Disproportionation in Hydrogen and Recombination of the Laves Phases of Zirconium with Chromium

By the methods of differential thermal, X-ray phase diffraction, and metallographic analyses, we study the processes of conventional and solid HDDR (hydrogenation-disproportionation-desorption-recombination) in ZrCr₂ compound with C14- and C15-type structures under initial pressures of hydrogen of 3 and 5 MPa at temperatures of up to 1243°K. The ZrCr₂ compound with C15-type structure disproportionates at 1048 and 1093°K for P _H2 = 5 and 3 MPa into ZrH _x and Cr and recombines in a vacuum. The temperature of disproportionation of the Laves phase with C15-type structure is lower than for the C14 phase by 120°K. As the pressure of hydrogen increases, the temperature of disproportionation decreases. The application of HDDR to the reconstruction of the C14-type structure of the Laves phase in ZrCr₂ into the C15-type structure makes it possible to decrease the temperature of treatment and its duration as compared with the case of annealing in vacuum. The procedure of HDDR forms a nanostructure in ZrCr₂. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 3, pp. 101–108, May–June, 2005.     

Sorption and desorption of hydrogen in the alloys based on the ErNi<Subscript>2</Subscript> compound

We study the process of formation of pseudobinary Laves phases on the basis of the ErNi₂ compound realized as a result of the substitution of Y for Er and V for Ni and determine the hydrogen-sorption properties of these phases. The crystal structures of the original compounds and their saturated hydrides are investigated by the X-ray diffraction method. It is shown that these compounds absorb hydrogen under a pressure of 0.1–0.12 MPa without amorphization. The maximum hydrogen-sorption capacity (3.4 at. H/f.u.) is obtained for the Er_0.85Y_0.15Ni₂ compound. The thermal stability of hydrides is determined by the method of thermodesorption spectroscopy in gaseous hydrogen at a heating rate of 5°C / min. An insignificant substitution o Y for Er and V for Ni improves the parameters of hydrogen sorption and desorption for these compounds. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 5, pp. 76–80, September–October, 2007.     

Influence of Titanium on Hydrogen-Induced Transformations in the Laves Phases Based on Zirconium

By the methods of differential thermal, and X-ray phase analyses, we study the influence of hydrogen (hydrogenation, disproportionation, desorption, and recombination) on the phase transformations in Zr_{1 − x} Ti_xCr₂ (x = 0.1 and 0.2) alloys under a pressure of hydrogen of 5 MPa at temperatures varying from the room temperature to 1238°K. For 3–5 MPa and 1163–1223°K, we observe the decomposition of the Laves phase with C14-type structure accompanied by the formation of Zr_{1 − x} Ti_xCr₂H_y and ZrH_x hydrides and Cr. Under a pressure of 5 MPa, on holding at 1223°K for more than 4 h, the compounds completely disproportionate into zirconium and titanium hydrides and chromium. On holding in a vacuum at 1193– 1238°K, the compounds recombine into the phases with C14- or C15-type structure or their mixture.__________Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 40, No. 6, pp. 67–72, November–December, 2004.     

Thermodynamic stability of the GaN-InN-AlN system

Based on the regular-solution approximation and the Stringfellow approach, in which the intermolecular interaction in multicomponent systems is considered to be determined by the difference in the lattice parameters, the interaction parameter of ternary III-V-based solid solutions is expressed through the difference in the lattice parameters of the binary constituents. For the GaN-InN, GaN-AlN, and AIN-InN pseudobinary systems, the interaction parameters are determined and the binodals and spinodals are calculated. In the Ga_xIn_yAl_1-x-y N solid-solution system, the spinodal isotherms are mapped out.     

Hydrides of substituted derivatives based on the YNi<Subscript>3</Subscript> compound

The crystallographic characteristics of YNi_3−x Mn_x pseudobinary compounds are determined by the methods of X-ray diffraction analysis. It is shown that the partial substitution of nickel for manganese occurs mainly in the layers with CaCu₅-type structure but not in the layers with Mg Zn₂-type structure, as was reported for A₃B₈X compounds. All synthesized samples are efficient absorbers of hydrogen and their hydrogen-absorption capacity monotonically decreases as the concentration of the alloying element increases. At the same time, this type of alloying substantially decreases the absorption-desorption pressure of hydrogen, which makes the developed alloys quite promising as hydrogen-storage materials. All investigated materials have good charging-discharging characteristics in KOH solutions. The best electrochemical parameters are observed for the Y Ni_2.67Mn_0.33 alloy (C _max = 305 mA · h/g). __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 4, pp. 47–52, July–August, 2007.     

