The effect of Fe on the martensitic transformation of TaRu high-temperature shape memory alloys:A first-principles study

The effect of Fe on the martensitic transformation of TaRu high-temperature shape memory alloys has been investigated using first-principles calculations. The site preference of Fe in TaRu alloys has been clarified for the first time, and the results show that Fe is predicted to occupy Ru sites. The addition of Fe increases the stability of the Ta₅₀Ru_50-xFe_x β phase, leading to a significant decrease in the β to β′ martensitic transformation temperature. In addition, the mechanism of the Fe alloying effect is explained on the basis of the electronic structure.     

用于电压基准的Nb/NbxSi1-x/Nb约瑟夫森单结的研制

现代可编程约瑟夫森电压基准的核心器件是约瑟夫森结阵.目前最具有优势的约瑟夫森结阵是 Nb/Nb_xSi_1-x/Nb材料的结阵. Nb/Nb_xSi_1-x/Nb材料的约瑟夫森结 具有三层薄膜的制作过程简便, Nb和Nb_xSi_1-x刻蚀工艺相同以及Nb_xSi_1-x 势垒层成分可调等优点.中国计量科学研究院设计制作了Nb/Nb_xSi_1-x/Nb约瑟夫森单结. 通过在4.2 K低温下对所做单结进行直流电流-电压特性测量,观测到了清晰的超导隧穿电流和 从零电压态向电压态的跳变,最后就测量结果进行了分析讨论.此项工作属于国内首个开展 Nb/Nb_xSi_1-x/Nb材料约瑟夫森单结研究的工作.     

The effect of Si content on the martensitic transfor-mation temperature of Ni55.5e18Ga26.5-xSix alloys

This paper investigates the effects of substitution of Si for Ga on the martensitic transformation behaviours in Ni-Fe-Ga alloys by using optical metallographic microscope and differential scanning calorimetry (DSC) methods. The structure type of Ni_55.5Fe₁₈Ga_26.5-xSi_x alloys is determined by x-ray diffraction (XRD), and the XRD patterns show the microstructure of Ni-Fe-Ga-Si alloys transformed from body-centred tetragonal martensite (with Si content x = 0) to body-centred cubic austenite (with x = 2) at room temperature. The martensitic transformation temperatures of the Ni_55.5Fe₁₈Ga_26.5-xSi_x alloys decrease almost linearly with increasing Si content in the Si content range of x ≤ 3. Thermal treatment also plays an important role on martensitic transformation temperatures in the Ni-Fe-Ga-Si alloy. The valence electronic concentrations, size factor, L2₁ degree of order and strength of parent phase influence the martensitic transformation temperatures of the Ni-Fe-Ga-Si alloys. An understanding of the relationship between martensitic transformation temperatures and Si content will be significant for designing an appropriate Ni-Fe-Ga-Si alloy for a specific application at a given temperature.     

Effects of added elements and strain on the martensitic phase transformation of Nb3Sn

X-ray studies show the effects of elements added to the Nb or of strain on the martensitic phase transformation of Nb₃Sn at low temperature. Additives to the Nb suppress the transformation, superimposed strains produced by a surrounding bronze matrix tend to mask the lattice transformation, and calculations show that the detailed line shape must be considered.     

Effect of Nb<Superscript>5+</Superscript> charge neutralization substitution on the electrochemical performance of lithium-rich layered oxides

The effect of the Nb⁵⁺ substitution with a charge-compensated strategy in lithium-rich layered oxides (LLOs) Li_1.2Ni_0.13+xCo_0.13-xMn_0.54-xNb_xO₂ (x?=?0, 0.01, 0.02, and 0.03) has been investigated systematically. A hydroxide co-precipitation method followed by a high-temperature solid-state reaction is adopted in the synthesis process. Structural characterization confirms that the low dose substituting of Nb⁵⁺ in the layered structures forms a solid solution, and the samples show low cation mixing and enlarged Li⁺-diffusing channels, which imply favorable high-rate capability. The initial charge/discharge measurements suggest that the oxygen loss from the network during the delithiation process has been suppressed by the substitution of Nb⁵⁺ due to the formation of robust Nb–O bonds and a decrease in TM-O (TMs are transition metals) covalence. Moreover, these Nb–O bonds contribute to the stabilization of the crystalline framework, resulting in an excellent cycle stability with a mitigated voltage decay.     

