Crystal structure and Rietveld refinement of the new ternary compound Al14Nd5Si

The new ternary compound Al14Nd5Si has been studied by means of the X-ray powder diffraction technique and the Rietveld method. The ternary compound Al14Nd5Si has a hexagonal Ni3Sn-type structure with space group P63/mmc (No.194), the lattice parameters are a = 0.64470 (2) nm and c = 0.45926 (1) nm. The Smith and Snyder figure of merit for the index, FN, is F30 = 97.8 (30). The X-ray diffraction data indicated that the crystal structure of the compound Al14Nd5Si has been successfully refined by the Rietveld method. The R-factors of Riet- veld refinement are Rp = 0.088 and Rwp = 0.120, respectively. The thermal dependence of magnetization for the compound was measured by a vibrating sample magnetometer. The experimentally determined magnetic effective paramagnetic moment is μeff = 3.60 μB per Nd atom. The paramagnetic Currie temperature θp = -33.7 K was also obtained from the Currie-Weiss law.     

New ternary compound LasAl13Sn3

A new ternary compound LasAl13Sn3 was synthesized and studied by means of X-ray powder diffraction technique. The compound La8Al13Sn3 crystallizes in a hexagonal AlB2-type structure with space group P6/mmm (No. 191) and the lattice parameters a = 0.44919(1) nm and c = 0.43835(1)nm. The Smith and Snyder figure of merit for index, FN, is F30 = 197.3(30). The Rietveld refinement for the crystal struc-ture of the compound was carried out successfully. The liability R-factors of Rietveld refinement are Rp = 0.114 and Rwp = 0.148. The com-pound La8Al<13>Sn3 decomposes into LaAl2 with cubic Structure and space group Fd3m (227), LaAl3 with hexagonal structure and space group P63/mmc (194), and Sn at 720℃.     

New ternary compound La<Subscript>8</Subscript>Al<Subscript>13</Subscript>Sn<Subscript>3</Subscript>

A new ternary compound La₈Al₁₃Sn₃ was synthesized and studied by means of X-ray powder diffraction technique. The compound La₈Al₁₃Sn₃ crystallizes in a hexagonal AlB₂-type structure with space group P6/mmm (No. 191) and the lattice parameters a = 0.44919(1) nm and c = 0.43835(1) nm. The Smith and Snyder figure of merit for index, F _N , is F ₃₀ = 197.3(30). The Rietveld refinement for the crystal structure of the compound was carried out successfully. The liability R-factors of Rietveld refinement are R _p = 0.114 and R _wp = 0.148. The compound La₈Al₁₃Sn₃ decomposes into LaAl₂ with cubic structure and space group Fd $ bar 3 $ bar 3 m (227), LaAl₃ with hexagonal structure and space group P6₃/mmc (194), and Sn at 720°C.     

A new ternary compound YbZn2As2 with mixed valency of Yb

A new compound with chemical formula YbZn₂As₂ and ‘anti’-La₂O₃-type crystal structure (space group P3m1) has been synthesized for the first time. The trigonal lattice constants of the compound are a=0.4157 and c=0.6954 nm. In the temperature range 77–500 K, the magnetic susceptibility of YbZn₂As₂ follows the Curie–Weiss law, indicating antiferromagnetic interactions of the Yb ions and yielding a Curie temperature θ=−52.8 K and an effective magnetic moment μ_eff=2.35 μ_B (the Bohr magneton) per Yb ion. This means that a part of the Yb ions has valency 3+, instead of 2+ for all the Yb ions, as would be expected from their formal oxidation number, i.e. YbZn₂As₂ is a compound with mixed valency of Yb. YbZn₂As₂ exhibits p-type conductivity with a room temperature electrical resistivity of 0.15 Ω cm which decreases when lowering temperature and reaches a practically constant value of 0.08 Ω cm below 20 K.     