Canonic-Like HER Activity of Cr1–xMoxB2 Solid Solution: Overpowering Pt/C at High Current Density

Abundant transition metal borides are emerging as substitute electrochemical hydrogen evolution reaction (HER) catalysts for noble metals. Herein, an unusual canonic-like behavior of the c lattice parameter in the AlB₂-type solid solution Cr_1–xMo_xB₂ (x = 0, 0.25, 0.4, 0.5, 0.6, 0.75, 1) and its direct correlation to the HER activity in 0.5 M H₂SO₄ solution are reported. The activity increases with increasing x, reaching its maximum at x = 0.6 before decreasing again. At high current densities, Cr_0.4Mo_0.6B₂ outperforms Pt/C, as it needs 180 mV less overpotential to drive an 800 mA cm⁻² current density. Cr_0.4Mo_0.6B₂ has excellent long-term stability and durability showing no significant activity loss after 5000 cycles and 25 h of operation in acid. First-principles calculations have correctly reproduced the nonlinear dependence of the c lattice parameter and have shown that the mixed metal/B layers, such as (110), promote hydrogen evolution more efficiently for x = 0.6, supporting the experimental results.     

Hydrogen activation of LaNi5: Implications of fracture mechanisms on hydriding properties

The fracture mechanisms of two different LaNi₅ alloys (A and B) have been investigated during the first few hydrogen loading/unloading cycles that constitute activation of this material. The principal difference between the two formulations was the presence of Nideficient planar inclusions, oriented perpendicular to the crystallographicc-axis, in alloy A. Both types were found to fracture at high loadings of hydrogen (hydrogen-to-metal ratios of ca. 1) during the activation cycle, as a result of the differential expansion between the microdomains of the -and -hydride phases. However, alloy A also fractured at an earlier stage in the activation cycle, at very low hydrogen-to-metal ratios (0.06), by delamination at the planar inclusion boundaries. This had the effect of reducing the hysteresis during the first activation cycle, most probably due to faster kinetics. The implication is that the hydrogen storage properties of the alloy can be tailored by microstructural design.     

Ab initio study of stacking faults and deformation mechanism in C15 Laves phases Cr2X (X = Nb,Zr, Hf)

Based on the synchroshear model, the formation of stacking fault and twinning fault in C15 Laves phases is modeled, then the generalized stacking fault energy curves and deformation mechanism in C15 Laves phases Cr₂X (X = Nb, Zr, Hf) alloys are investigated by ab initio calculations based on the density functional theory. The results demonstrate that the unstable stacking fault and twinning fault energies of C15 Laves phases Cr₂X (X = Nb, Zr, Hf) by the synchroshear are still large while the stable stacking fault and twinning fault energies are low, and the deformation modes by extended partial dislocation and twining are feasible in C15 Laves phases Cr₂X (X = Nb, Zr, Hf). Moreover, the Cr₂Nb has the largest deformation twinning tendency, followed by Cr₂Zr and Cr₂Hf. The evolution of electronic structure during the synchroshear process is further studied to unveil the intrinsic mechanism for the formation of stacking fault and twinning fault in C15 Laves phases Cr₂X (X = Nb, Zr, Hf).     

