(Nd1-xYx)3Fe27.31Ti1.69化合物的结构与磁性研究

制备了(Nd1-xYx)3Fe27.31Ti1.69(0≤x≤0.6)系列化合物,通过X射线衍射和磁性测量等手段研究了它们的结构和磁性.这些化合物均为Nd3(Fe,Ti)29型结构,A2/m空间群.化合物晶胞体积随Y含量增加而单调减少,居里温度Tc随Y含量增加略有降低,说明化合物的居里温度主要由Fe-Fe之间的交换相互作用所决定.温度为5K时,饱和磁化强度Ms随Y含量的增加而单调降低,与一个简单的稀释模型预期结果一致.所得化合物在低温下均发生自旋重取向,自旋重取向温度Tsr随Y含量增加而单调降低,从x=0时的232K减小到x=0.6时的121K.基于磁晶各向异性的研究结果确定了所得化合物的自旋相图.     

ErFe_(11)Ti化合物在流动氮气氛中的差热-热重分析

通过X射线衍射(XRD)、差热-热重(DTA-TG)联用仪以及磁测量等手段研究了ErFe11Ti化合物在流动氮气氛从室温(~300 K)到1473 K升温过程中成分、结构及居里温度等变化行为。结果表明,温度为600 K左右时,ErFe11Ti化合物吸氮反应最剧烈,吸氮以后化合物的居里温度TC有明显提高。当温度较高时,ErFe11Ti可能部分分解为Er-N,α-Fe(Ti)。α-Fe和Ti分别在860和1300 K左右发生吸氮反应,生成FeNy和Ti2N2。在整个升温过程中,DTA曲线未因样品升温至某成分的居里点发生而出现明显放热峰,这可能是因为样品的相变潜热较小所引起的。     

Tm2CrFe14.5Si1.5化合物的反常热膨胀性质研究

通过X射线衍射手段研究了Tm2CrFe14.5 Si1.5化合物的热膨胀性质及本征磁致伸缩性质.研究结果表明,Tm2CrFe14.5Si1.5化合物在303～623 K范围内,具有单相的Th2Ni17型结构;Tm2CrFe14.5Si1.5化合物的居里温度约为453 K,比其母合金Tm2 Fe17高约163 K;沿a轴方向上,Tm2CrFe 14.5 Si1.5化合物在423～448 K温度范围内出现负热膨胀现象,其热膨胀系数(α)a为-0.716×10-5/K;沿c轴方向上,在303～398 K温度范围内也出现负热膨胀现象,其热膨胀系数(α)c为-0.547×10-5/K.两者综合的结果使得在423～448 K温度范围内,Tm2CrFe14.5Si1.5化合物的体热膨胀系数(α)为-0.794 × 10-5/K.对本征磁致伸缩的研究结果表明,Tm2CrFe14.5 Si1.5化合物中存在着较强的各向异性的本征磁致伸缩.     

间隙原子氮对化合物RE2Fe17磁性的影响

用自旋极化的MS-Xα方法计算了稀土-过渡族化合物Nd2Fel7Nx(x=0,3)中含哑铃Fe原子对的Fe8及含Nd和N原子的NdFe6和NdFe6N3原子簇的电子结构和磁矩。计算结果显示，在化合物Nd2Fe17中，Fe(c)和Fe(f)晶位间的分子轨道中，有3个奇宇称轨道呈现负交换耦合。通过比较α-Fe的MX-Xα计算结果，能够很好地说明RE2Fel7化合物居里温度较低的原因。在化合物Nd2Fel7M中，Fe(c)-Fe(f)晶位间分子轨道只剩下一个奇宇称轨道呈现弱的负交换耦合，通过比较N2Fe17和Nd2Fe17N3化合物Fe8原子簇的计算结果，能够很好地说明间隙原子M对化合物RE2Fel7Mx(M表示N，H或C)的居里温度产生影响的物理机制。对RE2Fel7型化合物中影响Fe-Fe交换耦合的主要因素，本文也做了讨论。     

