点缺陷对 L12-Al3Li金属间化合物热力学性能的影响

运用基于第一性原理的平面波赝势法研究了L12-Al3Li金属间化合物中Li原子空位和Al原子反位缺陷对Al3Li热力学性能的影响,结果表明：Al反位缺陷易与周围原子形成局域共价键,使晶体体积增大,而Li空位缺陷却减小了晶体体积。Li空位缺陷使L12-Al3Li的硬度增加,延展性降低,德拜温度值升高。Al反位缺陷降低了晶体的硬度,增加了延展性,降低了德拜温度值。在德拜温度以下,Li空位缺陷减小了L12-Al3Li的热容, 而Al反位缺陷使晶体热容增大。晶格畸变对L12-Al3Li晶体的热力学性能有重要影响     

Synthesis and structural characterization of A3In2Ge4 and A5In3Ge6 (A=Ca, Sr, Eu, Yb)—New intermetallic compounds with complex structures, exhibiting Ge-Ge and In-In bonding

Reported are the synthesis and the structural characterization of four new polar intermetallic phases, which exist only with mixed alkaline-earth and rare-earth metal cations in narrow homogeneity ranges. (Sr_1-xCa_x)₅In₃Ge₆ and (Eu_1-xYb_x)₅In₃Ge₆ (x≈0.7) crystallize in the orthorhombic space group Pnma with two formula units per unit cell (own structure type, Pearson symbol oP56). The lattice parameters are as follows: a=13.109(3)-13.266(3) Å, b=4.4089(9)-4.4703(12) Å, and c=23.316(5)-23.557(6) Å. (Sr_1-xCa_x)₃In₂Ge₄ and (Sr_1-xYb_x)₃In₂Ge₄ (x≈0.4-0.5) adopt another novel monoclinic structure-type (space group C2/m, Z=4, Pearson symbol mS36) with lattice parameters in the range a=19.978(2)-20.202(2) Å, b=4.5287(5)-4.5664(5) Å, c=10.3295(12)-10.3447(10) Å, and β=98.214(2)-98.470(2)°, depending on the metal cations and their ratio. The polyanionic sub-structures in both cases are based on chains of InGe₄ corner-shared tetrahedra. The A₅In₃Ge₆ structure (A=Sr/Ca or Sr/Yb) also features Ge₄ tetramers, and isolated In atoms in nearly square-planar environment, while the A₃In₂Ge₄ structure (A=Sr/Ca or Eu/Yb) contains zig-zag chains of In and Ge strings with intricate topology of cis- and trans-bonds. The experimental results have been complemented by tight-binding linear muffin-tin orbital (LMTO) band structure calculations.     

Chemical bonding in equiatomic cerium intermetallics – The case of CeMgSn,CePdSn, and CeMgPb

The electronic and magnetic structures and the properties of chemical bonding in isopointal CeMgSn and CePdSn (both phases belong to the family of TiNiSi related intermetallics, space group Pnma) and CeMgPb belonging to the family of CeScSi intermetallics, space group I4/mmm, have been investigated within the density functional theory (DFT). The charge analyses indicate negatively charged tin and lead leading to assign the compounds as stannides and plumbides, as also illustrated by the mapping of the electron localization function ELF. Calculations within spin-degenerate non-magnetic spin-polarized ferro- (SP-F) and SP-antiferromagnetic configurations led to assign a major role of Ce 4f states in the onset of ordered moments within SP-AF ground states from energy differences. Chemical bonding analyses from crystal orbital overlap populations revealed the strongest interactions for Ce–Sn in CeMgSn, Ce–Pb in CeMgPb, and Ce–Pd in CePdSn.     

