Improving magnetocaloric properties of Fe68–xCrxTb5B23Nb4 (x = 0, 2, 4, 6 and 8) metallic glasses having high glass-forming ability with tunable Curie temperature

Abstract

The impacts of adding Cr on the Curie temperature (T_C), glass-forming ability (GFA), and magnetocaloric effect were studied in Fe_68?xCr_xTb₅B₂₃Nb₄ (x = 0, 2, 4, 6 and 8) metallic glasses prepared by suction casting. GFA depends on Cr content in the composition. For Fe_68?xCr_xTb₅B₂₃Nb₄ bulk metallic glasses (BMGs), with critical diameters up to ~3 mm can be produced by suction casting and maximum value of GFA was found for x = 6. By exchanging Cr with Fe partially, T_C could effectively be adjusted in a quite broad temperature interval from 487 K for x = 0 to 267 K for x = 8, whereas maximum magnetic entropy change decreased from 1.16 to 0.53 Jkg^?1 K^?1 and refrigeration capacity (RC) changed from 116 to 45.05 J/kg under a low field change of 2 T. Though T_C is shifted to room temperature, maximum magnetic entropy change and RC decreased almost half of the base alloy. To enhance these properties (Fe_0.62Cr_0.06Tb_0.05B_0.23Nb_0.04)_100?yCu_y (y = 0.75, 1), metallic glasses are prepared. By the help of small addition of Cu, magnetocaloric properties can be effectively increased without changing the T_C. These findings show that the successful synthesis of the Fe-based Fe₆₂Cr₆Tb₅B₂₃Nb₄ and (Fe_0.62Cr_0.06Tb_0.05B_0.23Nb_0.04)_100?yCu_y (y = 0.75, 1) BMGs near room temperature, could be considered as promising candidates as magnetic refrigerant materials.     

Comparison of O–H and C–H activation of methanol on Ni-based cluster: a DFT investigation

Using the density functional theory, the initial dehydrogenation of methanol on Ni_xM_y (M?=?Ni, Co, Fe, Mn, Cr, x?+?y?=?4, y?=?1, 2) clusters is investigated. Two adsorption and dehydrogenation mechanisms of methanol are studied: one proceeds along the C–H scission and another begins with the breaking of the O-H bond. The adsorption sites of methanol on the Ni or M sites of the Ni_xM_y clusters are considered. The adsorption of methanol on Ni₄ cluster is stronger than those on bimetallic clusters, while the initial dehydrogenation barriers on Ni_xM_y clusters are lower than that on Ni₄ cluster. The comparable energy barriers of two pathways (O–H or C–H dissociation) on Ni-based clusters indicate that these two paths are quite competitive. In addition, the Ni₂M₂ clusters show superior activation performance compared with the Ni₃M clusters, especially for Ni₂Mn₂ and Ni₂Cr₂ clusters. The effects of alloyed metal on the catalytic activity of Ni for methanol initial dehydrogenation, including the adsorption energy, O–H or C–H bond scission barrier and frontier molecular orbital levels, are discussed. It can be concluded that the addition of Co, Fe, Mn and Cr to Ni catalyst is able to enhance the activity of the methanol dehydrogenation reaction.     

Raman scattering and magnetizations studies of (Al, Cr)-codoped 4H-SiC

In this study, the insertion of both Al and Cr atoms into SiC matrix has been experimentally evidenced by X-ray diffraction, Raman scattering, elements analysis and magnetic measurements. Structure analysis showed that (Al, Cr)-codoped SiC has a single-phase 4H-crystal structure and no trace of any other impurity phases were detected. Raman scattering showed that several new features appeared in (Al, Cr)-codoped 4H-SiC: (1) the vanishing of the folded longitudinal-optical phonons modes-plasmon coupling (FLOPC) modes with x=(q/q_B)=0; (2) an obvious absorbing peak was found in Si_1−x−yAl_xCr_yC with y=0.0203 at%; (3) folded transverse-optical (FTO) mode shifts to high frequency and linewidths [full widths at half maximum (FWHM)] decrease with increase in Cr content. Magnetic properties characterizations showed that weak ferromagnetism order is established. With increase in Cr content, the magnetization decreased. No clear influence of Al doping on the magnetic properties of codoped 4H-SiC is evidenced while the magnetic origin should be ascribed to be induced by Cr. It is speculated that doping Cr elements at Si sites destroy the effective coupling of the spins induced by Al doping. The major role of Al is to stabilize the codoped crystal structure as 4H-single-phase.     