哈斯勒合金Ni-Mn-Ga的马氏体相变和磁增强双向形状记忆效应

通过研究铁磁性金属间化合物Ni_2+xMn_1-xGa(x=-0.1,0,0.08,0.13,0.18,0.2)和Ni_2-xMn_1+x/2Ga_1+x/2(x=-0.1,0,0.04,0.06,0.1)两个系列多晶样品的交流磁化率随温度的变化行为,得到了化合物在不同组分下的马氏体相变温度TM和居里温度T_C.发现随着Ni成分的增加,前者的马氏体相变温度T_m增加,而居里温度T_C降低,后者的马氏体相变温度T_m和居里温度T_C均是先增大后减小.报道了T_m在室温附近的单晶样品Ni₅₂Mn₂₄Ga₂₄的磁场增强双向形状记忆效应.发现伴随着马氏体相变,样品在[001]方向可产生1.2%的收缩.如果在该方向施加1.2T的偏磁场可以使该应变值增大到4.0%.而垂直于[001]方向施加1.2T的偏磁场时,在[001]方向产生1.6%的膨胀.阐明了产生大应变的原因并非相界移动,而是单晶的杂散内应力小和外加磁场通过孪晶界移动使马氏体变体重组的共同结果. 关键词： 形状记忆效应 马氏体相变 2MnGa')" href="#">Ni₂MnGa     

BiFe1-xNbxO3的结构、磁性和光学性质

用溶胶凝胶法制备了Nb掺杂多铁BiFe_1-xNb_xO₃粉晶样品（0 <x <0.05）,研究Nb掺杂对样品的结构、磁学和光学性质的影响。根据XRD图谱和Rietveld精修的结果可知,所有的样品仍保持R3c相,但晶格常数a,c,晶胞体积V和Fe-O-Fe键角发生变化。适当的Nb掺杂使得样品晶粒尺寸减小,导致剩余磁化强度的增强,使得BiFe_1-xNb_xO₃样品的禁带窄化.     

The effect of Nb addition on the thermal stability and magnetic properties of Fe-based amorphous alloys with a wide supercooled liquid region

We have examined the effect of Nb addition on the thermal stability of the supercooled liquid before crystallization, the glass-forming ability and magnetic properties for the amorphous alloy series Fe₇₃Nb_xAl_5-xGe₂P₁₀C₆B₄ and Fe₆₃Co₇Nb_xZr_10-xB₂₀. The supercooled liquid regions (ΔT_x=T_x-T_g) have maximum values of 66 and 79K, respectively, for Fe₇₃Nb₁Al₄Ge₂P₁₀C₆B₄ and Fe₆₃Co₇Nb₄Zr₆B₂₀ alloys. The saturation magnetization σ_s of the Fe₇₃Nb_xAl_5-xGe₂P₁₀C₆B₄ alloy system is much higher than that of the Fe₆₃Co₇Nb_xZr_10-xB₂₀ alloy system, and is almost unchanged with an increasing Nb content from 0 to 3 at%. But the σ_s of the Fe₆₃Co₇Nb_xZr_10-xB₂₀ alloys decreases linearly with increasing Nb content. The coercive force H_c of the two alloy series can have a minimum value of 31A/m for Fe₇₃Nb₁Al₄Ge₂P₁₀C₆B₄ and 37A/m for Fe₆₃Co₇Nb₄Zr₆B₂₀. All these values are for the ribbons annealed at 773 and 873K for 15min in vacuum.     

Nb对C-15结构V2(HfZr)系列的超导转变温度的影响

本文中研究了C-15结构V₂Hf_1-xNb_x,V₂Zr_1-xNb_x和V₂Hf_0.5Zr_0.5-xNb_x系列的超导转变温度T_c与Nb合量x的关系,发现V₂Zr,V₂Hf加Nb后与V₂Hf_0.5Zr_0.5加Nb后性能显著不同。测定了V₂Zr,V₂Hf和V₂Hf_0.5Zr_0.5的X射线光电子能谱。结果表明,当Hf原子和Zr原子共存于AB₂化合物的A位上时,发生了一种增强原子间相互作用的新的电荷转移。这个事实支持由角动量分波表象能带论方法分析电声耦合超导原理的结果对四元V₂(HfZrNb)系列的超导行为提出的一种可能解释:4d-5d原子配位可能有助于提高4d导带的杂化程度,从而有利于提高超导T_c。 关键词：     

