Ni-based Compounds Research Articles

Porous nickel oxide pseudo-capacitive materials fabricated by Ni-Schiff base nanostructures template

Three nanoscale Ni-Schiff-base coordination polymer particles have been firstly prepared in poor solvent (DMF) through a precipitation method. XRD, TGA and EA results show that as-synthesized compounds are either amorphous or crystalline. High temperature annealing of these Ni-based compounds can result in pseudo-capacitive NiO electrodes. Series of electrochemical measurements illustrated that the as-prepared NiO material, especially for NiO nanospheres could deliver a maximum specific capacitance of 153Fg−1 and good stability over 1000 cycles with the capacitance retention of 100%, indicating the morphology and resistance effect on the diffusion-controlled redox reaction between the OH− ions and the NiO samples.

In Situ Observation of Active Oxygen Species in Fe-Containing Ni-Based Oxygen Evolution Catalysts: The Effect of pH on Electrochemical Activity.

Ni-based oxygen evolution catalysts (OECs) are cost-effective and very active materials that can be potentially used for efficient solar-to-fuel conversion process toward sustainable energy generation. We present a systematic spectroelectrochemical characterization of two Fe-containing Ni-based OECs, namely nickel borate (Ni(Fe)-B(i)) and nickel oxyhydroxide (Ni(Fe)OOH). Our Raman and X-ray absorption spectroscopy results show that both OECs are chemically similar, and that the borate anions do not play an apparent role in the catalytic process at pH 13. Furthermore, we show spectroscopic evidence for the generation of negatively charged sites in both OECs (NiOO(-)), which can be described as adsorbed "active oxygen". Our data conclusively links the OER activity of the Ni-based OECs with the generation of those sites on the surface of the OECs. The OER activity of both OECs is strongly pH dependent, which can be attributed to a deprotonation process of the Ni-based OECs, leading to the formation of the negatively charged surface sites that act as OER precursors. This work emphasizes the relevance of the electrolyte effect to obtain catalytically active phases in Ni-based OECs, in addition to the key role of the Fe impurities. This effect should be carefully considered in the development of Ni-based compounds meant to catalyze the OER at moderate pHs. Complementarily, UV-vis spectroscopy measurements show strong darkening of those catalysts in the catalytically active state. This coloration effect is directly related to the oxidation of nickel and can be an important factor limiting the efficiency of solar-driven devices utilizing Ni-based OECs.

Standard enthalpies of formation of selected Ni2YZ Heusler compounds

The standard enthalpies of formation (ΔfH°) of selected ternary Ni-based Heusler compounds Ni2YZ (Y = Co, Cu, Fe, Hf, Mn, Ti, V; Z = Al, Ga, In, Si, Ge, Sn) were measured using high temperature direct reaction calorimetry. The measured standard enthalpies of formation (in kJ/mole of atoms) of the Heusler structured (L21, prototype Cu2MnAl, Pearson symbol cF16, space group Fm3(_) m) compounds are: Ni2MnGa (−29.8 ± 3.9); Ni2MnIn (−24.5 ± 2.0); Ni2MnSn (−29.7 ± 2.9); Ni2TiGa (−42.5 ± 2.2); Ni2TiIn (−28.5 ± 1.1); Ni2TiSn (−46.8 ± 2.0), for the B2 compound (prototype CsCl, Pearson cP2, space group Pm3(_) m): Ni2MnAl (−32.0 ± 2.8), for the inverse Heusler structured (i-L21, prototype Li2AgSb, Pearson symbol cF16, space group F4(_) 3 m) compound: Ni2CuSn (−12.5 ± 2.1), for the compounds of the L12 (prototype AuCu3, Pearson symbol cP4, space group Pm3(_) m) structure: Ni2CuAl (−38.9 ± 3.1); Ni2FeGe (−25.8 ± 3.0). Several off-stoichiometric alloys in the Ni–Mn–Sn system were also investigated: Ni0.55Mn0.20Sn0.25 (−26.6 ± 1.0); Ni0.45Mn0.30Sn0.25 (−27.5 ± 2.6); Ni0.40Mn0.35Sn0.25 (−26.6 ± 2.6); Ni0.25Mn0.50Sn0.25 (−20.9 ± 2.6); Ni0.50Mn0.30Sn0.20 (−21.0 ± 3.2); Ni0.50Mn0.35Sn0.15 (−20.1 ± 1.7). Values are compared with those from first principles calculations in published papers and the Open Quantum Materials Database (OQMD). Lattice parameters were determined using X-ray diffraction analysis. Microstructures were characterized using scanning electron microscopy (SEM) with an energy dispersive spectrometer (EDS). Differential scanning calorimetry (DSC) was used to measure the melting points of the compounds.

