Influence of Ni/Mn ratio on magnetostructural transformation and magnetocaloric effect in Ni_(48-x)Co_2Mn_(38+x)Sn_(12)(x = 0, 1.0, 1.5, 2.0,and 2.5) ferromagnetic shape memory alloys

An investigation on the magnetostructural transformation and magnetocaloric properties of Ni_(48-x)Co_2Mn_(38+x)Sn_(12)(x = 0, 1.0, 1.5, 2.0, and 2.5) ferromagnetic shape memory alloys is carried out. With the partial replacement of Ni by Mn in the Ni_(48)Co_2Mn_(38)Sn_(12) alloy, the electron concentration decreases. As a result, the martensitic transformation temperature is decreased into the temperature window between the Curie-temperatures of austenite and martensite. Thus, the samples with x = 1.5 and 2.0 exhibit the magnetostructural transformation between the weak-magnetization martensite and ferromagnetic austenite at room temperature. The structural transformation can be induced not only by the temperature,but also by the magnetic field. Accompanied by the magnetic-field-induced magnetostructural transformation, a considerable magnetocaloric effect is observed. With the increase of x, the maximum entropy change decreases, but the effective magnetic cooling capacity increases.     

Sm3（F3,Co,Mn）29 compounds：promising materials for permanent magnets

The outstanding hard-magnetic properties are reported of Sm_3Fe_{28.1-x}Co_xMo_{0.9} compounds with x=12, 14, 16. In this alloy system, only a small amount of Mo is needed to stabilize the 3:29 structure so that the magnetic properties are not seriously affected by the presence of this nonmagnetic element. Substitution of Co for Fe leads to a significant increase of the magnetic anisotropy, and for x≥14 the easy magnetization direction changes from easy plane to the easy axis. In this alloy system, the compound Sm_3Fe_{12.1}Co_{16}Mo_{0.9} is a very promising candidate for permanent magnet applications. Its room temperature saturation magnetization (μ_0M_s=1.5 T) and anisotropy field (B_{an}=6.5 T) are comparable to the values for Nd_2Fe_{14}B (μ_0M_s=1.6 T and B_{an}=7 T). However, the Curie temperature of Sm_3Fe_{12.1}Co_{16}Mo_{0.9} is 1020 K, which is appreciably higher than that for Nd_2Fe_{14}B (T_C=588 K).     

Heredity of clusters in the rapidly cooling processes of Al-doped Zr_(50)Cu_(50) melts and its correlation with the glass-forming ability

The heredity of clusters in rapidly cooled(Zr_(50)Cu_(50))_(100-x)Al_x melts and its correlation with glass-forming ability(GFA) are studied via molecular dynamics simulations. Pair distribution function and the largest standard cluster(LSC)are adopted to characterize the local atomic structures in the(Zr_(50)Cu_(50))_(100-x)Al_x systems. The [12/555] icosahedra and their medium-range order(IMRO) play an important role in forming(Zr_(50)Cu_(50))_(100-x)Al_x metallic glasses(MGs). The fraction of [12/555], the number of IMRO, and the maximum size of IMRO in MGs increase significantly with increasing x. A tracking study further reveals that the configuration heredity of icosahedral clusters starts from supercooled liquids.No direct correlation exists between the GFA and the onset temperature of continuous or stated heredity. Instead, a larger hereditary supercooled degree of icosahedra matches with better GFA of Al-doped Zr_(50)Cu_(50) alloys.     

Y0.5Gd0.5Ba2Cu3O7-δ体系中通氧时间对超导转变温度的影响

研究了高温氧化物超导体Y0.5Gd0.5Ba2Cu3O7-δ体系中通氧时间对超导转变温度及超导转变温区的影响。Y0.5Gd0.5Ba2Cu3O7-δ样品是按相等摩尔数的Gd与Y元素配比,采用传统的固相反应法烧结而成的多晶块材。实验结果显示:Y0.5Gd0.5Ba2Cu3O7-δ烧结样品与YBa2Cu3O7-δ烧结样品均具有很好的单相性,在一定的通氧条件下其超导临界转变温度TC与超导初始转变温度TCO值相对YBa2Cu3O7-δ烧结样品有提高。文中对此结果进行了讨论。     

Co-P非晶态合金电子性质和局域结构的理论研究

根据Co P非晶态合金结构的短程有序和结构中可能存在P -P相互作用的实验事实 ,选择了单磷原子簇模型ConP(n =1～ 5 )和双磷原子簇模型ConP2 (n =1～ 4 ) ,用密度泛函理论方法对其进行计算 .结果表明 ,在单磷Co2 P( 2 ) 、Co3 P( 1) 及Co4P( 2 ) 模型体系中 ,Co原子供给P原子电子 ,与电负性规则一致 ,同时Co和P之间具较强化学作用 ,可以形成稳定的原子簇 ;而在双磷和单磷原子簇Co5P( 1) 模型体系中 ,形成的原子簇不稳定 ,采用单磷Co2 P( 2 ) 、Co3 P( 1) 及Co4P( 2 ) 模型能较好地反映Co P非晶态合金的结构特点 .     