Nd_(1-y)Dy_yFe_(11-x)TiM_x(M=Mo,Si)系列化合物中Mo,Si元素的掺杂对其结构及磁性能的影响

通过电弧方法制备了一系列的Nd1-yDyyFe11-xTiMx(M=Mo,Si)型稀土过渡金属化合物,并且通过X射线衍射和中子衍射对其晶体结构进行了研究.实验发现,Nd1-yDyyFe11-xTiMx(M=Mo,Si)系列中化合物主要结构为ThMn12-type(1︰12相).Dy取代Nd没有明显影响1︰12相形成的含量.在Nd0.5Dy0.5Fe11-xTiMx(M=Mo,Si)系列中,当x≤0.8时Nd0.5Dy0.5Fe11-xTiMox化合物主要呈ThMn12-type晶形,当x0.8时,化合物中1︰12相的含量降至80%以下;对于Nd0.5Dy0.5Fe11-xTiSix,当x≤0.6时,Nd0.5Dy0.5Fe11-xTiSix化合物主要呈ThMn12-type晶形,当x0.6时,化合物中1︰12相的含量降至90%以下但保持在80%以上.在不同的化合物中,稳定元素的含量不同.ThMn12-type相的百分含量随着Mo和Si取代Fe含量的增加而减小,意味着Mo和Si取代更多的Fe时,ThMn12-type相将变得不稳定.Nd0.5Dy0.5Fe11-xTiMox化合物的晶格参数a和c以及晶胞体积V随着Mo(x)含量的增加呈线性增加是因为Mo的原子半径比其中的Fe的大;而Nd0.5Dy0.5Fe11-xTiSix合金的晶格参数a和c以及晶胞体积V随着Si(x)含量的增加呈线性减小是因为Si的原子半径比其中的Fe的小.在NdyDy1-yFe11-xTiMx(M=Mo,Si)中,因为Ti和Mo的半径比Fe大而Si的半径比Fe小,所以Ti和Mo原子优先占据8i晶位,Si原子优先占据8j和8f晶位.在化合物RFe12-xMx中,居里温度由T-T交换作用决定的,由于T-T交换作用依赖于T-T原子距离,因此其他元素对Fe的取代导致了居里温度的改变.磁性测量表明Mo或Si取代Fe均导致居里温度的降低.     

钒,铬对快速凝固Al-Ti-Fe合金的组织结构与显微硬度的影响

利用X射线衍射(XRD)和透射电镜(TEM)研究了V, CrAl-Ti-Fe合金组织及显微硬度的影响. 结果表明 Al-Ti-Fe-(V,Cr)合金急冷态组织均为过饱和Al基固溶体; 300 ℃×10 h处理后, Al-2.5Ti-2.5Fe-2.5Cr合金析出Al3Ti和Al13Cr2相; 400 ℃×10 h处理后, Al-Ti-Fe-(V,Cr)合金均析出Al13Fe4相.随退火温度的升高, 快速凝固Al-2.5Ti-2.5Fe-2.5V合金的显微硬度略有下降, 快速凝固Al-2.5Ti-2.5Fe-2.5Cr合金的显微硬度略有上升,表明V, Cr元素的加入有利于快凝Al-2.5Ti-2.5Fe合金显微硬度的增加.     

不同工艺和原料对Mn_(1.2)Fe_(0.8)P_(0.48)Si_(0.52)化合物磁热效应的影响

用不同的工艺和原料制备了3个名义成分相同的Mn1.2Fe0.8P0.48S i0.52化合物。X射线衍射结果表明,3个化合物均为Fe2P型六角结构(空间群为P-62m),并且存在少量的(Fe,Mn)3S i相。通过磁性测量发现,3个样品的居里温度有所不同,但是都在室温附近(270~290 K)。以Fe2P为原料制备的化合物具有较大的磁熵变,在1.5 T的磁场变化下其最大磁熵变为13.6 J.(kg.K)-1。以行星样品球磨机制备的化合物具有较小的热滞,最小热滞为6.7 K。这些表明不同的制备工艺和原料对化合物的居里温度、热滞和磁熵变都具有一定的影响。同时低成本的原料、简单的制备工艺、较小的热滞和较大的磁熵变使得Mn1.2Fe0.8P0.48S i0.52化合物成为一种理想的室温磁致冷候选材料。     

硼对硬磁性Nd60Fe20Al10Co10大块非晶合金的磁性与晶化行为的影响

利用示差扫描量热法，X射线衍射法和振动样品磁强计研究了少量B元素对Nd60Fe20All0Col0大块非晶合金的磁性和晶化行为的影响。研究表明，用B元素部分取代Nd元素后，其内禀矫顽力有所增大，饱和磁化强度降低。晶化后，Nd60Fe20All0Col0大块非晶合金退火折出的晶体相对硬磁性能无明显影响，而Nd58Fe20All0Col0B2合金退火析出非铁磁性的Nd1.lFe4B4相，使内禀矫顽力、饱和磁化强度、居里温度降低。     