Ab initio study of Fermi surface and dynamical properties of Ni2XAl (X = Ti, V, Zr, Nb, Hf and Ta)

A detailed study on the pressure and temperature effects on ternary Ni-based inter-metallic compounds Ni2XAl (X=Ti, V, Zr, Nb, Hf and Ta) have been carried out using density functional theory. The calculated ground state properties are in good agreement with experiments for all the investigated compounds. The band structures and Fermi surface topology is found to be quite similar for all the compounds except for Ni2NbAl, where we find an extra band to cross the Fermi level under compression resulting in a new electron pocket at X-point. Ni2NbAl is found to be a superconductor with superconducting transition temperature of 3.1K which agrees quite well with the experimental value and the calculated Tc is found to vary non-monotonically under pressure. From the calculated phonon dispersion relation, we find all the investigated Ni-based Heusler compounds to be dynamically stable, until high pressure. The ductile nature of these compounds is confirmed from the calculated Cauchy’s pressure, Pugh’s ratio and Poisson’s ratio. In addition, the thermodynamic properties show Ni2TiAl to have lower specific heat and entropy but higher internal energy and free energy among all the investigated compounds.

Homochiral Cu(II) and Ni(II) malates with tunable structural features

Four new homochiral metal–organic frameworks (MOFs) based on S-malate anions and N-donor linkers of different length have been prepared under solvothermal conditions. [Cu(mal)(bpy)]·H2O (1), [Cu(mal)(bpe)]·2H2O (2), [Ni(mal)(bpy)]·1.3CH3OH (3) and [Ni(mal)(bpe)]·4H2O (4) (mal=S-malate, bpy=4,4′-bipyridil, bpe=trans-1,2-bis(4-pyridyl)ethylene) were characterized by a number of analytical methods including powder X-ray diffraction, elemental, thermogravimetric analyses, IR spectroscopy. Compounds 1–3 were structurally characterized by X-ray crystallography. The absence of the chiral ligand racemization under synthetic conditions was unambiguously confirmed by polarimetry experiments. Compounds 1 and 2 contain metal-malate layered motives, connected by N-donor linkers and contribute to the family of isoreticular Cu(II) malates and tartrates [Cu(mal)L] and [Cu(tart)L], (tart=tartrate; L=ditopic rigid organic ligand). The Ni-based compounds 3 and 4 share 1D chiral {Ni(mal)} motives and possess novel type of the chiral framework, previously unknown for chiral carboxylates. The linear N-donor linkers connect these chiral chains, thus controlling the channel diameter and guest accessible volume of the homochiral structure, which exceeds 60 %.

Itinerant electron magnetism of η-carbides Co6M6C and Ni6M6C (M = Mo and W)

Magnetic, transport, and thermal properties of metallic η-carbides Co6M6C and Ni6M6C (M=Mo and W) with the cubic Ni6Mo6C-type structure have been characterized. The Ni-based compounds Ni6Mo6C and Ni6W6C are Pauli paramagnets with temperature-independent susceptibilities. Susceptibilities of the Co-based compounds Co6Mo6C and Co6W6C are enhanced and temperature-dependent. Co6Mo6C remains paramagnetic down to the lowest temperature, while Co6W6C undergoes an antiferromagnetic-type transition at 46K. A metamagnetic transition was observed for Co6W6C at 20–30T at the lowest temperatures. The correlation among the enhancements in the susceptibility, the resistivity, and the electronic specific heat suggests the presence of moderate electron correlation in these compounds.

Superconductivity of the Ni-based ternary compounds with AlB2-type structure Y2NiGe3 and La2NiGe3

The crystal structure, electrical, and magnetic properties of the Ni-based ternary compounds Y2NiGe3 and La2NiGe3 have been investigated. Powder X-ray diffraction patterns reveal that both compounds crystallize in the AlB2-derived hexagonal structure with values of the lattice parameters a=4.066(7)Å and c=4.025(1)Å for Y2NiGe3 and a=4.180(2)Å and c=4.334(1)Å for La2NiGe3. A sudden drop to zero value in the ρ(T) curves and the diamagnetic behavior observed in the χac(T) curves conform the occurrence of bulk superconductivity in Y2NiGe3 and La2NiGe3 with TC of 0.553K and 0.394K, respectively. Band structure calculations reveal that superconductivity in these two compounds is most probably from Y 4d electrons and La 5d electrons, respectively.

