Structure of Y3TaNi6+xAl26: a filled-up substitution variant of the BaHg11 type

The crystal structure of Y₃TaNi_6+xAl₂₆ (refined composition Y₄TaNi_6+[7]Al_20+[6]) was determined by single-crystal X-ray diffraction (λ(Mo K) −0.71073 A. μ −17.827 mm¹, F(000) = 700, T = 293 K, wR = 0.015 for [8] unique reflections). This new quaternary aluminide crystallizes with a cubic structure. Pearson code cP49-12.85, (221) Pm-3m-ji'gdba, a = 8.3600(1) Å. V = 584.28(2) Å, Z = 1, M₁ = 1510.25, D_x = 4.292 mg mm¹. The structure of Y_xTaNi_6+xAl₂₆ is filled-up substitution variant of the BaHg₁₁ structure type with one additional atom site, partly occupied (around 15%) by Ni atoms, located at the centre of a cube formed by Al atoms. Distinct atom coordinates were refined for Ni and Al atoms on a site for which mixed occupation (approximately 50% Ni/50% Al) was found. The Ta atoms centre regular Al atom cuboctahedra, and the Y atoms 20-vertex polyhedra, formed by Al and Ni atoms, similar to those observed in CeMn₄Al₈ and YbFe₂Al₁₀.     

Synthese und kristallstruktur von KCr0,8Al0,2Mo2O8

Single crystals of KCr_0.8Al_0.2Mo₂O₈ were prepared and investigated by the X-ray diffractometer technique. It shows a structure type related to trigonal KAIMo₂O₈, monoclinic NaCrMo₂O₈ or orthorhombic KInMo₂O₈, space group C_2h⁶—C2/c; a=17.445 Å, b=5.649 Å, c=8.997 Å, β=119.37°; Z=4. KCr_0.8Al_0.2Mo₂O₈ is characterized by isolated MoO₄ tetrahedra, isolated (Cr/Al)O₆ octahedra and a distorted square antiprism around K⁺. The crystal structure is discussed with respect to those of related compounds.

Zusammenfassung

Einkristalle von KCr_0.8Al_0.2Mo₂O₈ wurden synthetisiert und mit Vierkreisdiffraktometertechnik röntgenographisch untersucht. Sie zeigen einen mit trigonal-KA1Mo₂O₈, monoklin-NaCrMo₂O₈ oder orthorhombisch-KlnMo₂O₈ verwandten Strukturtyp, Raumgruppe C_2h⁶—C2/c; a=17,445 Å, b=5,649 Å, c=8,997 Å, β=119,37°; Z=4. KCr_0.8Al_0.2Mo₂O₈ zeichnet sich durch isolierte MoO₄-Tetraeder, isolierte (Cr/Al)O₆-Oktaeder und ein verzerrtes quadratisches Antiprisma um K⁺ aus. Die Kristallstruktur wird mit solchen verwandter Verbindungen diskutiert.     

Structure of the ternary phase Co3Al8Ga and formation of the gallium-containing decagonal phase d-Co(Al, Ga)3(m)

The structure of the ternary phase Co₃Al₈Ga, Pearson symbol oI96, space group Immm, a=12.0081(7) Å, b=7.5701(6) Å, c=15.394(1) Å is isotypic with Co₂NiAl₉. Powder diffraction data are reported for this ternary intermetallic compound. Using liquid quenching, the metastable pseudoternary decagonal phase d-Co(Al, Ga)₃(m) was obtained in the aluminium-rich portion of the ternary system Co–Al–Ga. Gallium substitutes for aluminium atoms in the d-Co(Al, Ga)₃(m) phase up to a mol fraction x_Ga=0.10. In the phase of the binary system Co–Al richest in aluminium, Co₂Al₉, the aluminium atomic positions can be occupied by gallium up to a gallium content of x_Ga=0.05.     