Ti1－xCrxO2±δ体系的相关系、晶体结构和磁性能研究

采用溶胶凝胶法制备了Ti_1-xCr_xO_2±δ体系系列样品.利用扫描电子显微镜(SEM)，X射线光电子能谱(XPS)，粉末X射线衍射分析(XRD)方法研究了Ti_1-xCr_xO_2±δ系列样品的颗粒尺寸、形貌、组分化学态、相关系和固溶区范围；并利用超导量子干涉磁强计对样品的磁性能进行了研究.采用Rietveld结构精修的方法研究了Cr的不同掺杂量对TiO₂晶体结构的影响，研究表明，1000℃烧结的样品的固溶区范围是x=0—0.03，为金红石单相；随着Cr掺杂量的增加，金红石相晶胞参数规律性地减小；当x>0.03，为金红石相和CrO₂相两相共存.综合XRD和磁性测量结果，500℃烧结的样品的固溶区范围是x=0—0.02，为锐钛矿单相；随着Cr掺杂量的增加，锐钛矿相晶胞参数规律性地减小；当x≥0.04，为锐钛矿相和绿铬矿相(Cr₂O₃)两相共存.XPS实验结果表明，500℃和1000℃退火的样品中Cr都是以Cr⁺³和Cr⁺⁶两种化学态存在，1000℃烧结的样品中可能有更多的Cr³⁺转化为Cr⁶⁺.根据M-H和M-T曲线的测试结果发现，本文500℃烧结的Ti_1-xCr_xO_2±δ体系样品当x=0—0.02时，为室温铁磁性.当x≥0.04时，由铁磁相和顺磁相所组成，在低温下有较强的铁磁性；室温下主要是顺磁相，铁磁相只占据很小的体积分数. 关键词： 1-xCr_xO_2±δ体系')" href="#">Ti_1-xCr_xO_2±δ体系 相关系 固溶区 磁性能     

Effect of Cr and Ni substitution on the hyperfine parameters of Fe-B based metallic glasses

Some features of the variation of isomer shift, quadrupole splitting and magnetic hyperfine field distribution in Fe_85?xCr_xB₁₅ (x=5–30), Fe_85?yCr₁₅B_y (y=10–20) and Fe_85?xNi_xB₁₅ (x=5–30) metallic glasses are reported. Changes in the isomer shift and quadrupole splitting for the Cr_x and B_y series are linked with a precursor stage for the onset of ferromagnetism.     

Calculated elastic properties of M2AlC (M=Ti, V, Cr, Nb and Ta)

M₂AlC phases, where M is a transition metal, are layered ternary compounds that possess unusual properties. In this paper, we have calculated the elastic properties of M₂AlC, with M=Ti, V, Cr, Nb and Ta, by means of ab initio total energy calculations using the projector augmented-wave method. We have derived the bulk and shear moduli, Young's moduli and Poisson's ratio for ideal polycrystalline M₂AlC aggregates. We have estimated the elastic modulus of Cr₂AlC with 357.7 GPa while the values of all other phases are in the range 309±10 GPa. We suggest that this can be understood based on the calculated bond energies for the M-C bonds. Furthermore, our results indicate a profound elastic anisotropy of M₂AlC even compared to materials with a well-established anisotropic character such as α-alumina. Finally, we have estimated the Debye temperatures of M₂AlC from the average sound velocity.     

