Intermetallic Nitrides Research Articles

Achieving Highly Durable Intermetallic PtMn3N Electrocatalyst via the Strong Metal‐N Bonds toward Oxygen Reduction Reaction

AbstractPt‐based intermetallic compounds have been considered promising electrocatalysts in the practical applications of fuel cells; however, the development of Pt‐based catalysts that meet performance targets of high activity, maximized stability, and low cost remains a huge challenge. Herein, an atomically ordered and low‐Pt intermetallic nitride (PtMn3N) catalyst are synthesized consisting of a strained Pt shell and PtMn3N core on carbon support via the KCl‐matrix protection strategy. The PtMn3N catalyst represents a high mass activity of 0.70 A mgPt−1 at 0.9 V and a specific activity degradation of 4.2% after 5000 potential cycles for the oxygen reduction reaction (ORR) in rotating disk electrode (RDE) testing, which substantially outperformed commercial Pt/C (0.25 A mgPt−1 and 17.4%). Density functional theory calculations reveal that the introduction of Mn elements to the Pt lattice is beneficial to produce appropriate compressive strain to weaken the binding energy of oxygen species and the introduction of N elements to promote the strong metal‐N interactions is conducive to alleviating the dissolution of metal atoms, allowing for displaying the prominent durability. This work provides an effective strategy of N‐doped Pt‐based intermetallic compounds to enhance the corrosion resistance of 3d transition metals and to enhance the ORR performance.

Zr-based Laves phases with nitride/hydride ions for ammonia synthesis

Early transition metal-based intermetallic compounds, such as ZrV2, ZrMn2, and ZrCr2, can reversibly absorb large amounts of hydrogen and are of great interest for hydrogen storage. The dissociative hydrogen chemisorption can proceed easily on the surface, allowing the rapid formation of intermetallic hydrides. In this study, we present the results of initial NH3 activity tests conducted on various Zr-based AB2-type intermetallic compounds, free of precious transition metals and rare earth metals. A dissociative hydrogen chemisorption together with nitrogen storage proceeds on AB2-type Laves phase intermetallic compounds accompanied by a lattice expansion. The formed intermetallic nitride hydride ZrCr2N0.4H1.4 exhibits stable catalytic activity as an ammonia synthesis catalyst.

Mn39Si9Nx: Epitaxial Stabilization as a Pathway to the Formation of Intermetallic Nitrides.

The realization of the full potential of nitrogen-containing solid-state materials is limited by the inert and gaseous nature of N2. In this Communication, we describe the simple synthesis yet complex structure of the new phase Mn39Si9Nx (x = 0.84). The formation of this intermetallic subnitride appears to be facilitated by the high solubility of nitrogen in manganese metal, while its structural features are guided by the complementary internal packing strains of Mn-Si and Mn-N domains, an effect known as epitaxial stabilization. These domains intergrow into a composite structure based on the interpenetration of tetrahedrally close-packed (TCP) and Mackay cluster-like modules. We anticipate that other systems combining nitrogen with the TCP packing of metals will be similarly driven toward intergrowth, opening a path to a broader family of intermetallic nitrides.

The effect of Al target current on the structure and properties of (Nb2Al)N films with an amorphous AlN phase

Nanocomposite films based on (Nb2Al)N intermetallic nitride have been obtained by the method of magnetron sputtering. X-ray diffraction analysis revealed two stable states of the crystalline structure: (i) NbN with low amount (within 5 at %) of dissolved Al in a composition close to (Nb2Al)N and (ii) an amorphous component related to aluminum nitride formed by reactive magnetron sputtering. The substructural characteristics (grain size and microdeformation level) are sensitive to the current via Al target and exhibit correlation with nanohardness and Knoop hardness of the film, which vary within 29–33.5 and 46–48 GPa, respectively.

Synthesis and magnetic characterization of CoMoN2 nanoparticles

A new ternary nitride, CoMoN2, was prepared in the nanosize regime of 9.0 ± 2.0 nm, by nitridation of the precursor intermetallic nitride Co3Mo3N. XRD–Rietveld analysis revealed the presence of 0.60 (±0.02) mass % of Co impurity phase. The calculated space groups of CoMoN2 and Co are P6 3 /mmc and Fm-3m, respectively. The N atoms lie at the interstitial sites and the 12 calculated nitrogen sites indicate the presence of a layered structure. The XPS studies indicated the presence of the nitride and surface oxynitride/oxide phases. CoMoN2 is an interstitial nitride with Co and Mo in the zero oxidation state. The room temperature susceptibility is estimated after subtracting the ferromagnetic contribution from cobalt and found to be 2.7 × 10−4 emu g−1 Oe−1, indicating the Pauli-paramagnetic nature. The ferromagnetic exchange interactions between the Co atoms in CoMoN2 are reduced due to the presence of Mo and N in the crystal lattice. The hysteresis loop shift 19 Oe is attributed to the demagnetizing dipolar fields created in the soft CoMoN2 phase by the hard Co phase.