Nanocrystalline LaNi4−xMn0.75Al0.25Cox electrode materials prepared by mechanical alloying (0≤x≤1.0)

Polycrystalline hydrogen storage alloys based on lanthanum (La) are commercially used as negative electrode materials for the nickel–metal hydride (Ni–MH_x) batteries. In this paper, mechanical alloying (MA) was used to synthesize nanocrystalline LaNi_4−xMn_0.75Al_0.25Co_x (x=0, 0.25, 0.5, 0.75 and 1.0) hydrogen storage materials. XRD analysis showed that, after 30 h milling, the starting mixture of the elements decomposed into an amorphous phase. Following the annealing in high purity argon at 700 °C for 0.5 h, XRD confirmed the formation of the CaCu₅-type structures with a crystallite sizes of about 25 nm. The nanocrystalline materials were used as negative electrodes for a Ni–MH_x battery. Cobalt substituting nickel in LaNi₄Mn_0.75Al_0.25 greatly improved the discharge capacity and cycle life of the LaNi₅ material. For example, in the nanocrystalline LaNi_3.75Mn_0.75Al_0.25Co_0.25 powder, discharge capacities up to 258 mA h g⁻¹ (at 40 mA g⁻¹ discharge current) were measured. Mechanical alloying is a suitable procedure to obtain LaNi₅-type alloy powders for electrochemical energy storage.     

X-ray investigations of ternary R3Pd4Ge4 samples

Ternary R₃Pd₄Ge₄ samples (R=Nd, Eu, Er) were investigated by means of X-ray single crystal (four circle diffractometer Philips PW1100, MoK radiation) and powder diffraction (MX Labo diffractometer, CuK radiation). The Er₃Pd_3.68(1)Ge₄ compound belongs to the Gd₃Cu₄Ge₄ structure type, space group Immm, a=4.220(2) Å, b=6.843(2) Å, c=14.078(3) Å, R₁=0.0484 for 598 reflections with F_o>4σ(F_o) from X-ray single crystal diffraction data. No ternary R₃Pd₄Ge₄ compound when R is Nd or Eu was observed. The Nd and Eu containing samples appeared to be multiphase. Ternary phases observed in the Nd₃Pd₄Ge₄ and Eu₃Pd₄Ge₄ alloys and their crystallographic characteristics are the following: NdPd₂Ge₂, CeGa₂Al₂ structure type, space group I4/mmm, a=4.3010(2) Å, c=10.0633(2) Å (X-ray powder diffraction data); NdPd_0.6Ge_1.4, AlB₂ structure type, space group P6/mmm, a=4.2305(2) Å, c=4.1723(2) Å (X-ray powder diffraction data); Nd(Pd_0.464(1)Ge_0.536(1))₂, KHg₂ structure type, space group Imma, a=4.469(2) Å, b=7.214(2) Å, c=7.651(3) Å, R₁=0.0402 for 189 reflections with F_o>4σ(F_o) (X-ray single crystal diffraction data); Eu(Pd,Ge)₂, AlB₂ structure type, space group P6/mmm, a=4.311(2) Å, c=4.235(2) Å; EuPdGe, EuNiGe structure type, space group P2₁/c, and ternary compound with unknown structure (X-ray powder diffraction data).     

Determination of the structure of UFe2Al10 compound

The atomic structure of a new ternary phase UFe₂Al₁₀ appearing in the U–Fe–Al system was determined using direct methods applied to X-ray powder diffraction data. High resolution electron microscopy combined with the methods of crystallographic image processing was used for the verification of the structural model. The UFe₂Al₁₀ phase is orthorhombic and belongs to Cmcm space group, its unit cell contains 40 Al, eight Fe, and four U atoms. The lattice parameters obtained after Rietveld refinement are: a=8.919 Å, b=10.208 Å, and c=9.018 Å. The reliability factors characterizing the Rietveld refinement procedure are: R_p=5.9%, R_wp=8.1%, and R_b=2.9%.     

The crystal structure and magnetic properties of the Gd6Cr4Al43 compound

The crystal structure of intermetallic compound Gd₆Cr₄Al₄₃ has been investigated by means of X-ray diffraction data (Ho₆Mo₄Al₄₃ structure type, space group P6₃/mcm, Pearson symbol hP106, a = 10.9144(7) Å, c = 17.7361(13) Å).

SQUID magnetic measurements carried out for the title compound point to the existence of two antiferromagnetic phase transitions observed at T_N1 = 19.0(1) K and T_N2 = 6.8(1) K, respectively.     