铁基Heusler合金Fe2Co1-xCrxSi的结构、磁性和输运性质的研究

基于多种实验手段和能带计算的方法, 对四元合金Fe₂Co_1-xCr_xSi的晶体结构、 磁性、输运性质及能带结构进行了研究. 研究发现, 随着Cr的增加, 合金Fe₂Co_1-xCr_xSi保持了高度有序结构, 逐渐从Hg₂CuTi结构的Fe₂CoSi 过渡到L2₁结构的Fe₂CrSi; 由于次晶格网络的破坏, 居里温度逐渐下降; 系列合金的分子磁矩呈现线性下降, 符合半金属特性; 剩余电阻比率与原子占位有序程度密切相关, 呈现两端大、 中间小的特点. 在Cr替代Co的过程中, 材料半金属能隙逐渐打开, 表现半金属特征. 同时费米能级从Fe₂CoSi半金属能隙的价带顶上移至Fe₂CrSi能隙的导带底. 最大的能隙宽度出现在x= 0.75处, 这表明四元合金有可能成为具有更高自旋极化率和更强抗干扰能力的自旋电子学材料.     

3∶29型Gd3(Fe1-xCox)29-yCry化合物的成相与结构

通过X射线衍射分析和磁测量研究了Gd-Fe-Co-Cr四元系中对应于化学式Gd₃(Fe,Co,Cr)₂₉且Gd含量为一定值的截面内富Fe,Co区的相关系,重点探索了高Co含量3∶29型化合物合成的可能性,研究了3∶29型Gd₃(Fe_1-xCo_x)_29-yCr_y化合物的结构与磁性.研究结果表明,获得3∶29型单相Gd₃(Fe_1-xCo_x)_29-yCr_y化合物的范围为:y=5,0≤x≤0.7;y=5.5,0.7≤x≤0.8和y=6,0.8≤x≤0.9.基于对Gd₃(Fe_1-xCo_x)_29-yCr_y化合物成相条件的研究,成功地合成了纯Co基Gd₃Co_29-yCr_y化合物,其固溶范围为6.5≤y≤7.3.3∶29型单相Gd₃(Fe_1-xCo_x)_29-yCr_y化合物的晶体结构都属于单斜晶系,Nd₃(Fe,Ti)₂₉型结构,空间群为A2m.得到3∶29型单相Gd₃(Fe_1-xCo_x)_29-yCr_y化合物的固溶极限即Co含量的极大值与稳定元素Cr含量有关.Co原子的含量越高,所需稳定元素Cr的含量越大.值得注意的是,用Co原子替代Fe原子会导致Gd₃(Fe_1-xCo_x)_29-yCr_y化合物磁晶各向异性的显著改变.当x≥0.4时,化合物的磁晶各向异性从易面型转变为易轴型 关键词： 3(Fe_1-xCo_x)_29-yCr_y化合物')" href="#">Gd₃(Fe_1-xCo_x)_29-yCr_y化合物 相关系和相结构 X射线衍射 磁晶各向异性     

Microstructure and phase transformations in laser clad CrxSy/Ni coating on H13 steel

Laser cladding was carried out onto H13 steel with preplaced NiCrBSi+Ni/MoS₂ powders using CO₂ laser under the optimized experimental parameters of laser power 2 kW, scanning velocity 6 mm/s and laser beam diameter 3 mm. An X-ray diffractometer and scanning electron microscope with energy dispersive spectroscopy were applied to analyze the microstructure and phase compositions of the coating. Thermodynamic calculation was performed with Thermo-Calc software on the basis of a commercially available Ni-based Alloys׳ database. The experimental results show that MoS₂ decomposed and S reacted with Cr to form nonstoichiometric Cr_xS_y during the laser cladding process. The coating consists of spherical Cr_xS_y particles, primary γ-Ni dendrite, interdendritic eutectic (γ-Ni+NiMo) and precipitated NiMo. The precipitated NiMo was fine and uniformly distributed in primary γ-Ni dendrite. The calculated results and experimental data indicate that the solidification process in the coating during laser cladding process was liquid→liquid+Cr_xS_y→ liquid+Cr_xS_y+γ-Ni→liquid+Cr_xS_y+γ-Ni+ eutectic (γ-Ni+NiMo). A solid state phase transformation (fine and uniformly distributed NiMo precipitated from γ-Ni) occurred after the solidification process. The calculations agree well with the experimental data and it is helpful to understand the phase transformation and microstructure evolution in the coating.     