Evidence for strain glass in the ferroelastic-martensitic system Ti(50-x)Ni(50+x)

We report here "strain glass," a new glassy phenomenon in ferroelastic-martensitic system of Ni-rich intermetallic Ti(50-x)Ni(50+x) (x > 1), where local strain is frozen in disordered configuration below a critical temperature Tg. The ac elastic modulus shows a minimum at Tg, which exhibits logarithmic frequency dependence following Vogel-Fulcher relationship, and the corresponding internal friction shows a frequency-dependent peak located at a lower temperature. In situ high-resolution transmission electron microscopy observations reveal uncorrelated nanoclusters of martensiticlike phase, randomly frozen in the otherwise untransformed parentlike matrix. Being parallel to spin glass and relaxor, strain glass may shed new light on the fundamental physics of glass and lead to the discovery of novel properties.     

Cu50Ni50合金快速凝固的分子动力学模拟

采用分子动力学模拟的方法研究了Cu₅₀Ni₅₀合金在不同冷却速度下的凝固过程,利用均方位移、径向分布函数和结构可视化等方法分析其微观结构.并对凝固模型进行拉伸模拟,通过应力应变曲线和直观结构变化分析其性能.研究表明：冷却速度对Cu₅₀Ni₅₀合金凝固形成的结构有较大影响,随着冷却速度的升高,凝固形成的结构中晶体含量减少,在较低的冷却速度下,如冷却1×10¹²K/s时,Cu₅₀Ni₅₀合金凝固形成晶体结构;在较高的冷却速度下,如1×10¹⁴K/s时,Cu₅₀Ni₅₀合金凝固形成非晶体结构,且非晶Cu₅₀Ni₅₀合金的抗拉性能要优于晶体Cu₅₀Ni₅₀合金.     

Electrochemical corrosion and oxidation resistances of Zr_(60)Ni_(21)Al_(19) bulk amorphous alloys

Electrochemical corrosion and oxidation resistances of Zr 60 Ni 21 Al 19 amorphous alloy were studied. The ternary amorphous alloy exhibits greater positive potential than its crystalline counterpart and 0Cr19Ni9Ti stainless steel. Its weight loss result measured in 2 mol/L HCl solution is in agreement with the potentiodynamic curve. But there is no obvious difference in the oxidation resistances between Zr 60 Ni 21 Al 19 amorphous and its crystalline alloys. They both exhibit high oxidation resistance.     

Effect of Sb-doping on martensitic transformation and magnetocaloric effect in Mn-rich Mn_(50)Ni_(40)Sn_(10-x)Sb_x(x=1,2,3,and 4) alloys

We investigate the influence of Sb-doping on the martensitic transformation and magnetocaloric effect in Mn_(50)Ni_(40)Sn_(10-x)Sb_x(x = 1, 2, 3, and 4) alloys. All the prepared samples exhibit a B2-type structure with the space group F m3 m at room temperature. The substitution of Sb increases the valence electron concentration and decreases the unit cell volume. As a result, the magnetostructural transformation shifts rapidly towards higher temperatures as x increases.The changes in magnetic entropy under different magnetic field variations are explored around this transformation. The isothermal magnetization curves exhibit typical metamagnetic behavior, indicating that the magnetostructural transformation can be induced by a magnetic field. The tunable martensitic transformation and magnetic entropy changes suggest that Mn_(50)Ni_(40)Sn_(10-x)Sb_x alloys are attractive candidates for applications in solid-state refrigeration.     

Molecular dynamics simulations of supercooled and amorphous Co(100-x)Zr(x): atomic mobilities and structural properties

Molecular dynamics simulations are reported on Co(100-x)Zrx in the complete range of compositions. The simulations are based on Hausleitner-Hafner potentials. For the glassy states of the alloys, a comparison of simulated pair-correlation functions with experimental data is presented. Diffusivities were evaluated for the liquid and supercooled melt from isothermal simulation runs. Therefrom a strong dependency on alloy composition is found for the critical temperature T(c)(x) of the mode-coupling theory. Lines of constant averaged diffusivity in the supercooled melts scale closely with this temperature. The ratio of the component diffusivities shows a more involved variation with temperature and composition. These variations reflect differences in the amorphous structure of the alloys, which are quantified in terms of the chemical short-range-order at the level of tetrahedral clusters.     