Al25Nb20Ti30Zr25低密度高熵合金的组织和性能

通过Thermo-Calc软件计算、微观组织多尺度表征以及热模拟试验等研究了Al₂₅Nb₂₀Ti₃₀Zr₂₅合金的组织结构、高温组织稳定性和热加工性能。结果表明,Al₂₅Nb₂₀Ti₃₀Zr₂₅合金的铸锭组织主要由BCC基体相和Zr₅Al₃析出相组成,Zr₅Al₃相在BCC晶界连续析出,晶粒内部的Zr₅Al₃相呈块状分布,平均尺寸在750 nm左右;合金在750~1000 ℃保温24 h后,基体中的晶粒尺寸并未发生明显变化;随着温度的增加,Zr₅Al₃相含量小幅度降低,合金的高温组织稳定性较好。建立了合金的本构方程为$\dot{ε}$=4.5×10¹⁴×[sinh(0.0063σ_p)]^2.8exp(-419/RT),并绘制了合金的能量耗散系数图;在1050 ℃/1 s^-1变形条件下,能量耗散系数达到峰值0.69,在该变形条件下等温锻造出尺寸为$\phi$ 180 mm×20 mm完整无开裂的圆形块体材料。锻造消除了原始晶界处连续分布的Zr₅Al₃相,使其分解成短杆状均匀分布于合金基体中,BCC基体组织发生了动态回复和部分再结晶。     

Electronic structure and thermoelectric power of CeNi4Si

The studies of the thermoelectric power and band structure calculations for CeNi₄Si are reported. These studied are supported by magnetic susceptibility, electrical resistivity, specific heat and X-ray photoemission spectroscopy measurements. CeNi₄Si is paramagnetic down to 2 K and follows the Curie–Weiss law with μ_eff = 0.52μ_B/f.u. and the paramagnetic Curie temperature θ_P = −2 K. This effective paramagnetic moment is lower than the free Ce³⁺ value. The obtained values for the f occupancy n_f and for the coupling Δ of the f level with the conduction states are in good agreement with the values found for mixed valence compounds. Below the Fermi energy the total density of states contains mainly the d states of Ni atoms. The narrow peaks of the f states of Ce atoms were found above the Fermi level. CeNi₄Si is characterized by γ = 16 mJ mol⁻¹ K⁻² and θ_D = 335 K.     

On the peritectoid formation of Ni5Al3

The peritectoid formation of Ni₅Al₃ from the two phases NiAl and Ni₃Al was studied in a Ni---Al alloy containing 66 at% Ni by means of transmission electron microscopy. The product phase does not form as a uniform layer between the two initial phases as expected and already observed in a few systems. In the system studied here there are only very few nucleation sites located at the NiAl/Ni₃Al interface. The further growth of Ni₅Al₃ takes place only into one of the initial phases which is NiAl. A strict orientation relationship between NiAl and Ni₅Al₃ was observed; the growth direction was [221]. The transformation is presumably diffusion controlled; it is very sluggish and it can be described by a nucleation and growth process. From the study presented here we conclude that the formation of Ni₅Al₃ proceeds by a micromechanism which differs from that normally assumed for peritectoid reactions.     

Hydrogen storage properties of melt-spun LaNi4.25Al0.75

Rapidly solidified LaNi_4.25Al_0.75 alloy was prepared by melt spinning and its hydrogen storage properties were examined. The hydrogen storage capacities and the equilibrium pressures of the unannealed melt-spun (UMS) LaNi_4.25Al_0.75 alloy were found to be nearly identical to those of the annealed induction-melt (AIM) alloy. However, the resistance to pulverization was greatly improved and the hysteresis was markedly decreased for the UMS alloy, while its activation became rather difficult.     

ESR bottleneck effect in dilute Gd1−xLaxT2Si2 (T=Cu, Ni) systems

The bottleneck effect observed in electron spin resonance (ESR) was removed by replacing the Gd^3. spins by non-magnetic lanthanum ions in two compounds: the most bottlenecked GdCu₂Si₂ and GdNi₂Si₂ where the bottleneck is weaker. The unbottlenecked limit was reached for very small Gd concentrations to (1 −x) = 0.0005. From these results the ν(E_F)J_Sc values have been estimated, where ν(E_F) is the electron density of states at the Fermi level and J_Sc is the exchange coupling constant between conduction electrons and Gd spins. It was found that these values are twice as large for Ni compounds (15 × 10³) as for Cu compounds (7.5 × 10³). On the basis of X-ray photoemission spectra of the valence band and theoretical calculations of ν(E_F) for LaCu₂Si₂, the density of states is estimated as 0.15 states per eV spin atom for GdCu₂Si₂ and 0.3 states per eV spin atom for GdNi₂Si₂ (for J_Sc = 0.05 eV). The relaxation processes in the investigated compounds are also discussed.     