Cr-Co-Ga Heusler合金新材料探索和物性研究

通过实验和计算研究了从Co₂CrGa到Cr₂CoGa一系列渐变成分合金(Co_50-xCr_x+25Ga₂₅,x=0—25) 的结构、磁性及输运性质.当Cr不断替代A位Co时,晶体结构逐渐从典型的L2₁结构过渡到Hg₂CuTi结构,晶格常数线性地增大0.69%.合金的磁性从Co_{2 关键词： CrCoGa Hesuler合金 KKR-CPA-LDA计算}     

Effect of Cr3+ ions on the magnetic moment of ferrites of the system CuFe2−x CrxO4

The dependence of the magnetic moment n _0exp of samples of the system CuFe_2−x Cr_xO₄ (x=0.0, 0.2, 0.3, 1.0, 1.4, 1.6, and 2.0) on their Cr³⁺ content is examined here for the first time. It is found that the experimental values of the magnetic moment n _0exp are much smaller than the values calculated from the cation distribution obtained previously (n _{0 theor}). It is suggested that this relationship (n _{0 theor}>n _{0 exp}) is due to a decrease in the magnetic moments of the Cr³⁺ ions resulting both from pairing of the t _2g orbitals of these cations in the octahedral sublattice and from a transfer of spin density from the ligands to the e _g orbitals of these ions. For compositions with x>1.0, the noncollinear magnetic structure also leads to an increase in the difference between n _{0 theor} and n _0exp. Fiz. Tverd. Tela (St. Petersburg) 40, 99–100 (January 1998)     

Y2(Fe1-x-y,Coy,Crx)17化合 物的结构及居里温度

通过x射线衍射及磁测量手段研究了Y₂(Fe_1-y-x,Co_y,C r_x)₁₇化合物的结 构及居里温度.研究结果表明Y₂(Fe_1-y-x,Co_y,Crx)₁₇化合物具有六 角相的Th₂Ni₁₇型结构.随着x的增加，Y₂(Fe 关键词： 2(Fe_1-y-x')" href="#">Y₂(Fe_1-y-x y')" href="#">Co_y x)_{1 7}化合物')" href="#">Cr_x)_{1 7}化合物 x射线衍射 居里温度     

Theoretical studies of structural, elastic, electronic and lattice dynamic properties of AlxYyB1−x−yN quaternary alloys

A theoretical study on the structural, elastic, electronic and lattice dynamic properties of Al_xY_yB_1−x−yN quaternary alloys in zinc-blend phase has been carried out with first-principles methods. Information on the lattice parameter, the lattice matching to available substrates and energy band-gaps is a prerequisite for many practical applications. The dependence of the lattice parameter a, bulk modulus B, elastic constants C₁₁, C₁₂ and C₄₄, band-gaps, optical phonon frequencies (ω_TO and ω_LO), the static and high-frequency dielectric coefficients ε (0) and ε (∞) and the dynamic effective charge Z^? were analyzed for y=0, 0.121, 0.241, 0.362 and 0.483. A significant deviation of the bulk modulus from linear concentration dependence was observed. A set of isotropic elastic parameters and related properties, namely bulk and shear moduli, Young's modulus, Poisson's ratio are numerically estimated in the frame work of the Voigt-Reuss-Hill approximation. The resistance to changes in bond length and lateral expansion in Al_xY_yB_1−x−yN increase with increasing y concentration. We observe that at y concentration about 0.035 and 0.063, Al_xY_yB_1−x−yN changes from brittle to ductile and Γ-X indirect fundamental gap becomes Γ-Γ direct fundamental gap. There is good agreement between our results and the available experimental data for the binary compound AlN, which is a support for those of the quaternary alloys that we report for the first time.     