Dual Properties of Microwave Absorption and Thermal Protection in La0.5Sr0.5FeO3–Al2O3 Pseudobinary Composites

As multifunctional material for microwave absorption and thermal protection, the dielectric and thermophysical properties of equilibrium phases in LSF(La_0.5Sr_0.5FeO₃)–Al₂O₃ pseudobinary phase diagram are investigated herein. Four pseudobinary composites are obtained by sintering at 1400 °C for 10 h with different raw components (x wt% LSF-(100−x) wt% Al₂O₃, x = 20, 40, 60 and 80), labeled as LSFA20, LSFA40, LSFA60, and LSFA80, respectively. After sintering, the main equilibrium phase in LSFA20 and LSFA40 composites is SrAl₁₂O₁₉-based solid solution. For LSFA60 and LSFA80, however, LSF-based and SrAl₁₂O₁₉-based solid solutions are the main equilibrium phases. The increase of conductive LSF content results in the highest dielectric loss tangent and the best microwave absorbing property in LSFA80, in which the bandwidths for reflection loss less than −10 and −5 dB are about 2.37 and 7.7 GHz, respectively, when the thickness is only 1.5 mm. The thermophysical properties reveal that the thermal conductivity in LSF-Al₂O₃ pseudobinary composites shows weak temperature dependence because of the opposite contribution between phonons and electrons. It is lower than that of the traditional thermal barrier coating material of 8 wt% Y₂O₃-stabilized zirconia (8YSZ).     

Constitution,structure and magnetic properties of some rare-earth-cobaltaluminium alloys

The constitution and structure of the alloys represented by the formulae Ce_1–x Al _x Co₅ and Pr_1–x Al _x Co₅ (where 0x0.6) have been studied by X-ray diffraction and metallographic techniques. The substitution of between 1 and 3 at % Al (0.06x0.18) for Ce in CeCo₅ produces a mixture of the 15 and 217 phases based on CeCo₅ and Ce₂Co₁₇; there are two variations of the 217 phase which are isostructural with the hexagonal Th₂Ni₁₇-type and rhombohedral Th₂Zn₁₇-type phases. At the composition Ce_0.76Al_0.24Co₅ (4 at% Al) the alloy consists only of the 217-type phases and metallographically the alloy is one phase in appearance. Further substitution of Al results in the precipitation of an fcc phase, based on the Co-Al solid solution, in the 217 matrix. The crystal structures of the Pr_1–x Al _x Co₅ alloys are very similar to those of the equivalent cerium alloys, although the ternary 217-type phase has only the rhombohedral structure, as does the binary Pr₂Co₁₇ phase. The metallographic structures of the Pr alloys in the composition range 1 to 3 at% Al show significant differences from the corresponding Ce alloys. Determination of the Curie temperatures of theR _1}-xAl _x Co₅ alloys (R= Ce and Pr) in the composition range 0x0.24 showed good agreement between the measured and published values for both the CeCo₅ and PrCo₅ phases. The Curie temperatures of the ternary 217-type phases were approximately 50 K and 70 K lower than those of the binary, Ce₂Co₁₇ and Pr₂Co₁₇ alloys, respectively.     

Investigation of Ba<Subscript>2-x</Subscript>Sr<Subscript>x</Subscript>TiO<Subscript>4</Subscript>: Structural aspects and dielectric properties

Investigation of solid solution of barium-strontium orthotitanates of the type, Ba_2-x Sr _x TiO₄ (0 ≤x≤ 2), show that pure phases exist only for the end members, Ba₂TiO₄ and Sr₂TiO₄, crystallizing in the β-K₂SO₄ and K₂NiF₄ structures, respectively. The intermediate compositions (till≥ 1) lead to a biphasic mixture of two Ba₂TiO₄-type phases (probably through a spinodal decomposition) with decreasing lattice parameters, indicating Sr-substitution in both the phases. Forx > 1, Sr₂TiO₄ along with a secondary phase is obtained. The dielectric constant and dielectric loss were found to decrease with Sr substitution till the nominal composition ofx = 1. However, pure Sr₂TiO₄ shows higher dielectric constant compared to the solid solution composition. Sr₂TiO₄ shows very high temperature stability of the dielectric constant.     

Phase equilibria in the system CaO-ZnO-B2O3 at 850°C

Phase equilibria in the system CaO-ZnO-B₂O₃ were investigated at 850°C using X-ray powder diffraction techniques. The binary phases reported previously were confirmed, but no ternary phases were found. Solid solution effects were investigated for the binary phases by comparison of the patterns, whereas for calcium oxide and zinc oxide, accurate lattice parameters were compared. No solid solutions were detected.     

