二聚物X2 和 XK (X= Mn, Fe, Co, Ni, Cu)吸附NO的密度泛函理论研究

为有效降低NO对环境以及人体造成的危害,着重从催化剂入手,研究过渡金属Mn₂, Fe₂, Co₂, Ni₂, Cu₂及K掺杂的MnK, FeK, CoK, NiK, CuK的二聚物对NO的吸附性能.采用密度泛函理论的B3LYP, B3PW91, B3P86, B1B95以及PBE1PBE方法结合LANL2DZ, SDD, CEP-121G基组,采用B3LYP, B3PW91, B3P86以及PBE1PBE方法结合6-31++G(3df, 3pd), 6-311++G(3df, 3pd), 6-31G(d, p), LANL2DZ, SDD基组分别系统研究了X₂和XK (X=Mn, Fe, Co, Ni, Cu)团簇和NO的几何结构,计算出其键长,频率,离解能,再与对应的实验值进行对比.进一步采用PBE1PBE方法结合LANL2DZ和6-31G(d, p)基组研究了X₂NO和KXNO团簇的几何结构,计算出各原子间键长和吸附能.结果表明,...     

Synchrotron X-ray diffraction and absorption studies of CeM2X2 (M=Cu, Ni and X=Si, Ge) at high pressure

The equations of state of CeCu₂Si₂ and CeCu₂Ge₂ to about 60 GPa, as well as that of CeNi₂Ge₂ to 22 GPa and the valence state of Ce in CeCu₂Ge₂ to 20 GPa have been studied at room temperature in a diamond-anvil cell using synchrotron radiation sources. In each compound, the ambient-pressure phase (tetragonal ThCr₂Si₂-type structure) persisted to the highest pressure studied. The unit cell volumes of CeNi₂Ge₂ at ∼5 GPa and CeCu₂Ge₂ at ∼7 GPa, respectively, approached that of CeCu₂Si₂ taken at ambient pressure. From the equation-of-state data, the bulk modulus was derived to be 112.0±5.1 GPa for CeCu₂Si₂, 125.6±4.3 GPa for CeCu₂Ge₂, and 178.4±14.3 GPa for CeNi₂Ge₂. The valence state of Ce in CeCu₂Ge₂ remained trivalent throughout the pressure range investigated.     

Resonance photoelectron spectroscopy of TiX2 (X = S, Se, Te) titanium dichalcogenides

The photoelectron valence band spectra of TiS₂, TiSe₂, and TiTe₂ dichalcogenides are investigated in the Ti 2p-3d resonance regime. Resonance bands in the vicinity of the Fermi energy are found for TiS₂ and TiTe₂. The nature of these bands is analyzed based on model calculations of the density of electronic states in TiS₂, TiSe₂, and TiTe₂ compounds intercalated by titanium atoms. Analysis of experimental data and their comparison with model calculations showed that these bands have different origins. It is found that the resonance enhancement of an additional band observed in TiS₂ is explained by self-intercalation by titanium during the synthesis of this compound. The resonance enhancement in TiTe₂ is caused by occupation of the 3d band in Ti.     

Magnetism and hyperfine interactions in EuM2Ge2 and GdM2Ge2(M = Mn,Fe, Co,Ni, Cu)

X-ray, magnetic susceptibility and ¹⁵¹Eu, ¹⁵⁵Gd Mössbauer effect studies of EuM₂Ge₂ and GdM₂Ge₂ were performed. All compounds crystallize in the ThCr₂Si₂ body centered tetragonal structure. In all compounds, except those with M = Mn and in EuM₂Ge₂, the M component carries no magnetic moment. All compounds except those with Mn are antiferromagnetic at low temperatures. In EuMn₂Ge₂ the Mn moments order ferromagnetically at 330 K and change to antiferromagnetic order when the Eu moments order ferromagnetically (9 K). This behaviour is different from that in GdMn₂Ge₂, where the Mn sublattice orders antiferromagnetically at 365 K and becomes ferromagnetic and antiparallel to the ferromagnetic Gd sublattice at 96 K. The Mössbauer studies of ¹⁵¹Eu and ¹⁵¹Gd provide values for the magnetic hyperfine fields, the quadrupole interactions and the orientation of the magnetic moments relative to the local fourfold axis (c-axis). It turns out that in the Eu compounds the easy axis of magnetization is close to the c-axis, while in the Gd compounds it is in the basal plane. In all systems, excluding those with Mn, the interatomic rare earth-rare earth distances have the dominant effect on the conduction electron charge density and polarization at the rare earth site and on the Curie point.     

X-ray photoelectron spectroscopy of LiM0.05Mn1.95O4 (M = Ni,Fe and Ti)

LiMn₂O₄ and LiM_0.05Mn_1.95O₄ (M = Ni, Fe and Ti) were synthesized by using solid-state reactions and their surface stoichiometries were confirmed by XPS data. The crystal and electronic structures were investigated by using X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). XRD data suggested that LiM_0.05Mn_1.95O₄ possesses nearly no any variations in lattice parameters compared with LiMn₂O₄ for slight substitution of Ni, Fe and Ti; the substituted Ni, Fe and Ti ions were located on the 16d octahedral sites in the spinel crystal lattice. The XPS results suggested that Fe and Ti ions were at + 3 and + 4 oxidation states, respectively; while Ni ions are mixed with + 2 and + 3 oxidation states. The normal oxidation state of Mn ions in the above four materials is almost the same and calculated as + 3.55 according to the splitting energies of Mn3s states.     