Research Progress on Ni-Based Antiperovskite Compounds

The superconductivity in antiperovskite compound MgCNi3was discovered in 2001 following the discovery of the superconducting MgB2. In spite of its lower superconducting transition temperature (8 K) than MgB2(39 K), MgCNi3has attracted considerable attention due to its high content of magnetic element Ni and the cubic structure analogous to the perovskite cuprates. After years of extensive investigations both theoretically and experimentally, however, it is still not clear whether the mechanism for superconductivity is conventional or not. The central issue is if and how the ferromagnetic spin fluctuations contribute to the cooper paring. Recently, the experimental results on the single crystals firstly reported in 2007 trend to indicate a conventionals-wave mechanism. Meanwhile many compounds neighboring to MgCNi3were synthesized and the physical properties were investigated, which enriches the physics of the Ni-based antiperovskite compounds and help understand the superconductivity in MgCNi3. In this paper, we summarize the research progress in these two aspects. Moreover, a universal phase diagram of these compounds is presented, which suggests a phonon-mediated mechanism for the superconductivity, as well as a clue for searching new superconductors with the antiperovskite structure. Finally, a few possible scopes for future research are proposed.

The stable CaBe 2Ge 2 structures in antimonide compounds ATM 2Sb 2 (A = Ca, Sr, Ba; TM = Fe, Co, Ni, Cu): A first-principles study

We have investigated the structural properties of 3d transition metal antimonide compounds ATM 2Sb 2 by first-principles calculations. We find that the calcium-based CaNi 2Sb 2, the strontium-based SrNi 2Sb 2, SrCu 2Sb 2, and the barium-based BaCu 2Sb 2 are stable in the CaBe 2Ge 2-type structure. All the other compounds are stable in the ThCr 2Si 2-type structure. SrCo 2Sb 2 in the ThCr 2Si 2-type structure has specifically ferromagnetic preference. The stable compounds in the CaBe 2Ge 2-type structure have strong interlayer interactions. Although the stable stacking structures are different, all the Fe-based compounds have the stripe-like antiferromagnetic ground states. The Co-based compounds have the ferromagnetic ground states. The Ni-based and Cu-based compounds have the nonmagnetic ground states.

The effect of ionization and CH3 ligand for hydrogen storage in Co- and Ni-based organometallic compounds

Maximum capacities of the hydrogen storage in organometallic compounds consisting of Co and Ni atoms bound to CmHm ring (m = 4, 5; capped type) were, respectively, found as 3.48 and 3.49 wt % (Guo et al., Struct Chem, 2009, 20, 1107). Here, we extend this study to structures having a transition metal (TM) inserted in CmHm ring (inserted type), having TM located on either a C4H or a C5H molecule, and the CH3 ligand bound to the organometallic compounds. We find that for the CoC4H4 and NiC4H4 complexes, the capped types are 1.39 eV and 1.41 eV higher in energy than the inserted types, respectively, while the ground states for CoC5H5 and NiC5H5 complexes are found to be the capped type, which are lower than the inserted types, respectively, by 1.27 eV and 1.31 eV. The maximum capacity of hydrogen storage reached 5.13 wt % for both of CoC4H(H2)3 complex and the inserted-type CoC4H4(H2)3 complex with a reasonable binding energy (0.3–1.0 eV per H2). The positively charged C4H4 and C5H5 molecules do not only improve the capacity of hydrogen storage but also make all H2 adsorbing in molecular form and keep the adsorption energy in an ideal range. After adding the CH3 ligand to the compounds, the average adsorption energy of H2 decreased to an ideal range 0.61–0.94 eV per H2 and the stability of the compounds is also improved. Finally, we analyze the HOMO–LUMO gaps and display the kinetic stability when H2 was added to organometallic compounds. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010

Nickel assisted sintering of Ti 3SiC 2 powder under pressureless conditions

This investigation was aimed to study the effect of nickel addition on the sintering behaviour of Ti 3SiC 2 powder under pressureless conditions. Nearly pure bulk Ti 3SiC 2 ceramic with relative density of ∼98.5% was produced at 1500 °C by sintering of Ti 3SiC 2 powder while using 1 wt.% nickel as a sintering aid. The activation energy of sintering of Ti 3SiC 2 powder was determined to be 351 ± 5 kJ/mol, which was decreased slightly to 305 ± 10 kJ/mol when nickel (1 wt.%) was added. Sintering of Ti 3SiC 2 powder was found to be controlled by mixed mode of mechanisms, i.e., the interface reactions and diffusion of Si atoms. The mechanism was changed to liquid phase sintering due to melting of Ni-based compounds in the sample sintered with Ni. The reaction of Ni with Ti 3SiC 2 helped to decrease the grain growth rate. The hardness (Vickers), flexural strength and fracture toughness of the sintered Ti 3SiC 2–1Ni sample were found to be 3.4 GPa, 311 ± 22 MPa and 2.8–6.4 MPa m 1/2, respectively.