The influence of titanium on the electrochemical properties of the AB5-type metal hydrides

AB₅-type intermetallic compounds were prepared by arc-melting in argon atmosphere. The composition of a stoichiometric compound LaNi_3.6Al_0.4Co_0.7Mn_0.3 with a hexagonal CaCu₅ structure was varied by stoichiometric and nonstoichiometric addition of Ti. With the increase of the Ti y0.05 content in LaNi_3.6Al_0.4Co_0.7Mn_0.3Ti_y, the hydrogen storage capacity is enhanced, whereas when y=0.1–0.3, it is decreased. The discharge capacity and cyclability are increased considerably by addition of titanium in the range of 0.02–0.1 with a maximum value at about 0.1%. The highest maximum capacity is achieved for a nonstoichiometric addition of 0.05% Ti. The kinetic properties are also additionally improved by the formation of a titanium-rich second phase. This can explain the improvement of the capacity for alloys with low Ti content. The decrease in capacity for high Ti content was also correlated with the amount of the Ti-rich phase. Therefore, the improvement of kinetics are due to the catalytic effect, grain boundary diffusion effect or more pronounced alloy pulverization upon cycling. This study has been aimed to improve the electrode properties of a series of multicomponent LaNi_3.6Al_0.4Co_0.7Mn_0.3Ti_y (y=0.0, 0.02, 0.05, 0.1, 0.2, 0.3) alloys which have mutual complementary properties. All the prepared alloys have been subjected to analyses by EDS, SEM and XRD. In order to determine the hydrogen storage capacity, the pressure composition isotherms (P–C–T curves) have been used. The metal hydride electrodes were characterized by galvanostatic cycling test.     

Ni-CeO2复合镀层厚度对δ-Ni2Al3-CeO2/Ni-CeO2涂层体系扩散行为的影响

在Ni基体电沉积不同厚度的Ni-CeO₂复合镀层并对其进行620 °C低温渗铝,制备了剩余复合镀层厚度分别约为10和45 μm厚的δ-Ni₂Al₃-CeO₂/Ni-CeO₂涂层体系。1000 °C真空退火5 h后,以上两种涂层体系均可在铝化物/镀层界面形成CeO₂富集层。但剩余复合镀层厚度为10 μm的涂层体系由于氧化物富集程度不足,涂层退化程度较剩余复合镀层厚度为45 μm的涂层体系严重。可见,在镀层氧化物颗粒含量一定的情况下,渗铝后剩余镀层厚度是影响扩散障有效性的重要因素。     

BaO对CaO-Al2O3基保护渣熔化温度、结晶及微观结构的影响

CaO-Al₂O₃基保护渣在解决高铝钢连铸过程渣-金反应性问题中展现了巨大潜力,但仍存在结晶能力过强、熔化温度偏高等问题。因此,研究了BaO对CaO-Al₂O₃-CaF₂-B₂O₃-Na₂O-Li₂O-MgO多元渣系熔化温度、结晶行为和微观结构的影响。研究结果表明,BaO的加入降低了渣系软化温度和熔化温度,随着BaO含量的增加,降低程度减弱;BaO的加入使渣系结晶相由Ca₁₂Al₁₄O₃₃和Ca₃B₂O₆ 2相共同析出转变为Ca₁₂Al₁₄O₃₃、Ca₃B₂O₆和BaAl₂O₄ 3相共同析出,且随着BaO 的增加,渣系结晶温度降低,结晶能力减弱;Ba2+对[AlO₄]5-具有较强电价补偿效应,使其能够稳定存在,Al-O网络结合更为紧密,游离O2-难以进入孔隙中破坏桥氧链接,从而导致网络聚合度轻微升高,原子扩散能力降低,提高了结晶动力学势垒,抑制了结晶。     