Structure of deuterided NbVCo

A deuteride of composition NbVCoD_2.5 has been prepared at high deuterium pressures (up to P _{D 2} = 0.2 GPa), and the positions of the metal and D atoms in its structure have been determined by x-ray and neutron diffraction techniques. The deuteride has the same structure as NbVCo (hexagonal Laves phase structure), with the V and Co atoms occupying positions 2a and 6h (B site in AB₂) at random and the D atoms residing predominantly in positions 24l and 12k, typical of hydrogen in hexagonal Laves phases. This hydrogen distribution is due to the blocking of sites adjacent to those occupied by hydrogen.     

Synthesis and Determination of the Crystal Structure of Hydrides of Er(M,V)<Subscript>2</Subscript>, where M = Fe or Co,Compounds

We study the process of formation of the Laves phases AB₂ in Er(M, V)₂ (M = Fe or Co) systems and determine their hydrogen-sorption properties. The crystal structure of parent compounds and their saturated hydrides is analyzed by the X-ray diffraction method. It is shown that these compounds absorb hydrogen at pressures of 0.1– 0.12 MPa without amorphization. The formation of the ErFe₂ hydride is accompanied by the transformation of a cubic MgCu₂-type structure into a trigonal TbFe₂-type structure. Even an insignificant substitution of Fe with V or Co leads to an increase in the hydrogen-sorption capacity and prevents the changes in the crystal structure.__________Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 40, No. 6, pp. 62–66, November–December, 2004.     

Nanoscale structure and atomic disorder in the iron-based chalcogenides

The multiband iron-based superconductors have layered structure with a phase diagram characterized by a complex interplay of charge, spin and lattice excitations, with nanoscale atomic structure playing a key role in their fundamental electronic properties. In this paper, we briefly review nanoscale structure and atomic disorder in iron-based chalcogenide superconductors. We focus on the Fe(Se,S)_1−xTe_x (11-type) and K_0.8Fe_1.6Se₂ (122-type) systems, discussing their local structure obtained by extended x-ray absorption fine structure. Local structure studies on the Fe(Se,S)_1−xTe_x system reveal clear nanoscale phase separation characterized by coexisting components of different atomic configurations, similar to the case of random alloys. In fact, the Fe–Se/S and Fe–Te distances in the ternary Fe(Se,S)_1−xTe_x are found to be closer to the respective distances in the binary FeSe/FeS and FeTe systems, showing significant divergence of the local structure from the average one. The observed features are characteristic of ternary random alloys, indicating breaking of the local symmetry in these materials. On the other hand, K_0.8Fe_1.6Se₂ is known for phase separation in an iron-vacancy ordered phase and an in-plane compressed lattice phase. The local structure of these 122-type chalcogenides shows that this system is characterized by a large local disorder. Indeed, the experiments suggest a nanoscale glassy phase in K_0.8Fe_1.6Se₂, with the superconductivity being similar to the granular materials. While the 11-type structure has no spacer layer, the 122-type structure contains intercalated atoms unlike the 1111-type REFeAsO (RE = rare earth) oxypnictides, having well-defined REO spacer layers. It is clear that the interlayer atomic correlations in these iron-based superconducting structures play an important role in structural stability as well as superconductivity and magnetism.     

Zr1-xTix(Ni0.6Mn0.3V 0.1Cr0.05)2(x=0～0.5)Laves相储氢合金的电化学性能

本文研究Zr1-xTix(Ni0.6 Mn0.3V0.1Cr0.05)2(x=0,0.1,0.2,0.3,0.4,0.5)系Lav es相储氢电极合金的气态P-C-T性能、晶体结构及电化学性能.XRD分析表明,Ti合金化使 Zr基储氢合金主相从C15相转变为C14相.当x>0.2时,第二相Zr7Ni10相消失, 并出现TiNi相.Ti合金化使Zr基储氢合金中C15相和C14相的晶格常数线性递减.气态P-C-T 测试表明,Ti合金化从x=0增加至x=0.5时合金的吸放氢平台压力升高约10倍,但降低了储氢合金的最大储氢容量.电化学测试表明,Ti合金化有利于改善Zr基储氢合金的活化性能, 这与Ti在KOH溶液中易于溶解有关,但过高的Ti含量降低了合金电极的循环稳定性.Zr1 -xTix(Ni0.6Mn0.3V0.1Cr0.05)2合金的电化学容量和高倍率放电性能均随合金中Ti含量的增加先上升后下降,这与合金的相结构组成有很大关系 .     