Quadrupole splitting on57Fe nuclei and local structure of the amorphous alloys Ni−Zr,Ni−Ta

Quadrupole splittings on⁵⁷Fe nuclei were studied by Mössbauer spectroscopy in amorphous and crystalline Ni-based alloys with 37 at .% Zr and 25–50 at .% Ta with 0.5 at .%⁵⁷Fe addition. Quadrupole splitting distributions and then the topological short range in Ni?Ta alloys were found to be similar to that of the Ni₃Ta intermetallic compound. The distribution of splittigs for Ni?Zr alloy is similar to that of its crystalline counterpart.     

非晶La_(1-x)Nd_xP_5O_(14)的拉曼散射研究

本文利用拉曼散射对非晶 La_(1-X)Nd_XP_5O_(14)及其晶化过程进行了研究。拉曼散射表明在非晶La_(1-X)Nd_XP_5O_(14)中仍保留着晶态 La_(1-X)Nd_XP_5O_(14)中具有的 PO_4~(3-)四面体结构单元。非晶La_(1-X)Nd_XP_5O_4在不同温度下晶化,其拉曼谱线的频率不同,这一现象可用应力模型给予解释。     

哈斯勒合金Ni-Co-Mn-Sn的马氏体相变及其磁热效应研究

通过结构和磁性测量,研究了四元哈斯勒合金Ni_50-xCo_xMn₃₈Sn₁₂（x=1, 2, 4, 6, 8）的晶体结构和相变特征.结果表明,Co原子的掺杂不但没有影响三元哈斯勒合金Ni-Mn-Sn的原有结构,而且还增强了样品在奥氏体相的铁磁交换作用.此外,通过Maxwell方程计算了其中三种成分样品（x= 2, 4, 6）的磁熵变ΔS_{M关键词： 哈斯勒合金 Ni-Co-Mn-Sn 马氏体相变 磁热效应}     

非晶态合金Cu_xPd_(1-x)形成过程合金效应及微观结构转变特性的模拟研究(英文)

本文根据量子Sutton-Chen多体势,采用分子动力学方法对含有50000个原子大系统液态二元合金Cu_xPd_(1-x)(CuPd的原子半径比为1.14)在快速凝固过程中的微观结构转变特性进行模拟研究.运用Honeycutt-Andersen(HA)键型指数法和原子成团类型指数法(CTIM)分析了液态和固态的微观结构特性.研究结果发现:在7.73×10~(13)K/S冷却速率下,Cu_xPd_(1-x)合金形成以1551、1541和1431三种键型为主的非晶态结构;系统以1551键型和由1551键型构成的(12 0 12 0)二十面体团族在所有的键型和团簇中占主导地位,并且在液态合金Cu_xPd_(1-x)微观结构转变中起着关键性作用.通过分析键型、团簇和平均原子体积,我们发现液态合金Cu_xPd_(1-x)的玻璃转变温度是573K.同时还发现,原子的平均配位数的变化与1551,1441,1661键型的变化趋势相当接近,这反映出体系对称性结构的变化规律与配位数的变化有关.     

Estimation of surface tension for high temperature melts of the binary Ag-X alloys

ABSTRACT

Surface tension is a key property to materials. In this work, the surface tension of the binary alloys Ag-X (Au, Cu, Ce, Bi, Sn, Sb, In, Ni, Y, Pd) is carried out by using Butler Model over enter composition ratio at a certain temperature. According to calculation results, the increasing surface tension of the Ag-X (Cu, Au, Ni, Y, Pd) alloy is accompanied by the composition increases. For Ag-Sn alloy, the surface tension calculated by Butler model is consistent with the experimental result at temperature 1273?K. However, other Ag-X alloys can’t be compared due to the lack of the related experimental data. Although the experimental data about surface tension of the Ag-X alloy are limited, we are possible to make a comparison between the calculated results for the surface tension in this study and the available experimental data. Taken together, the surface tension calculated by Butler model that especially the Ag-Sn alloy are consistent with the experimental results at temperature 1273?K.     