First-principles calculations for the elastic properties of Ni-base model superalloys: Ni/Ni3Al multilayers

A model system consisting of Ni[001](100)/Ni3Al[001](100) multi-layers are studied using the density functional theory in order to explore the elastic properties of single crystal Ni-based superalloys. Simulation results are consistent with the experimental observation that rafted Ni-base superalloys virtually possess a cubic symmetry. The convergence of the elastic properties with respect to the thickness of the multilayers are tested by a series of multilayers from 2γ′+2γ to 10γ′+10γ atomic layers. The elastic properties are found to vary little with the increase of the multilayer’s thickness. A Ni/Ni3Al multilayer with 10γ′+10γ atomic layers (3.54 nm) can be used to simulate the mechanical properties of Ni-base model superalloys. Our calculated elastic constants, bulk modulus, orientation-dependent shear modulus and Young’s modulus, as well as the Zener anisotropy factor are all compatible with the measured results of Ni-base model superalloys R1 and the advanced commercial superalloys TMS-26, CMSX-4 at a low temperature. The mechanical properties as a function of the γ′ phase volume fraction are calculated by varying the proportion of the γ and γ′ phase in the multilayers. Besides, the mechanical properties of two-phase Ni/Ni3Al multilayer can be well predicted by the Voigt-Reuss-Hill rule of mixtures.     

Dependence of NiTi hydride stability by co-substitution by (Zr,Mg) onto Ti and (Cr,Cu) onto Ni: first-principles study

ABSTRACT

The thermodynamics of hydride formation is one of the most important properties of the metal-hydrogen system, and states its potential for further uptake. For this reason, much research is focused on the use of first principle calculations as a predictive tool in the study of hydride stability. In this paper, First-principles density functional calculations were performed to predict the effect of co-substitution in NiTiH, Ti by Mg and Zr (x?=?0.125, 0.25 and 0.375), as well as Ni by Cu and Cr (y?=?0.125). Structural, thermodynamic stability and electronic properties were investigated. The formation enthalpy when Ti is substituted either by Mg or Zr with respect to their content is calculated and compared to the host NiTiH; it is found that the hydride stability decreases as Mg content increases while it increases when Zr content increases. The substitution of Ni by Cu destabilises the hydride while the stability of the hydride is enhanced when Ni is substituted by Cr. The simultaneous substitution of Ti by Mg (x?=?0.375) and Ni by Cu (y?=?0.125), leads to considerable destabilisation and an increase in cell volume of the hydride. The corresponding Ni_0.875Cu_0.125Ti_0.625Mg_0.375 compound is identified with optimum characteristics among the considered compositions, thereby can be considered as potential material for hydrogen storage.     

Molecular orbital study of germanium,germanium-gallium and germanium-arsenic clusters

The quasirelativistic INDO/1 method has been used to generate molecular orbitals for some {Ge _x }, doped {Ge _x Ga _y } and {Ge _x As _y } clusters. These one-electron energy levels predefine the density of states (DOS) and/or hole functions. The effect of the cluster size (x=24, 56, 92) and that of dopants on the DOS profiles are discussed. The calculations are compared with those generated by periodic crystal orbitals of the EHT quality.     

