also found with Dy, Ho, Tm, and Lu, while YV₆Sn₆ compound crystallizes in HfFe₆Ge₆ structure type. All investigated compounds are the first ternary stannides with rare earth elements and vanadium.     

Crystal structure of the Ag2SiS3 compound

The crystal structure of the ternary compound Ag₂SiS₃ was determined on the basis of X-ray powder diffraction. The compound belongs to a new structure type, space group P2₁/c, a = 0.66709(1), b = 0.66567(2), c = 1.31748(3) nm, and β = 118.658(1)°. Ag₂SiS₃ contains isolated [Si₂S₆] anionic units consisting of pairs of edge-shared tetrahedra. The Ag atoms are situated in the interstices formed by these fragments.     

Determination of the structure of a new tetragonal U2FeAl20 phase

The atomic structure of a new ternary U₂FeAl₂₀ phase appearing in the Al-rich corner of a U–Fe–Al system was solved using electron crystallography and X-ray powder diffraction techniques (XRD). The positions of U atoms were determined from crystallographically processed high-resolution electron microscopy (HRTEM) images. These positions were used as a starting set for determining the coordinates of Fe and Al atoms by difference-Fourier synthesis technique. The U₂FeAl₂₀ phase is tetragonal and belongs to the space group. Its unit cell contains 80 Al, 4 Fe, and 8 U atoms. The lattice parameters obtained after Rietveld refinement are: a = 12.4138 Å, c = 10.3014 Å. The reliability factors characterizing the Rietveld refinement procedure are: R_p = 8.65%, R_wp = 11.2% and R_b = 5.93%.     

Crystal structure and magnetic properties of the new ternary actinide compounds AnPd5Al2 (An = U, Np)

We report the crystal structure and magnetic properties of new ternary actinide compounds UPd₅Al₂ and NpPd₅Al₂. Both compounds crystallize in the body-centered tetragonal ZrNi₂Al₅-type tetragonal structure (I 4/mmm). Although the magnetic susceptibility of both compounds follows the Curie–Weiss behavior at high temperature, no magnetic phase transition was observed. UPd₅Al₂ has a nonmagnetic ground state where the magnetic susceptibility saturates at low temperature, while NpPd₅Al₂ superconducts below 4.9 K as reported recently.     

The crystal structure of LiMgAlD6 from combined neutron and synchrotron X-ray powder diffraction

LiMgAlH₆ is the intermediate phase when LiMg(AlH₄)₃ is heated. It contains 9.4 wt.% hydrogen, of which 4.8 wt.% is released during the decomposition step to MgH₂ and LiH. Deuterated LiMgAlD₆ was prepared by heat-treating LiMg(AlD₄)₃ at 130 °C. Powder neutron and synchrotron X-ray diffraction patterns were measured and the structure was refined using the Rietveld technique on both patterns simultaneously. LiMgAlD₆ crystallizes in the trigonal space group P321 with a = 7.9856(4) Å and c = 4.3789(3) Å. The structure consists of isolated AlD₆ octahedra connected through octahedrally coordinated Mg- and Li-atoms.     

Structural and magnetic properties of C15 HoMn2 hydrides

Powder samples of cubic HoMn₂H_x hydrides, with 0 ≤ x ≤ 4.3, have been investigated by X-ray diffraction and AC/DC magnetometry as a function of temperature and external magnetic field. Hydrogen is demonstrated to strongly modify structural and magnetic properties. X-ray studies revealed many structural transformations placed at low temperatures. In particular, a transformation from the cubic to the monoclinic structure was detected, which so far has not been reported for other cubic RMn₂H_x (R - rare earth or Yttrium) compounds. The structural transformations are reflected in the magnetic behavior. The change in ordering temperatures implies a very strong relationship between the magnetic interactions and the Mn-Mn distance modified at hydrogen absorption. Tentative magnetic and structural phase diagrams are proposed. The presented results are compared with the properties of other cubic and hexagonal RMn₂H_x hydrides.     

High temperature transformations of the Au7Cu5Al4 shape-memory alloy

The β-phase of Au₇Cu₅Al₄ undergoes a reversible shape-memory phase transformation, however there has been some uncertainty regarding the crystal structure or structures of the parent phase. Here we show that, under equilibrium conditions, the parent phase possesses the L2₁ structure between its A_p (about 79 °C) and ∼630 °C, and the B2 primitive cubic structure between ∼630 °C and its melting point. It melts directly from B2 into the liquid state and hence never achieves the random bcc A2 structure that has been previously mooted. Splat-cast samples of the alloy are martensitic, proving that development of equilibrium order and defect concentration are not pre-requisites for the A → M transformation to occur.     

Crystal structure of La5Ti4GaO17

The crystal structure of La₅Ti₄GaO₁₇ compound synthesized by heat-treatment of the co-precipitated hydroxy-oxalates has been determined by the X-ray powder diffraction. It was found that crystal structure of La₅Ti₄GaO₁₇ belongs to the CaLa₄Ti₅O₁₇-type structure (space group Pmnn, a = 0.3912(1) nm, b = 3.128(1) nm, c = 0.5523(1) nm, Z = 2). The final R_W value is equal to 0.081 for 169 independent reflections.     

Crystal structures of the Ag4HgGe2S7 and Ag4CdGe2S7 compounds

The crystal structures of the Ag₄HgGe₂S₇ and Ag₄CdGe₂S₇ compounds were investigated using X-ray powder diffraction. These compounds crystallize in the monoclinic Cc space group with the lattice parameters a=1.74546(8), b=0.68093(2), c=1.05342(3) nm, β=93.398(3)° for Ag₄HgGe₂S₇ and a=1.74364(8), b=0.68334(3), c=1.05350(4) nm, β=93.589(3)° for Ag₄CdGe₂S₇. Atomic parameters were refined in the isotropic approximation (R_I=0.0761 and R_I=0.0727, respectively).     

Canted antiferromagnetic structure of HoPtGe2

Neutron powder diffraction has been performed on orthorhombic HoPtGe₂ crystallizing in space group Immm. Lattice constants are a=4.321(3) Å, b=16.344(3) Å, and c=8.731(5) Å. Refined atomic positional parameters are given. A magnetic phase transition from paramagnetism into a canted antiferromagnetic structure occurs at the Néel temperature T_N=8.5 K. The ordered moments at Ho sites 4i and 4h are 8.1 μ_B and 4.0 μ_B at 4.2 K, respectively; the moments are aligned within the ab and bc plane, respectively.