The ytterbium-copper-aluminium system

The isothermal section of the Yb---Cu---Al phase diagram at 870 K over the whole concentration region has been constructed using X-ray structure and phase analysis. We have confirmed the existence of earlier reported ternary compounds: YbCuAl (ZrNiAl type) and YbCu₄Al₈ (CeMn₄Al₈ type); the previously reported compound YbCu₄Al proved to be a solid solution of aluminium in the binary compound YbCu₅ (CaCu₅). New ternary aluminides such as Yb₄(Cu_0.26Al_0.74)₃₃ (new structure type), Yb₂(Cu_0.57Al_0.43)₁₇ (Th₂Zn₁₇), Yb(Cu_0.85Al_0.15)₆ (YbMo₂Al₄)₇ Yb₆(Cu_0.74Al_0.26)₂₃ (Th₆Mh₂₃) and Yb(Cu_0.30Al_0.70)₃ (PuNi₃) have been prepared for the first time and their crystal structures have been determined. The limits of solid solutions of the binary compound YbCu₅ and the homogeneity ranges of the ternary phases Yb(CuAl)₁₂, Yb(CuAl)₁₇ and Yb(CuAl)₂ have been established.     

The molybdenum diphosphate Mo1.3O(P2O7), containing Mo2 and Mo3 clusters

A novel molybdenum diphosphate, Mo_1.3O(P₂O₇), was obtained by electrochemical lithium deintercalation. The diphosphate crystallises in space group I2/a with the lattice parameters a=22.88(1), b=22.94(2), c=4.832(1) Å, γ=90.36°, Z=8. Its original framework is built up from MoO₆ octahedra, P₂O₇ groups and also from MoO₄, Mo₂O₄ and Mo₃O₈ units containing Mo₂ and Mo₃ clusters. These polyhedra delimit large octagonal and z-shaped tunnels running along c, in which the inserted cations may be located.     

Existence, structure and valence properties of the skutterudites CeyFe4−xCoxSb12

We report on sample preparation, annealing effects, electron microprobe analysis in the series Ce_yFe_4−xCo_xSb₁₂ which shows that a phase separation occurs for substituted samples (0<x<4) annealed at 650 and 550 °C. Single phase samples are obtained for either Ce_yFe₄Sb₁₂ or Ce_yCo₄Sb₁₂ samples annealed at 650 °C and for all compositions when annealed at 700 °C. The valence state of Ce in homogeneous samples has been studied using X-ray absorption spectroscopy (XAS). Ce ions are trivalent throughout the series and the XAS spectra does not show effect of the crystal field on the 5d-final state.     

Magnetocrystalline anisotropy of R2Fe17Hx (x=0, 3) single crystals

The magnetocrystalline anisotropy of R₂Fe₁₇ (R=Y, Gd, Tb, Ho and Er) and their hydrides are studied by analyzing the magnetization curves of single crystal samples in the temperature range 4.2–300 K in magnetic fields up to 140 kOe. There is no noticeable influence of hydrogenation on the magnetic anisotropy in the Y₂Fe₁₇ and Gd₂Fe₁₇ compounds. An easy-plane to easy-cone transition is detected for a Tb₂Fe₁₇H₃ single crystal after hydrogenation. A significant change of the magnetization process has been observed in the hydrides Ho₂Fe₁₇H₃ and Er₂Fe₁₇H₃. Hydrogenation induces a FOMP-type transition in the Ho₂Fe₁₇H₃ compound and, on the contrary, leads to the disappearance of the FOMP type transition in the Er₂Fe₁₇H₃ compound. The obtained results are discussed on the basis of a model based on the interaction of the quadrupolar moment and the magnetic moment of the 4f electron shell of the rare earth ion with the interstitial hydrogen. It is established that the orientation of the quadrupolar moment of the asymmetric 4f shell with respect to the direction of the resulting magnetic moment of 4f electrons plays an important role.     

Synthesis and structure of CsTi5Te8: Relation to the TlV5S8, TlCr3S5, and similar channel structures

The compound CsTi₅Te₈ was obtained as a crystalline product by an “U-assisted” reaction of Cs, Ti, U, and Cs₂Te₃ in a CsCl flux at 1173 K. The structure of CsTi₅Te₈ contains a three-dimensional network of face-sharing and edge-sharing TiTe₆ octahedra that form one-dimensional channels. The Cs⁺ cations reside in channels that propagate in the [0 1 0] direction. The structure is closely related to several other types of channel structures including those of the minerals of the hollandite and psilomelane families, and those of the TlV₅S₈ and TlCr₃S₅ structure types.