铈对00Cr17铁素体不锈钢高温抗氧化性的影响

利用电子分析天平、场发射扫描电镜、XRD衍射仪研究了不同Ce含量对00Cr17铁素体不锈钢高温抗氧化性的影响。结果表明:00Cr17钢中加入Ce后,钢的抗氧化性能得到提高,在1000℃以上时效果更加显著。氧化温度在700~1000℃范围内,随着Ce添加量的增加,氧化速率常数kp减小,氧化激活能提高,氧化膜由Cr2O3单相组成,而氧化温度在1100℃时,实验钢的氧化膜由Cr2O3和Fe2O3两相组成,Ce减缓了Fe2O3相的形成速率。Ce改善00Cr17铁素体不锈钢抗氧性的主要原因是降低了氧化物的生长速率,提高了氧化膜的致密性,增强了氧化膜与基体的粘附性。     

稀土过渡金属CaCu5型衍生化合物结构的原子级模拟

稀土过渡族金属化合物是功能材料研究领域的重要对象. 本文综述了CaCu5衍生型稀土过渡金属化合物Rn-mM5n 2m结构和变换关系的传统内容、含义, 以及在应用中的有效性和局限性. 从原子间相互作用势出发, 通过能量最小化对5类二元本征结构SmFe5, Sm2Fe17(H), Sm2Fe17(R), SmFe12(t), Sm3Fe29的空间群及晶格参数进行了计算, 并由此确定了这5类结构间的变换矩阵, 与传统矩阵变换关系作了对照, 分析了它们相近和相异的原因. 讨论了第三元素Cr, Ti对Sm3Fe29结构的稳定作用, 以及对晶体几何参数及X光谱的影响, 这都是传统矩阵变换反映不了的.     

KCl-KBO2-K2CO3, K2MoO4-KBO2-K2CO3, and K2WO4-KBO2-K2CO3 ternary systems

phase diagrams of KCl-KBO₂-K₂CO₃, K₂MoO₄-KBO₂-K₂CO₃, and K₂WO₄-KBO₂-K₂CO₃ ternary systems were studied by a calculation-experimental method and differential thermal analysis (DTA). The coordinates of ternary eutectics were determined to be E ₁: 622°C, 8.5 mol % KBO₂, 56.5 mol % KCl, and 35 mol % K₂CO₃; E ₂: 710°C, 23 mol % KBO₂, 43 mol % K₂CO₃, and 34 mol % K₂MoO₄; E ₃: 710°C, 23 mol % KBO₂, 43 mol % K₂CO₃, and 34 mol % K₂WO₄. The specific heats of melting of the eutectics were determined.     

Phase relations in the K2W2O7-K2WO4-KPO3-Bi2O3 system and structure of K6.5Bi2.5W4P6O34

The phase relations in the cross-section of the K₂W₂O₇-K₂WO₄-KPO₃ containing 15 mol% Bi₂O₃ were undertaken using flux method. Crystallization fields of K_6.5Bi_2.5W₄P₆O₃₄, K₂Bi(PO₄)(WO₄), Bi₂WO₆, KBi(WO₄)₂ and their cocrystallization areas were identified. Novel phase K_6.5Bi_2.5W₄P₆O₃₄ was characterized by single-crystal X-ray diffraction: sp. gr. P−1, a=9.4170(5), b=9.7166(4), c=17.6050(7) Å, α=90.052(5)°, β=103.880(5)° and γ=90.125(5)°. It has a layered structure, which contains {K₇Bi₅W₈P₁₂O₆₈}_∞ layers stacked parallel to ab plane and sheets composed by potassium atoms separating these layers. Sandwich-like {K₇Bi₅W₈P₁₂O₆₈}_∞ layers are assembled from [W₂P₂O₁₃]_∞ and [BiPO₄]_∞ building units, and are penetrated by tunnels with K/Bi atoms inside. FTIR-spectra of K₂Bi(PO₄)(WO₄) and K_6.5Bi_2.5W₄P₆O₃₄ were discussed on the basis of factor group theory.     