四元Heusler合金NiMnFeGa中Fe原子的磁性贡献

用熔炼和甩带的方法制备了组分为Ni₅₀Fe_xMn_25-xGa ₂₅(x=0—25) 的系列样品.x射线衍射实验结果表明，当Fe取代Mn的含量x＜17时，用熔炼和甩带的方法均 能合成高度有序的L2₁结构的Heusler相.而当x＞17时，普通熔炼方法只能得到 低有序度的 γ相，只有采用甩带急冷的方法才能获得高度有序的纯L2₁结构的化合物.根据 交流磁化率 和分子磁矩的测试结果，初步分析了Fe原子对化合物磁性的贡献，认为Fe原子占据了Mn原子 的位置后，具有高于一般含铁合金的原子磁矩，可达2.55—3.55μ_B. 关键词： Heusler合金 50Fe_xMn_25-xGa_{25')" href="#">Ni50FexMn25-xGa25}     

Martensitic transformation in Cu-doped NiMnGa magnetic shape memory alloys

This paper studies the martensitic transformation in the Cu-doped NiMnGa alloys. The orthorhombic martensite transforms to L2₁ cubic austenite by Cu substituting for Ni in the Ni_50-xCu_xMn₃₁Ga₁₉ (x=2--10) alloys, the martensitic transformation temperature decreases significantly with the rate of 40 K per Cu atom addition. The variation of the Fermi sphere radius (k_F) is applied to evaluate the change of the martensitic transformation temperature. The increase of k_F leads to the increase of the martensitic transformation temperature.     

Effect of Co on magnetic property and phase stability of Ni--Mn--Ga ferromagnetic shape memory alloys: A first-principles study

The effect of Co content on magnetic property and phase stability of Ni50-xMn25Ga25Cox ferromagnetic shape memory alloys has been investigated using first-principles calculations. The total energy difference between paramagnetic and ferromagnetic state of austenite plays an important role in the magnetic transition. The high Curie temperature can be attributed to the stronger Co-Mn exchange interaction as compared to the Ni-Mn one. The phase stability of Ni50-xMn25Ga25Cox austenite increases with increasing Co content, which is discussed based on the electronic structure.     

Magnetic interaction in Mg, Ti, Nb doped manganites

An effect of Mn substitution with Me=Mg²⁺, Ti⁴⁺, Nb⁵⁺ in manganites has been investigated by preparing La_0.7Sr_0.3(Mn_1-xMe_x)O₃ and La_1-xSr_x(Mn_{1 - x/2}Nb_x/2)O₃ series. It was established that substitution of manganese with magnesium up to x = 0.16 leads to a collapse of a long-range ferromagnetic order whereas La_0.7Sr_0.3(Mn ^{3 +} _0.85Nb ^{5 +} _0.15)O₃ is ferromagnet with T _C = 123 K and exhibits a large magnetoresistance below Curie point despite an absence of four-valent manganese. Hypothetical magnetic phase diagrams are constructed for La_0.7Sr_0.3(Mn_1-xMe_x)O₃ and La_1-xSr_x(Mn_{1 - x/2}Nb_x/2)O₃. Our results show that Mn³⁺-O-Mn³⁺ exchange interaction is ferromagnetic in the orbitally disordered manganites as well as an increase of Mn⁴⁺ content above 50% from a total amount of manganese ions leads to formation of a spin glass state due to a competition between antiferromagnetic Mn⁴⁺-O-Mn⁴⁺ and ferromagnetic Mn³⁺-O-Mn⁴⁺(Mn³⁺) superexchange interactions. Received 24 January 2002 Published online 9 July 2002     

Nd-Fe(Co,Nb)-B交换耦合磁体的磁性

用熔体快淬法结合热处理制备了高性能纳米复合永磁合金Nd₉Fe_85.5-xCo_xNb₁B_4.5(0≤x≤16).最佳磁性能对应的成分为Nd₉Fe_81.5Nb₁B_4.5,其永磁性能如下：最大磁能积(BH)_max＝156kJ/m³,剩磁J_r＝1.11T 关键词：     

High-temperature thermoelectric characteristics of B-site substituted Yb0.1Ca0.9Mn1−x Nb x O3 system (0≤x≤0.1)

The thermoelectric performance of Yb_0.1Ca_0.9MnO₃ doped with Nb⁵⁺ at B-site is investigated in this paper. It is found that there is a phase transition from O-type to O*-type orthorhombic structure with increasing of Nb doping content, which indicates that the structure distortion becomes more seriously. Since the electron–phonon interaction can be enhanced by the structure distortion, the small polaron formation is promoted in Yb_0.1Ca_0.9Mn_1?x Nb _x O₃ with increasing Nb content. In the whole measured temperature range, the electrical conductivity can be fitted very well by the adiabatic small polaron hopping model. The activated energy E _α is ascending with increasing Nb content. The temperature dependence of Seebeck coefficient S of Yb_0.1Ca_0.9Mn_1?x Nb _x O₃ shows that the S is basically inversive to the charge carrier concentration. S(T) can be fitted well by the Cutler and Mott model, which indicates that the density of state around the Fermi level is strongly affected by Nb-doping at B-site. It is contrary to those of CaMnO₃ and RE_0.1Ca_0.9MnO₃, when Nb content x>0.05, the |S| and σ show a same tendency of the temperature dependence.     