Electronic properties of Hf2X intermetallic compounds (X = Al, Si, Ni, Ga and Ge)

Using ¹⁰⁰Pd/¹⁰⁰Rh probes, perturbed angular correlation measurements were performed to study Pd-related defects in Si as a function of dopant concentration and dopant type. Pd-vacancy and Pd-B complexes were identified by their characteristic electric field gradients in highly doped n- and p-type Si, respectively. Both pairs exhibited a T^3/2 temperature dependence of their electric field gradients.     

Penetration depths of superconducting U6X (X = Fe,Co, Mn)

The penetration depths, λ(T), of the heavy-fermion uranium-based superconductors U₆X (X = Fe, Co, Mn) have been measured as a function of temperature at ∼ 35 MHz. It was found that the temperature dependence of λ(T) for these compounds agrees well with the BCS theory. However, the values of λ(0) are large. By comparing the Slater-Pauling curve of the X elements with λ(0)^-1 for the U₆X superconductors, we have found that λ(0)^-1 is proportional to the saturation spin moments of elemental X, suggesting that there is a correlation between the superconductivity of these U₆X superconductors and the magnetic nature of the X elements.     

Magnetic phase transition in Co/Cu/Ni/Cu(100) and Co/Fe/Ni/Cu(100)

Magnetic phase transitions in coupled magnetic sandwiches of Cu/Co/Cu/Ni/Cu(100) and Cu/Co/Fe/Ni/Cu(100) are investigated by photoemission electron microscopy. Element-specific magnetic domains are taken at room temperature to reveal the critical thickness at which the magnetic phase transition occurs. The results show that a coupled magnetic sandwich undergoes three types of magnetic phase transitions depending on the two ferromagnetic films' thickness. A phase diagram is constructed and explained in the process of constructing Monte Carlo simulations, which corroborate the experimental results.     

Heterometallic fullerides of Fe and Cu groups with the composition K2MC60 (M=Fe+2, Fe+3, Co+2, Ni+2, Cu+1, Cu+2, Ag+1)

Heterometallic fullerides with composition K₂MC₆₀, synthesized by exchange chemical reaction of K₅C₆₀ or K₄C₆₀ with chlorides of metals Fe and Cu groups have been investigated by X-ray diffraction, magnetic resonance, Raman and Mössbauer spectroscopy. Magnetization and susceptibility measurements have also been carried out. Metal chlorides from Fe and Cu groups enable to cover the whole range of electronic configuration of metal from d⁵ to d¹⁰. Heterometallic fullerides with M=Cu⁺², Fe⁺², Fe⁺³ and Ni⁺² appeared to be superconductors with T_c=13.9–16.5 K. Ferromagnetism and superconductivity coexist in investigated fulleride K₂Fe⁺³C₆₀.     

Anomalies in the behavior of the non-stoichiometric systems ZrMn2T0.8 (T = Mn,Fe, Co,Ni and Cu)

Unit cell dimensions and hydriding characteristics of the non-stoichiometric systems ZrMn₂T_0.8, with T = Mn, Fe, Co, Ni and Cu have been determined. Hydrides of these systems show plateau pressures at 25 C which vary in a systematic way with the atomic number of T, ranging from 0.3 (for T = Fe) to 4 atm (for T = Co). All of these plateau pressures are much greater than that of the hydride of stoichiometric ZrMn₂. There is a “Cobalt Effect” in that the plateau pressure of ZrMn₂Co_0.8 hydride is extraordinarily high and, moreover, the lattice dimensions of ZrMn₂Co_0.8 are small compared to ZrMn₂ and the other ternaries. The origin of the Co effect is as yet unclear. It may originate with the particulars of the site occupancies or special metallic bonding effects.     

Structural and magnetic properties of RET2Sn2 compounds (RE=La,Ce, Sm; T=Ni,Cu)

The following compounds have been synthesized: LaCu₂Sn₂, CeCu₂Sn₂, SmCu₂Sn₂ and SmNi₂Sn₂. By means of X-ray diffraction their structure was determined to be primitive tetragonal of CaBe₂Ge₂-type (space group P4/nmm) and the lattice parameters were obtained.¹¹⁹Sn Mössbauer measurements were performed in a temperature range between 4.2 K and 300 K. The temperature dependence of the Lamb-Mössbauer factor reveals considerable softening of lattice vibration modes below 160 K. Only SmCu₂Sn₂ orders magnetically above 4.2 K.     