Sol-gel synthesis of K3InF6 and structural characterization of K2InC10O10H6F9, K3InC12O14H4F18 and K3InC12O12F18

K₃InF₆ is synthesized by a sol-gel route starting from indium and potassium acetates dissolved in isopropanol in the stoichiometry 1:3, with trifluoroacetic acid as fluorinating agent. The crystal structures of the organic precursors were solved by X-ray diffraction methods on single crystals. Three organic compounds were isolated and identified: K₂InC₁₀O₁₀H₆F₉, K₃InC₁₂O₁₄H₄F₁₈ and K₃InC₁₂O₁₂F₁₈. The first one, deficient in potassium in comparison with the initial stoichiometry, is unstable. In its crystal structure, acetate as well as trifluoroacetate anions are coordinated to the indium atom. The two other precursors are obtained, respectively, by quick and slow evaporation of the solution. They correspond to the final organic compounds, which give K₃InF₆ by decomposition at high temperature. The crystal structure of K₃InC₁₂O₁₄H₄F₁₈ is characterized by complex anions [In(CF₃COO)₄(OH_x)₂]^(5−2x)− and isolated [CF₃COOH_2−x]^(x−1)− molecules with x=2 or 1, surrounded by K⁺ cations. The crystal structure of K₃InC₁₂O₁₂F₁₈ is only constituted by complex anions [In(CF₃COO)₆]³⁻ and K⁺ cations. For all these compounds, potassium cations ensure only the electroneutrality of the structure. IR spectra of K₂InC₁₀O₁₀H₆F₉ and K₃InC₁₂O₁₂F₁₈ were also performed at room temperature on pulverized crystals.     

Solubility in the Na2Cr2O7-(NH4)2Cr2O7-K2Cr2O7-H2O system

Solubility in the Na₂Cr₂O₇-(NH₄)₂Cr₂O₇-K₂Cr₂O₇-H₂O four-component water-salt system at 25, 50, and 75°C was studied for the first time. Phase field boundaries for individual salts and potassium and ammonium dichromate solid solutions, monovariant lines, and invariant points were determined. Experimental data were used to optimize the looped isohydric process of potassium dichromate preparation involving additional salts.     

NaBO2-NaCl-Na2CO3, NaBO2- Na2CO3-NaMoO4, NaBO2- Na2CO3-NaWO4, and NaBO2-NaCl-Na2WO4 ternary systems

The phase diagrams of the NaBO₂-NaCl-Na₂CO₃, NaBO₂-Na₂CO₃-Na₂MoO₄, NaBO₂- Na₂CO₃-Na₂WO₄, and NaBO₂-NaCl-Na₂WO₄ ternary systems were studied by a calculation-experimental method and differential thermal analysis. The coordinates of ternary eutectics were determined: E ₁: 612°C, 16 mol % NaBO₂, 42 mol % NaCl, and 42 mol % Na₂CO₃; E ₂: 568°C, 12 mol % NaBO₂, 28 mol % Na₂CO₃, and 60 mol % Na₂MoO₄; E ₃: 575°C, 12 mol % NaBO₂, 32 mol % Na₂CO₃, and 56 mol % Na₂WO₄; E ₄: 628°C, 8 mol % NaBO₂, 20 mol % NaCl, and 72 mol % Na₂WO₄; and E ₅: 655°C, 9 mol % NaBO₂, 53 mol % NaCl, and 38 mol % Na₂WO₄.     

Li2SO4-Na2SO4-H2O和Li2SO4- K2SO4-H2O溶液的体积性质

本文用高精度数字式振荡管密度计测定了288K至318K温度范围内Li₂SO₄ + Na₂SO₄ + H₂O和 Li₂SO₄ + K₂SO₄ + H₂O三元体系的密度。混合溶液的离子强度范围从0.1到4.5 mol.kg_–1,混合溶液中Na₂SO₄和K₂SO₄的离子强度分数为0.2,0.4,0.6和0.8。用密度实验值拟合得到了不同温度下Pitzer离子相互作用模型混合参数θ_V和 ψ_V,模型的计算值与实验值的偏差在±0.002 g.cm_–3以内。用Pitzer模型计算了不同离子强度下三元体系的混合体积。     

Extension of the La7Mo7O30 structural type with La7Nb3W4O30 and La7Ta3W4O30 compounds

Two compounds of formula La₇A₃W₄O₃₀ (with A=Nb and Ta) were prepared by solid-state reaction at 1450 and 1490 °C. They crystallize in the rhombohedric space group R-3 (No. 148), with the hexagonal parameters: , and , . The structure of the materials was analyzed from X-ray, neutron and electronic diffraction. These oxides are isostructural of the reduced molybdenum compound La₇Mo₇O₃₀, which are formed of perovskite rod along [111]. An order between (Nb, Ta) and W is observed.     