Phase equilibrium of Cd_(1-x)Zn_xS alloys studied by first-principles calculations and Monte Carlo simulations

The first-principles calculations based on density functional theory combined with cluster expansion techniques and Monte Carlo(MC) simulations were used to study the phase diagrams of both wurtzite(WZ) and zinc-blende(ZB)Cd_(1-x)Zn_xS alloys.All formation energies are positive for WZ and ZB Cd_(1-x)Zn_xS alloys,which means that the Cd_(1-x)Zn_xS alloys are unstable and have a tendency to phase separation.For WZ and ZB Cd_(1-x)Zn_xS alloys,the consolute temperatures are 655 K and 604 K,respectively,and they both have an asymmetric miscibility gap.We obtained the spatial distributions of Cd and Zn atoms in WZ and ZB Cd_(0.5)Zn_(0.5)S alloys at different temperatures by MC simulations.We found that both WZ and ZB phases of Cd_(0.5)Zn_(0.5)S alloy exhibit phase segregation of Cd and Zn atoms at low temperature,which is consistent with the phase diagrams.     

STM/AFM studies of the evolution of morphology of electroplated Ni/W alloys

The surface morphology evolution of Ni/W alloys was studied, as a function of the alloy composition. Using the modified plating baths developed in our laboratory recently, electroplated Ni/W alloys with different W content, in the range of 7–67 atom percent (a/o), can be obtained. This was found to lead to different structures, ranging from polycrystalline fcc-Ni type structure to amorphous, followed by orthorhombic with increasing W content in the alloy. Powder XRD was studied to determine the crystal structures. Ex situ STM, AFM and SEM were used to study in detail the surface morphologies of the different alloys, and their evolution with increasing W content.

The important findings are that a mixture of two crystalline forms can give rise to an amorphous structure. Hillocks that are usually a characteristic of epitaxial growth can also exist in the amorphous alloys. Oriented scratches caused by stress can also be formed.

Up to 20 a/o of W is deposited in the alloys in crystalline form, with the fcc-Ni type structure. Between 20 and about 40 a/o an amorphous structure is observed, and above that an orthorhombic crystal structure is seen, which is characteristic of the NiW binary alloy. Careful choice of the composition of the plating bath allowed us to deposit an alloy containing 67 a/o W, which corresponds to the composition NiW₂.     

Fe掺杂La0．8Sr0．2Co1-xFexO3磁性的研究

利用溶胶-凝胶法制备了一系列的La0.8Sr0.2Co1-xFexO3样品.通过研究在不同外加磁场下磁化强度和温度变化的关系发现,在较高的外场下La0.8Sr0.2Co1-xFexO3样品的磁性反转现象没有被观察到;在低场下La0.8Sr0.2Co1-xFexO3系统磁性反转现象被实现.这说明Fe的掺杂引起了La0.8Sr0.2Co1-xFexO3样品中铁磁和反铁磁之间的竞争,导致了La0.8Sr0.2Co1-xFexO3样品磁性反转;同时外加磁场的强弱影响了La0.8Sr0.2Co1-xFexO3系统磁性反转现象的发生,外加磁场增大使得在La0.8Sr0.2Co1-xFexO3样品中Co离子的自旋平行趋势更强,在铁磁和反铁磁之间的竞争中铁磁耦合占主导优势,因此在较高的外场下磁性反转现象没有被观察到.     

Effects of Cu on the martensitic transformation and magnetic properties of Mn_(50)Ni_(40)In_(10) alloy

The structures, the martensitic transformations, and the magnetic properties are studied systematically in Mn50Ni40-xCuxIn10, Mn50-xCuxNi40In10, and Mn50Ni40In10-xCux alloys. The partial substitution of Ni by Cu reduces the martensitic transformation temperature, but has little influence on the Curie temperature of austenite. Comparatively, the martensitic transformation temperature increases and the Curie temperature of austenite decreases with the partial replacement of Mn or In by Cu. The magnetization difference between the austenite phase and the martensite phase reaches 70 emu/g in Mn50Ni39Cu1In10; a field-induced martensite-to-austenite transition is observed in this alloy.     

A study of thermal parameters of Ag50Pd50 alloy using X-ray diffraction

Thermal parameters of Ag₅₀Pd₅₀ alloy were studied using the in-situ X-ray diffraction (XRD) technique. Diffraction experiments in the temperature range 308-1178 K showed that the alloy forms a face centered cubic (fcc; A1-type) structure. Temperature dependence of the lattice parameter was investigated using the Bragg line displacement method. Results show that the lattice parameter for the alloy increases with increase in temperature. The temperature dependent XRD data was utilized to determine the mean linear thermal expansion (MLTE (%)) and coefficient of thermal expansion (CTE) ‘α’ in the mentioned temperature range. It was observed that the values of CTE vary between 9.3 and 14.6 [K⁻¹][10⁻⁶]. The same data was also utilized to determine the Debye temperatures Θ_D and mean square amplitude of vibration (MSAV) (u²(T)) for this alloy. Values of thermal parameters as determined in this investigation are in good agreement with the estimated values as well as with those for other alloys of noble metals.