Crystal structural refinement of the new compound TmAlB14

Single crystals of the new phase TmAlB₁₄ were grown using the high-temperature solution method. The crystal structure of TmAlB₁₄ was refined from X-ray powder diffraction data using the Rietveld method. The structure is of MgAlB₁₄-type with the space group Imma and unit cell parameters a = 5.8212(3) Å, B = 10.3837(2) Å and C = 8.1762(3) Å. The final, conventional R-valve and profile R-value are 0.031 and 0.064, respectively. The structure is characterized by a partial occupancy of both metal positions and a splitting of the thulium atomic position.     

Crystal structure and magnetism of the Y2Pd14B5 compound

The crystal structure of the ternary boride Y₂Pd₁₄B₅, space group I4₁/amd, a=8.484(2) Å, c=16.490(3) Å, V=1186.98 ų, Z=4, was refined down to R=0.0475, wR2=0.1276 from single crystal X-ray diffraction data. Two types of coordination for boron atoms were observed: the coordination sphere for the B1 atom is a trigonal prism with one additional atom; the B2 atom has only four neighboring atoms which form a square. No boron–boron contact was observed. Analysis of the Y₂Pd₁₄B₅ crystal structure shows the existence of a correlation between this structure and the Sc₄Ni₂₉B₁₀ structure type. Magnetization and AC susceptibility measurements indicate that there is no superconducting or magnetic transition in Y₂Pd₁₄B₅ down to 2 K.     

Crystal structure, thermal expansion and magnetic properties of new compound Dy1.2Fe4Si9.8

The new ternary compound Dy_1.2Fe₄Si_9.8 have been prepared and studied by means of X-ray powder diffraction technique and vibrating sample magnetometer. The ternary compound Dy_1.2Fe₄Si_9.8 crystallizes in the hexagonal Er_1.2Fe₄Si_9.8-type structure, space group P6₃/mmc (no. 194) with lattice parameters a = 0.39415(1) nm and c = 1.52771(3) nm. The crystal structural refinement of the compound Dy_1.2Fe₄Si_9.8 has been performed by using Rietveld method. Lattice thermal expansion studies on the compound were carried out in the temperature range from 298 to 1013 K. The variation of the unit cell parameters shows that the unit cell parameters increase with the increase in temperature. The coefficients of average lattice thermal expansion along various axes in the temperature range from 298 to 1013 K are , and . The temperature dependence of the magnetization for the compound was also investigated in the range from 90 to 300 K. The experimentally determined magnetic effective paramagnetic moment is μ_eff = 11.3μ_B per formula unit (10.3μ_B per Dy atom).     

Crystal structures of new ternary rare earth silicides Sc3Pr2Si4, Sc1.26Pr3.74Si4 and Sc3.96Nd1.04Si4 with ordered and partially ordered rare earth sites

The crystal structures of three new ternary silicides Sc₃Pr₂Si₄, Sc_1.26Pr_3.74Si₄ and Sc_3.96Nd_1.04Si₄ were determined by single crystal X-ray diffraction. The title compounds crystallize with three different substitution derivatives of the Sm₅Ge₄ structure type (orthorhombic space group Pnma) containing various distributions of rare earth atoms on the three Sm sites. Crystal chemistry analysis shows that these distributions are controlled by the atomic size factor.     

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 of Zr9Co7In14

Zr₉Co₇In₁₄ crystallizes in the cubic system, space group Fm3m, a = 13.300(2) Å Z = 2, R = 0.0412 for 567 unique reflection (KM-4 diffractometer, Mo K radiation). The crystal structure, related to the Cr₂₄C₆ -type structure, can be described as a stacking of columns of cubes, tetragonal antiprisms, and cubo-octahedrons extending along the coordinate axes. One of the ln atoms is coordinated by a Frank-Kasper polyhedron.     

Ce2Ir5B2, a new structure type of ternary borides

The crystal structure of a new ternary boride Ce₂Ir₅B₂, space group , a=5.477(2) Å, c=31.518(5) Å, Z=6, V=818.79 Å, was refined down to R=0.0484, wR₂=0.1211 from single crystal X-ray diffraction data. This is the first representative of a new structure type of intermetallic compounds (an ordered variant of the binary Er₂Co₇ compound). The structure of Ce₂Ir₅B₂ is the stacking variant of the MgCu₂- and CeCo₃B₂-type slabs and belongs to the structural series with the general formula R_2+nM_4+3nX_2n (n=2).     