Quantum mechanically guided design of Co43Fe20Ta(5.5)X(31.5) (X=B, Si, P, S) metallic glasses

A systematic ab initio molecular dynamics study was carried out to identify valence electron concentration and size induced changes on structure, elastic and magnetic properties for Co(43)Fe(20)Ta(5.5)X(31.5) (X=B, Si, P, S). Short range order, charge transfer and the bonding nature are analyzed by means of density of states, Bader decomposition and pair distribution function analysis. A clear trend of a decrease in density and bulk modulus as well as a weaker cohesion was observed as the valence electron concentration is increased by replacing B with Si and further with P and S. These changes may be understood based on increased interatomic distances, variations in coordination numbers and the electronic structure changes; as the valence electron concentration of X is increased the X bonding becomes more ionic, which disrupts the overall metallic interactions, leading to lower cohesion and stiffness. The highest magnetic moments for the transition metals are identified for X=S, despite the fact that the presence of X generally reduces the magnetic moment of Co. Furthermore, this study reveals an extended diagonal relationship between B and P within these amorphous alloys. Based on quantum mechanical data we identify composition induced changes in short range order, charge transfer and bonding nature and link them to density, elasticity and magnetism. The interplay between transition metal d band filling and s-d hybridization was identified to be a key materials design criterion.     

The spin-dependent transport properties of endohedral transition-metal-fullerene X@C66H4 (X=Fe,Co, Mn,Ni)

Inspired by recent experiments on the successful synthesis of hydrofullerene C₆₆H₄ in Tian et al. (2019) [12] with two negatively curved heptagons. Based on the density functional theory and nonequilibrium Green's function method, we report the spin-dependent transport through transition-metal-atom-encapsulated C₆₆H₄ hydrofullerene, i.e., X@C₆₆H₄(X=Fe, Co, Mn, Ni), contacted by single gold atoms via semi-infinite non-magnetic Au electrodes. It is found that, Mn- and Fe-doped systems show highly spin-polarized transmission as well as considerable magnetic moments whereas Ni-doped systems show completely spin-unpolarized transmission and nonmagnetic. Interestingly, Co-doped systems show two spin states, i.e., spin-polarized and spin-unpolarized ones. Further analysis shows that, for Mn-, Fe- and Ni-doped systems, the spin-polarized/unpolarized state is caused by the finite/(nearly-)zero magnetism of the encapsulated metal atom. While the magnetism in Co-doped systems is quenched for the top hexagonal doping case, but not for the side heptagonal doping one, which induces the spin-unpolarized/spin-polarized state. And the screening effect of electrodes on the magnetism of Co is the underlying physical mechanism. Our findings would be beneficial to the design of spintronics devices.     

Nonreciprocal light birefringence in the R 3B7O13 X Boracites (R=Co, Cu, Ni; X=I, Br)

The field and angular dependences of nonreciprocal birefringence (NB), which is linear in magnetic field B and is due to magnetic-field-induced spatial dispersion, have been studied in the cubic (symmetry class T _d) paraelectric phase of the R ₃B₇O₁₃ X boracites (R=Co, Cu, Ni; X=I, Br) at a wavelength λ=633 nm. It is shown that the NB in crystals with different 3d and halogen ions exhibits the same anisotropy. The relation between the A and g parameters, A=2g, which determine the NB anisotropy, suggests that the microscopic mechanism of the NB is the manifestation of second-order magnetoelectric susceptibility at optical frequencies.     

Ab-initio investigation of electronic properties and magnetism of half-Heusler alloys XCrAl (X=Fe, Co, Ni) and NiCrZ (Z=Al, Ga, In)

The electronic structures and magnetism of the half-Heusler alloys XCrAl (X=Fe, Co, Ni) and NiCrZ (Z=Al, Ga, In) have been investigated to search for new candidate half-metallic materials. Here, we predict that NiCrAl, and NiCrGa and NiCrIn are possible half-metals with an energy gap in the minority spin and a completely spin polarization at the Fermi level. The energy gap can be attributed to the covalent hybridization between the d states of the Ni and Cr atoms, which leads to the formation of bonding and antibonding peaks with a gap in between them. Their total magnetic moments are 1μ_B per unit cell; agree with the Slater-Pauling rule. The partial moment of Cr is largest in NiCrZ alloys and moments of Ni and Al are in antiferromagnetic alignment with Cr. Meanwhile, it is also found that FeCrAl is a normal ferromagnetic metal with a magnetic moment of 0.25μ_B per unit cell and CoCrAl is a semi-metal and non-magnetic.     

混合团簇Cu12A(A=Fe、Co、Ni)结构及能量特性的密度泛函研究

以Cu13非紧致低对称性基态结构及四种13原子高对称性(Ih、Oh、D5h、D3h)密堆积结构为初始构型,通过不等价位原子替换,利用密度泛函理论系统研究了Cu12A (A=Fe、Co、Ni)混合团簇的结构及能量特性.结果表明:Cu12 A(A=Fe、Co)团簇的基态结构均以Ih替换结构为主,且均倾向于中心位置替代的高对称性结构,而Cu12Ni团簇基态则为与Cu13类似的非紧致低对称性结构;Fe、Co、Ni三者对Cu13基态各不等价位替代结构稳定性序列基本相同,而对四种高对称性结构相应中心替代构型稳定性均高于表面替代构型(且Fe、Co均明显强于Ni);对各混合团簇基态结构均无明显同分异构现象.