SnSbBiS4-SnS and SnSbBiS4-Sn2Sb6S11 sections of the SnS-Sb2S3-Bi2S3 ternary system

SnSbBiS₄-SnS and SnSbBiS₄-Sn₂Sb₆S₁₁ sections were studied by physicochemical methods (DTA, X-ray powder diffraction, microstructure observation, and microhardness measurements). These sections were found to be eutectic quasi-binary sections of the SnS-Sb₂S₃-Bi₂S₃ ternary system. Solid solution regions based on the initial components were found on either side of the sections. Alloys in the solid solution region are p-type semiconductors.     

Theoretical study of polyoxide clusters B20O30, Al20O30, V20O50, Si20O30H20, and Si20O30F20

The structural, electronic, and vibrational characteristics and energies of the isolated polyoxide clusters B₂₀O₃₀, Al₂₀O₃₀, V₂₀O₅₀, Si₂₀O₃₀H₂₀, and Si₂₀O₃₀F₂₀ and their complexes with the H⁻ ion and ammonia complexes Al₂₀O₃₀ · nNH₃ have been calculated by the density functional theory B3LYP method with different basis sets. The computation results show that the symmetric closo structure I _h with oxygen bridges located above the centers of the faces of an empty [M₂₀] dodecahedron is more favorable for V₂₀O₅₀, Si₂₀O₃₀H₂₀, and Si₂₀O₃₀F₂₀. For B₂₀O₃₀, the cage closo isomer is also more favorable than the other isomers, but its structure is severely distorted as compared to a dodecahedron and has a symmetry close to C ₃ . For Al₂₀O₃₀, the I _h structure corresponds to a high-lying local minimum of the potential energy surface. For Al₂₀O₃₀, a set of unusual puckshaped isomers of symmetry C _i , with different numbers of four-coordinate atoms ^IVAl and three-coordinate atoms ^IIIO, was localized; these structures are more than 90 kcal/mol more favorable than the dodecahedron I _h . The most favorable isomer of Al₂₀O₃₀ contains twelve four-coordinate atoms ^IVAl and four five-coordinate atoms ^VAl. The energies of dissociation of the most favorable M₂₀O₃₀ clusters into the M₂O₃ (C _2v ) and M₄O₆ (T _d ) fragments and, in the case of Al₂₀O₃₀, also into the Al₈O₁₂ (O _h ) and Al₁₂O₁₈ (D _3d ) fragments, have been estimated. The conclusion has been drawn that these clusters can, in principle, exist and can be experimentally detected in the isolated state. Analogous calculations have been performed for ammonia complexes Al₂₀O₃₀ · nNH₃ with n varying from 1 to 20. The effect of solvation on the relative stability of the dodecahedral and puckshaped isomers of the Al₂₀O₃₀ cluster is observed. The isomers with ammonia molecules in their first coordination sphere become much closer to one another on the energy scale; however, the dodecahedron remains a considerably less favorable intermediate. Original Russian Text ? O.P. Charkin, N.M. Klimenko, D.O. Charkin, 2008, published in Zhurnal Neorganicheskoi Khimii, 2008, Vol. 53, No. 4, pp. 624–635.     

Structural chemistry of Sr3Cr2WO9, Ca3Cr2WO9, and Ba3Cr2WO9

We have studied the preparation and crystallographic structure of three perovskite-type compounds: Sr₃Cr₂WO₉, cubic, the lattice parameter of which is a = 7.812Å; Ca₃Cr₂WO₉, tetragonal, the lattice parameters of which are a = 5.408 Å and c = 7.635Å; and Ba₃Cr₂WO₉, hexagonal, the lattice parameters of which are a = 5.691 Å and c = 13.957Å. We have compared these three structures and shown the relationship between the dimensions of the alkaline-earth metal and the existence of the different structures.