Crystal structure and properties of the new ternary compound Mg21Ga5Hg3

The crystal structure of a new ternary compound Mg₂₁Ga₅Hg₃ has been studied using X-ray powder diffraction data by Rietveld method. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDXS) was used for sample composition examination. The compound crystallizes in the Ge₈Pd₂₁ structure type (space group I4₁/a, a = 1.45391(5) nm, c = 1.15955(4) nm, Z = 4). All interatomic distances indicate metallic type bonding. The average thermal expansion coefficients α_a, α_c and α_V of Mg₂₁Ga₅Hg₃ are 2.60 × 10^?5 K^?1, 2.02 × 10^?5 K^?1, and 7.25 × 10^?5 K^?1, respectively. Electrical resistivity of Mg₂₁Ga₅Hg₃ was measured between 5 and 300 K.     

The crystal structure of the novel ternary silicide Sm4Pd4Si3

The crystal structure of the compound Sm₄Pd₄Si₃ was determined by the single-crystal method (KM-4 automatic diffractometer, Mo K radiation. Sm₄Pd₄Si₄ has the monoclinic Nd₄Rh₄Ge, type structure: space C2/c, mC44 (No. 15). a = 20.693(6), B = 5.584(1), C = 7.699(2) Å, β = 109.48(3)°, V = 838 Å, Z = 4, μ - 36.23 mm¹, R =_F = 0.0537, R _F = 0.0435 for 1652 unique reflections. The coordination numbers of samarium atoms are 17 and 18. For palladium and silicon atoms icosahedra and trigonal prisms with additional atoms are typical as coordination polyhedra. The structure of Sm₄Pd₄Si₄ is composed of fragments of the YPd₂Si and Y₁Rh₂Si₂ structure in a ratio 1:1.     

Effect of rare earth Pr on microstructure and mechanical properties of Al2O3-SiO2（sf）/Al-Si composites

The Al₂O₃-SiO₂(sf) (volume fraction, 20%)/Al-12.6Si metal matrix composites(MMCs) with or without rare earth Pr addition were fabricated by infiltration squeeze method. Effect of Pr addition on microstructures and fractographs of Al-Si MMCs was investigated by SEM and TEM. Tensile properties at room temperature and 200 °C were tested. It is shown that the addition of Pr is favorable to produce uniform microstructures and modify the eutectic Si crystal effectively. Compounds/intermetallics with high content of Pr are formed at the interface between short fiber and matrix. Yield strength(σ_0.2), ultimate tensile strength(σ_b) and fracture elongation of Al-Si MMCs are improved by adding suitable amount of Pr. Compared with those values of Al-Si based MMC at 200 °C, σ_0.2 and σ_b of MMC with 0.29% Pr are increased by 33% and 55%, respectively. The tensile fracture surface of Al-Si MMCs with Pr addition presents ductile fracture features.     

Reactive synthesis of porous Cu3Si compound

Cu₃Si compounds have lots of wonderful applications such as synthesizing nanostructured materials. Here we synthesized a Cu₃Si compound with novel porous microstructure via Cu/Si reaction. The elevated temperature reaction between copper and silicon was not only used to generate Cu₃Si compound, but was also employed to form porous microstructure. The obtained porous compound is mainly composed of Cu₃Si phase, and the size of dispersed micropores varies about 10-150 μm by changing the silicon content in Cu/Si green compact. Moreover, the porous compound exhibits very low thermal diffusivity. It is believed that during being synthesized at 900 °C, the compact transforms to Cu₃Si compound, while a quantity of liquid Cu₃Si phase separates from compact and generates tiny particles on its surface, so forms porous microstructure.     