Thermoelectric power in (, Ni; , Ga) compounds

Abstract CeCu4In and CeCu4Ga compounds belong to heavy fermion (HF) systems. CeNi4In and CeNi4Ga seems to be on the border between HF and mixed-valence (MV) states. It has been observed that thermoelectric power (TEP) shows a significant difference between these Cu and Ni-based compounds, whereas thermal conductivity does not reveal such dramatic changes in the temperature dependencies. These results are analyzed assuming the Kondo effect at presence of the crystal electric field for the HF compounds and two density of states peaks in the region of the Fermi level for the remaining compounds. The details of the electronic structure are supposed to be responsible for the negative TEP of CeNi 4 M .

Hydrogen binding property of Co- and Ni-based organometallic compounds

The binding property of hydrogen on organometallic compounds consisting of Co, and Ni transition metal atoms bound to CmHm rings (m = 4, 5) is studied through density functional theory calculation. CoCmHm and NiCmHm complexes can store up to 3.49 wt% hydrogen with an average binding energy of about 1.3 eV. The adsorption characteristics of hydrogen to organometallic compounds are investigated by analyzing vibrational spectra of CoC4H4(H2)n and NiC4H4(H2)n (n = 0, 1, 2). The kinetic stability of these hydrogen-covered organometallic complexes is assured by analyzing the energy gap between the highest occupied molecular orbitals and the lowest unoccupied molecular orbitals. It is also discussed the application of 18-electron rule in predicting maximum number of hydrogen molecules that could be adsorbed by these organometallic compounds.

Ni 2X 2 (X = pnictide, chalcogenide, or B) based superconductors

We review the properties of Ni-based superconductors which contain Ni 2X 2 (X = As, P, Bi, Si, Ge, B) planes, a common structural element found also in the recently discovered FeAs superconductors. Strong evidence for the fully gapped nature of the superconducting state has come from field dependent thermal conductivity results on BaNi 2As 2. Coupled with the lack of magnetism, the majority of evidence suggests that the Ni-based compounds are conventional electron–phonon mediated superconductors. However, the increase in T c in LaNiAsO with doping is anomalous, and mimics the behavior in LaFeAsO. Furthermore, comparisons of the properties of Ni- and Fe-based systems show many similarities, particularly with regards to structure–property relationships. This suggests a deeper connection between the physics of the FeAs superconductors and the related Ni-based systems which deserves further investigation.

IsomorphousPrT2B2C(T=Co,Ni,Pt)single crystals: Structural, transport, and magnetic properties

The full substitution of Ni by Co and Pt enclosed in the same crystalline structure $(I4∕mmm)$ of Pr-based compounds have been investigated. The structural characteristics, magnetic properties, and magnetoresistance of $\mathrm{Pr}{\mathrm{Co}}_{2}{\mathrm{B}}_{2}\mathrm{C}$, $\mathrm{Pr}{\mathrm{Ni}}_{2}{\mathrm{B}}_{2}\mathrm{C}$, and $\mathrm{Pr}{\mathrm{Pt}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ single crystals were studied to determine the reason for the absence or presence of superconductivity in those compounds. An antiferromagnetic transition was found for $\mathrm{Pr}{\mathrm{Co}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ at about $8.5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, where the easy magnetization axis is along the $c$-crystallographic direction whereas in $\mathrm{Pr}{\mathrm{Ni}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ the easy magnetization was at the $ab$ plane. In $\mathrm{Pr}{\mathrm{Ni}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ a small magnetization without traces of saturation is found when it is measured up to $18\phantom{\rule{0.3em}{0ex}}\text{Tesla}$ of applied magnetic field. This behavior suggests a screening effect as a result of a moderate hybridization between the conduction band and Pr ions. Superconductivity occurs in $\mathrm{Pr}{\mathrm{Pt}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ at about $6\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The Pt-Pt distance and internal bonding angles are similar to those observed in the superconducting Ni-based compounds. Magnetoresistance measurements show positive and quadratic behavior $(\ensuremath{\Delta}\ensuremath{\rho}∕{\ensuremath{\rho}}_{0}\ensuremath{\sim}a{H}^{2})$ suggesting a spin fluctuation system. In the $\mathrm{Pr}{\mathrm{Pt}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ compound the electronic mean free path is smaller than the BCS coherence length $(\ensuremath{\iota}⪡\ensuremath{\epsilon})$ suggesting a dirty type II superconductor.