Influence of the martensitic structure transformation in LaAg x In1−x on the magnetic properties of substituted Ce

The martensitic phase transformation has no observable effect on the magnetic susceptibility of Ce in LaAg _x In_1–x which agrees with the assumption of a crystal field splitting by 300 K of the² F _5/2 ground state of Ce³⁺ ions. The magnetic ordering temperature and the Kondo minimum move to higher temperatures together with the martensitic phase transformation when the Ag concentration is reduced. This behavior can be related qualitatively to the lowering of the 5d – e _g levels in the center of the Brillouin-zone with increasing In content.     

Influence of the martensitic structure transformation in LaAgxIn1?x on the magnetic properties of substituted Ce

The martensitic phase transformation has no observable effect on the magnetic susceptibility of Ce in LaAg _x In_1–x which agrees with the assumption of a crystal field splitting by 300 K of the² F _5/2 ground state of Ce³⁺ ions. The magnetic ordering temperature and the Kondo minimum move to higher temperatures together with the martensitic phase transformation when the Ag concentration is reduced. This behavior can be related qualitatively to the lowering of the 5d – e _g levels in the center of the Brillouin-zone with increasing In content.     

Superconducting and magnetic properties of Nb/Pd 1-xFex/Nb triple layers

The superconducting and magnetic properties of Nb/Pd_1-xFe_x/Nb triple layers with constant Nb layer thickness d_Nb=200 ? and different interlayer thicknesses 3 ?≤ d_PdFe ≤ ? are investigated. The thickness dependence of the magnetization and of the superconducting transition temperature shows that for small iron concentration x the Pd_1-xFe_x layer is likely to be in the paramagnetic state for very thin films whereas ferromagnetic order is established for x ≥ 0.13. The parallel critical field B_c2||(T){B_{c2||}}(T) exhibits a transition from two-dimensional (2D) behavior where the Nb films are coupled across the interlayer, towards a 2D behavior of decoupled Nb films with increasing d_PdFeand/or x. This transition allows a determination of the penetration depth x_F{\xi _F} of Cooper pairs into the Pd_1-xFe_x layer as a function of x. For samples with a ferromagnetic interlayer x_F{\xi _F} is found to be independent of x.     

Temperature dependence of phase separation and magnetic anisotropy by electron spin resonance in Pr<Subscript>0.6</Subscript> Ca<Subscript>0.4</Subscript> Mn<Subscript>0.9</Subscript> Ru<Subscript>0.1</Subscript>O<Subscript>3</Subscript>

Electron spin resonance (ESR) measurements have been performed on polycrystalline samples of Pr_0.6Ca_0.4Mn_1-xRu_xO₃ (x = 0, 0.1). The substitution of Ru in the Mn-site strengthens ferromagnetic interactions due to the double exchange between the Mn³⁺ and Mn⁴⁺ species and super-exchange between the Ru⁵⁺ and Mn³⁺ species. The temperature dependence of the ESR spectra indicates development of magnetic phase separation in Pr_0.6Ca_0.4Mn_0.9Ru_0.1O₃ in contrast with the un-doped sample.     

Effect of Mn incorporation for Ni on the properties of melt spun off-stoichiometric compositions of NiMnGa alloys

The investigation addresses the effect of Mn incorporation for Ni on the properties of a series of Ni_77−xMn_xGa₂₃ (x=22-29; at%) ferromagnetic shape memory alloys prepared in the form of ribbons by a melt spinning technique. Phase transformation studies in these ribbons by differential scanning calorimetry revealed that austenitic start and martensitic start temperatures decreased with the increase in Mn content. The Curie temperature (T_C) of these alloys determined from thermal variation of magnetisations was found to rise with increasing Mn content. The martensitic transformation temperatures were above T_C in low Mn containing (x=22 and 23) alloys. Morphology observed through transmission electron microscopy manifested complex martensitic features in the alloy with x=22 while x=29 had an austenitic phase. The alloys with intermediate Mn content (x=24, 25) had overlapping magnetic and martensitic transformations close to room temperature. The thermal lag between austenitic and martensitic characteristic temperatures in these alloys has been corroborated to their structural state. X-ray diffraction indicated a predominant martensite phase and austenite phase in low and high Mn containing alloys respectively. In-situ diffraction studies during thermal cycle indicate martensite-austenite transformations.