Magnetic properties and magnetic structure of the Mn5Si3-type Tb5Si3 compound

Neutron diffraction and magnetization measurements have been performed on the Tb₅Si₃ compound (hexagonal Mn₅Si₃-type, hP16, P6₃/mcm) to understand its magnetic structure and magnetic properties. The temperature-dependent neutron diffraction results prove that this intermetallic phase shows a complex flat spiral magnetic ordering, presenting three subsequent changes in magnetization at on cooling. However, the magnetization data depict two transitions at 72 K (T_N1) and 55 K (T_N2). The extended temperature range between and over which the neutron diffraction patterns slowly evolve might correspond to the high-temperature antiferromagnetic transition at T_N1 and low-temperature antiferromagnetic transition at T_N2 of the magnetic data. Between Tb₅Si₃ shows a flat spiral antiferromagnetic ordering with a propagation vector K₁ = [0,0, ±1/4]; then, between the flat spiral type ordering is conserved, but by two coexisting propagation vectors K₁ = [0,0, ±1/4] and K₂ = [0,0, ±0.4644(3)]. The terbium magnetic moments arrange in the XY(ab) plane of the unit cell. Below the magnetic component with K₁ = [0,0, ±1/4] vanishes and magnetic structure of Tb₅Si₃ is a flat spiral with K₂ = [0,0, ±0.4644(3)], only. Low field magnetization measurements confirm the occurrence of complex, multiple magnetic transitions. The field dependence of the magnetization indicates a metamagnetic transition at a critical field of 3 T.     

Electronic structure and thermoelectric power of CeNi4Si

The studies of the thermoelectric power and band structure calculations for CeNi₄Si are reported. These studied are supported by magnetic susceptibility, electrical resistivity, specific heat and X-ray photoemission spectroscopy measurements. CeNi₄Si is paramagnetic down to 2 K and follows the Curie–Weiss law with μ_eff = 0.52μ_B/f.u. and the paramagnetic Curie temperature θ_P = −2 K. This effective paramagnetic moment is lower than the free Ce³⁺ value. The obtained values for the f occupancy n_f and for the coupling Δ of the f level with the conduction states are in good agreement with the values found for mixed valence compounds. Below the Fermi energy the total density of states contains mainly the d states of Ni atoms. The narrow peaks of the f states of Ce atoms were found above the Fermi level. CeNi₄Si is characterized by γ = 16 mJ mol⁻¹ K⁻² and θ_D = 335 K.     

Investigation of the electronic structure of the new quaternary hydride PdSr2LiH5

We have investigated the band structure of the new tetragonal quaternary mixed alkali-alkaline earth transition metal hydride PdSr₂LiH₅ by means of the ab initio augmented plane wave method. We find this material to be metallic. The total density of states as well as its partial wave analysis have been used to investigate the origin of the electronic states. In this hydride, like in superconducting PdH, the palladium d bands are essentially filled and the H-s states have a non-negligible contribution at the Fermi energy. We find the electronic contribution to the electron-optical phonon coupling constant to be sizeable, although smaller than in PdH.     

Crystal structure and electrochemical behaviors of Pt/mischmetal film electrodes

The Ml(La-rich mischmetal0films with a thin Pt layer on the substrate of chemically coarse ITO glass or silicon slices were prepared by magnetic sputtering tchnique.The crystal structure and surface morphology of the films were investigated by X-ray diffraction(XRD)analysis and atomic force microscopy(AFM),respectively, The electrochemical hydridation/dehydridation behaviors of the films in KOH solution were studied by using cyclic voltammagraph and electrochemical impedance spectrum(EIS)as well.The AFM results show that the Pt cover layer on the M1 films is of island structure with a grain of 150-200nm in size.The presence of a thin Pt layer can provide sufficient high electrocatalytic activity for the electrochemical charge-transfer reaction.The electrochemical reduction and oxidation reaction occur on the Pt layer,and the diffusion of H into the Ml film is the rate-controlled step.The Pt coatings also act as protective layers,preventing oxidation and/or poisoning of the underlying Ml films in air.