Ni基GCP金属間化合物の積層構造と相安定性

Ni基GCP金属間化合物の積層構造と相安定性

Study of changes in L32 EELS ionization edges upon formation of Ni-based intermetallic compounds.

EELS L32 ionization edges in several Ni-based intermetallic compounds have been studied and interpreted in terms of the distribution of electrons in the valence d-bands. It is demonstrated that the integral EELS cross-sections change only slightly upon the formation of intermetallic compounds and therefore the charge transfer between atoms is negligible. On the other hand, the changes in the fine energy-loss near-edge structure (ELNES) of the Ni L3 edge can be readily detected indicating an important redistribution of d-electrons at the Ni site with alloying. These features are well reproduced by ab-initio calculations with a FLAPW method in its WIEN97 implementation. In contrast to the drastic effect of chemical environment, structural transformations in the investigated intermetallics result in smaller ELNES changes, which can be detected by only exceptional instruments with a higher energy resolution.

New 4234-type Intermetallic Borocarbides: Synthesis, Structure, and Magnetic Properties

New 4234-type compounds, structurally related to the n=4 member of the (LnC)nNi2B2 homologous series of intermetallic borocarbides, were synthesized by arc-melting. Here we report that this structure type, previously observed only for Ni-based compounds, can be synthesized for a large number of transition elements. Further, we find it to be stable for medium through small lanthanides. The compounds have formulas Y4T2B3C4 [T=Fe, Co, Ni, Ru, Rh, and Ir], Ln4T2B3C4 [Ln=Er, Dy, and Gd; T=Fe and Co], Lu4Ni2B3C4, and Sc4Ni2B3C4. The unit cells are pseudo-tetragonal, with lattice parameters ranging from a=3.348(1) Å, c=25.90(1) Å for Sc4Ni2B3C4 to a=3.624(1) Å, c=26.63(1) Å for Y4Rh2B3C4. Structural investigation by exit-wave reconstruction is reported, showing the presence of twinning on the unit cell scale. The phases show either Curie– Weiss behavior with very small magnetic moments per transition metal atom or temperature-independent paramagnetism.

Structural and chemical effects onEELSL3,2ionization edges inNi−basedintermetallic compounds

EELS ${L}_{3,2}$ ionization edges in several Ni-based intermetallic compounds have been studied and interpreted in terms of the distribution of electrons in the valence d bands. It is demonstrated that the integral EELS cross sections change only slightly upon the formation of intermetallic compounds and, therefore, the charge transfer between atoms is negligible. On the other hand, changes in the energy loss near edge fine structure (ELNES) of the Ni ${L}_{3}$ edge can be readily detected, indicating an important redistribution of d electrons at the Ni site. Full-potential linearized augmented-plane-wave calculations of the density of states (DOS) and simulations of the Ni ${L}_{3}$ edge EELS profiles show that these changes correspond to a hybridization between the Ni d band and d bands of the alloying elements. In contrast, structural transformations in the investigated intermetallic compounds do not significantly affect the ELNES as the typical energy resolution of EELS is not sufficient to track the slight difference in the DOS between various structural modifications of intermetallic compounds.

An XPS and AES study of the free corrosion of Cu-, Ni- and Zn-based alloys in synthetic sweat

This paper deals with the investigations into the behaviour during free corrosion of Cu/Zn/Ni, Cu/Ni/Zn and Ni/Cu alloys in a synthetic sweat medium by means of surface analyses. For the three alloys studied, our experimental results indicate the presence of a corrosion layer, the thickness of which increases with the increase of the copper content of the alloy. The corrosion layers are composed of Cu- and Ni-based compounds. For the alloys with a high Cu content, the latter is mainly composed of copper (I) oxide in which chloride anions are included. For the alloys with a high Ni content, Cu 2 (OH) 3Cl and Ni-compounds like Ni (OH) 2 and NiO are detected in the corrosion layer.