Phase equilibria in the high magnesia corner of the system MgO-ThO2-B2O3 at 1200° C

Phase equilibria in the high magnesia corner of the system MgO-ThO₂-B₂O₃ were investigated at 1200°C using X-ray powder diffraction techniques. The two magnesium borates reported previously at this temperature were confirmed, but no magnesium thorate and no ternary phases were found. Solid solution effects were investigated; for the binary phases by comparison of patterns, for magnesium oxide and thorium oxide by comparison of lattice parameters. No solid solutions were detected.Phase equilibria in the system MgO-ThO₂ were investigated at 1500°C, again no binary compound was found and no solid solution detected. A suggestion is made to reconcile the latter observation with previous work.     

Investigation of phase formation of RFe11V1 ? xTix (R = Pr, Ce) compounds

Phase formation of PrFe₁₁V_{1 – x}Ti_x and CeFe₁₁V_{1 – x}Ti_x compounds with the ThMn₁₂-type structure has been investigated by x-ray diffraction (XRD), differential thermal analysis (DTA) and ac initial susceptibility. The stable temperature range of the 1-12 phase for PrFe₁₁V_{1 – x}Ti_x alloys has been constructed as a function of Ti content. It is found that the PrFe₁₁V compound with the ThMn₁₂-type structure do not form. The PrFe₁₁Ti compound with the ThMn₁₂-type structure can only be obtained by annealing at a narrow temperature range between 1030 °C and 1113 °C. Furthermore, 1-12 phase can be obtained at lower temperature and wider temperature range with decreasing Ti content x(0.2 x 1). The CeFe₁₁V and CeFe₁₁Ti compound with ThMn₁₂-type structure can be synthesized, and it is more favorable to synthesis the 1-12 single phase for the pseudotenary CeFe₁₁V_{1 – x}Ti_x compounds. For PrFe₁₁V_{1 – x}Ti_x compounds with x = 0.2–1, the lattice parameters a and c do not vary very much: around 0.860 and 0.479 nm, and Curie temperature T_c is 268 °C–329 °C. For CeFe₁₁V_{1 – x}Ti_x compounds the lattice parameters a and c are around 0.857 and 0.478 nm, and Curie temperature T_c is 211 °C–252 °C.     

Electronic band structure and stability of fluorite-like phases in the Mg-Sn-B system

Self-consistent FLMTO-GGA calculations are used to analyze the electronic states and energy bands in cubic fluorite-like (Mg₂Sn, “Mg₂B,” Mg₂SnB_x) and hexagonal (MgB₂) phases of the Mg-Sn-B system. Their electronic structure and chemical bonding are discussed, and their equilibrium lattice parameters, bulk moduli, and the derivatives of their bulk moduli are determined. According to the calculated energies of formation, the stability of the phases in question decreases in the order MgB₂ > Mg₂Sn > “Mg₂B” > Mg₂SnB. The positive energies of formation of Mg₂SnB and “Mg₂B” suggest that the synthesis of these phases from elements (Mg, Sn, and B) under equilibrium conditions is unlikely.     

Magnetic hysteresis and crystallization studies on metallic glass alloy Fe67Co18B14Si1

Magnetic hysteresis studies were carried out on Metglas 2605 Co(Fe₆₇Co₁₈B₁₄Si₁) samples, cut parallel and perpendicular to the ribbon axis and annealed at different temperatures. The samples annealed at 450°C for 2 hr show a coercive force of 8·75 Oe and 0·60 Oe in the parallel and perpendicular directions respectively. Electron probe micro analysis studies revealed the onset of primary crystallization at 400°C and a gradual displacement of B and Si from the lattice as the annealing temperature was increased to 450°C. The observed large coercive force is due to an increase in anisotropy resulting from an intergrowth pattern of the type Fe _x Co_{1 −x} , 0·3<x<1·0, including boron containing phases such as (FeCo)B, (FeCo)₂B, (FeCo)₃B, developed by the displacement of and Si from the original amorphous lattice.