27Al NMR study in ZrNiAl

We have studied the microscopic properties of the hexagonal ZrNiAl, a model compound for a wide family of intermetallic compounds crystallizing in this type of structure, by using ²⁷Al NMR spectroscopy. We have investigated the lineshape of static and MAS NMR spectra as a function of magnetic field strength (4.7–9.4 T) and temperature (5–300 K). Our data indicate that the ²⁷Al NMR spectra result from a combined effect of quadrupole and anisotropic shift interactions. The ²⁷Al nuclei are in an environment characterized by the quadrupole coupling constant e²qQ/h of 3.3 MHz, asymmetry parameter η_Q of 0.42, isotropic shift δ_iso of 393 ppm, shift anisotropy δ_anis = δ_zz − (δ_xx + δ_yy)/2 of 150 ppm, and asymmetry factor η_S of 0.5. They are found to be temperature independent. The spin–lattice relaxation rate measured at 7.05 T is proportional to the temperature with T₁T = 135 s K. The mechanisms responsible for observed values of δ_iso, δ_anis, T₁T, and the enhanced Korringa constant are discussed.     

Half-metallicity in the full-Heusler Co2ScP compound: A density functional study

The electronic structure and magnetic properties of the Heusler compound Co₂ScP have been investigated by the generalized gradient approximation based on density functional theory. The results show that the ground state phase of the Co₂ScP compound possesses AlCu₂Mn-type crystal structure and exhibits half-metallic ferrimagnetism. The total spin moment is 2 μ_B at the equilibrium lattice constant a₀=5.83 Å, which agrees with the Slater–Pauling rule. The spin-up electrons are metallic, but the spin-down bands are semiconductor with a gap of 0.55 eV, and the spin-flip gap is of 0.07 eV.     

Non-Fermi liquid behavior in polycrystalline Ce2PdIn8

We report on the formation of a novel ternary compound Ce₂PdIn₈ that is isostructural with the heavy-fermion superconductors Ce₂CoIn₈ and Ce₂RhIn₈. Its magnetic, electrical transport and thermodynamic properties were studied on polycrystalline samples in wide ranges of temperature and magnetic field strength. The results revealed Ce₂PdIn₈ to be a paramagnetic Kondo lattice with a coherence temperature of about 12 K. The C/T ratio of the specific heat reaches at 350 mK a strongly enhanced magnitude of about per Ce-atom, thus clearly indicating a heavy-fermion nature of this material. Moreover, a logarithmic divergence of C/T vs. T, observed below 3 K, which is accompanied by a linear temperature dependence of the electrical resistivity below 6 K, hint at a non-Fermi liquid character of the electronic ground state in the new compound reported.     

Magnetic anisotropy of UFe6Al6

A comparative study of magnetization in UFe₆Al₆ and LuFe₆Al₆ single crystals gives clear evidence for the magnetic state of uranium in UFe₆Al₆. Both compounds exhibit the easy-plane type of magnetic anisotropy, however, the anisotropy energy in UFe₆Al₆, characterized by the anisotropy constants K₁=−7.3 MJ m⁻³ and K₂=−1.25 MJ m⁻³ at 2 K, exceeds by an order of magnitude that in LuFe₆Al₆. Anisotropy within the easy plane in the ferromagnetic state and anisotropy in the paramagnetic range, both absent in LuFe₆Al₆, are observed in UFe₆Al₆.     

Syntheses and Crystal Structure Characterizations of New Rare Earth Nickel Bismuth Compounds RNixBi2 (R = Y, Gd Tb and Dy)

1 INTRODUCTION In recent decades, the ternary systems of rare earth (R)-transition metal (T)-pnictogen (M) show rich chemistry and have attracted wide interest[1] because of their unusual physical properties, such as heavy Fermion, thermoelectric transformation, etc[2]. Although some antimonide phases have been re- ported[3, 4], bismuthide systems have been less inves- tigated up to now. In comparison with antimony systems, rich compounds in bismuth systems are also expected to be disco…     

TiAl基金属间化合物的摩擦学研究进展

本文综述了Ti Al基金属间化合物的摩擦学性能研究以及提高其摩擦学性能所采用的方法,旨在对Ti Al基合金的摩擦磨损特性和现有研究水平有一个系统全面的认识,并在此基础上展望未来Ti Al基金属间化合物摩擦学研究的发展趋势和方向.