Band structure and properties of superconducting MgB<Subscript>2</Subscript> and related compounds (A review)

This paper presents an overview of the current state of the art in research into the electronic structure and properties of a new superconductor, namely, MgB₂, and a large number of related compounds by computational methods of the band theory. Consideration is given to the specific features of the surface states of magnesium diboride, the electron and hole doping effects in this compound, and the concentration dependences of the band structure and the properties of Mg_1?xMe_xB₂ and MgB_2?yX_y solid solutions and a number of superstructures. The electronic properties of AlB₂-like phases, boron, higher borides, a series of ternary layered boron-containing phases, and compounds with structures of the antiperovskite type (MgCNi₃ and others) are discussed in terms of their superconducting characteristics. The results obtained in modeling nanotubes and fullerene-like nanoparticles based on MgB₂ and related borides are analyzed.     

Pr2Fe14(C,B)/α-(Fe,Co)型纳米晶复合磁体的结构与磁性

研究了Pr_xFe_82-x-yTi_yCo₁₀B₄C₄ (x=9—10.5;y=0, 2)纳米晶薄带的结构与磁性. 结果表明,所有薄带皆主要由2∶14∶1, 2∶17和α-(Fe, Co)三相组成. 对于y=0的合金,其内禀矫顽力随Pr含量x的增加而增加,剩磁随Pr含量x的增加而减小. 以Ti置换部分Fe (y=2),合金的磁性能得到显著提高,表现为:添加Ti后,合金的剩磁B_r基本不降低,x=10.5时合金的B_r值甚至有较明显的提高;同时添加Ti后,合金的内禀矫顽力及退磁曲线的方形度都明显改善. 当x=10.5,y=2时,合金薄带的磁性能达到最佳值为: B_r=9.6 kGs(1 Gs=10^-4 T),_iH_c =10.2 kOe(1 Oe=79.5775 A/m)和(BH)_max＝17.4 MGOe. 随着Pr含量的提高,合金中的硬磁相2 ∶14 ∶1的含量相对增加,内禀矫顽力提高;而Ti置换Fe抑制了软磁相α-(Fe, Co)在快淬和热处理过程中的优先长大,使合金中软磁相和硬磁相的晶粒尺寸及比例趋向最佳组合,交换耦合作用明显增强. 关键词： 纳米晶永磁材料 2Fe₁₄(C')" href="#">Pr₂Fe₁₄(C B) Ti添加 交换耦合     

Ferromagnetic nature of (Ga, Cr)As epilayers revealed by magnetic circular dichroism

A systematic study of magnetic circular dichroism (MCD) was carried out in a wave length range 500-960 nm for (Ga_1−x, Cr_x)As epilayers with x=2.38% and 4.59% grown by the low temperature molecular beam epitaxy (LT-MBE) technique. Hysteresis characteristics showed up indeed in the magnetic field dependence of both MCD and magnetization measured by the superconductor quantum interference device (SQUID). The Curie temperature of the (Ga_1−x, Cr_x)As epilayer was determined to be about 12 K by the Arrott approach. The present result provides evidences that there is strong coupling of the Cr spins to the GaAs host band structure in (Ga_1−x, Cr_x)As samples. That affects the critical point of the semiconductor host, and makes the magnetization behavior in a plot of M∼B/T (magnetic field divided by temperature) substantially different from standard superparamagnetism.     

Mechanical properties of bcc Fe-Cr alloys by first-principles simulations

The effect of chromium content on the fundamental mechanical properties of Fe-Cr alloys has been studied by first-principles calculations. Within a random solid solution model, the lattice constants and the elastic constants of ferromagnetic bcc Fe_1?x Cr _x (0? · ?0.156) alloys were calculated for different compositions. With addition of Cr content, the lattice parameters of Fe-Cr alloys are larger than that of pure Fe solid, and the corresponding Young??s modulus and shear modulus rise nonmonotonically with the increasing Cr content. All alloys (except 9.4 at% Cr) exhibit less ductile behavior compared with pure bcc Fe. For the Fe_1?x Cr _x (0? · ?0.156) alloys, the average magnetic moment per atom decreases linearly with the increasing Cr concentration.