Activated self-propagating high-temperature synthesis of aluminum and titanium nitrides

The paper addresses a possible route for the manufacturing of aluminum and titanium nitride powders by the self-propagating high-temperature synthesis (SHS) method. It was revealed, that a small amount of ammonium chloride NH 4Cl additive to the metal powder allows the production of aluminum and titanium nitride powders with a good yield even at a rather low pressure of nitrogen. The influence of NH 4Cl amount, metal particle size, porosity of the pressed sample, and nitrogen pressure on the extent of metal conversion into its nitride was experimentally studied. Synthesis of complex nitrides of intermetallics, based on titanium, aluminum and nickel, has also been investigated. Samples were produced by a direct SHS of nickel–aluminum and titanium–aluminum mixtures in a nitrogen atmosphere. Experimental results have shown that during nitridation of Ni–Al and Ti–Al mixtures, respectively, solid solutions of Ni, Al, N and Ti, Al, N correspondingly, are formed, containing mainly the simple nitrides (i.e. TiN and AlN phases), and only small amounts of the stoichiometric ternary complex intermetallic nitrides.

Self-propagating high-temperature synthesis of complex nitrides of intermetallics

In our previous papers, the Self-Propagating High-Temperature Synthesis (SHS) of aluminium and titanium nitrides was studied. In this paper the synthesis of the complex nitrides of intermetallics, based on titanium, aluminium and nickel, was carried out. The samples were produced by the direct SHS of nickel–aluminium and titanium–aluminium mixtures in a nitrogen atmosphere, as well as by the SHS synthesis of nickel–aluminium and titanium–aluminium intermetallics followed by pulsed plasma ion nitriding. Composition of products was studied by chemical analysis, as well as by X-ray diffraction and X-ray photoelectron spectroscopy. Experiments revealed that the highest extent of nitridation was achieved during direct one-stage SHS synthesis of the complex intermetallic nitrides.

The simultaneous powder X-ray and neutron diffraction refinement of two η-carbide type nitrides, Fe3Mo3N and Co3Mo3N, prepared by ammonolysis and by plasma nitridation of oxide precursors

Abstract The intermetallic nitrides Fe3Mo3N and Co3Mo3N were synthesized by the ammonolysis of the ternary oxide precursors FeMoO4 and CoMoO4 as well as by plasma nitridation of the oxide precursors. The structures of Fe3Mo3N and Co3Mo3N were determined from the simultaneous Rietveld refinements of powder X-ray and neutron diffraction data. Both compounds were found to be isostructural with η-Fe3W3C which crystallizes with cubic symmetry in the space group Fd 3 m with Z=16. The lattice parameters were found to be a=11.0859(3) A and a=11.0270(6) A for Fe3Mo3N and Co3Mo3N, respectively. The general atomic positions that gave the best refinement for the intermetallic nitrides M3Mo3N are Mo on 48f, M on 32e and 16d and N on 16c. The structure consists of corner shared NMo6 octahedra with the metal atoms occupying the sites between the octahedra. Magnetic susceptibility data for Co3Mo3N was found not to follow the Curie law.

ChemInform Abstract: Synthesis of Intermetallic Nitrides by Solid‐State Precursor Reduction.

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Synthesis of intermetallic nitrides by solid-state precursor reduction

Solid-state nitrides are of interest because they exhibit technologically useful properties. For example, some transition-metal nitrides are extremely hard and strong yet are good conductors of heat and electricity. Others show interesting catalytic properties, where the similarity metals has been pointed out. In this study, transition-mental molybdates FeMoO[sub 4] and NiMoO[sub 4] were used as precursors for ternary transition-metal nitrides. 42 refs., 4 figs., 3 tabs.

Synthesis of New Nitrides Using Solid State Oxide Precursors

AbstractSeveral novel transition metal nitrides were synthesized via ammonolysis of solid state oxide precursors at temperatures ranging from 700°C-900°C and reaction times ranging from 12 hours to 4 days. Both intermetallic nitrides, Fe3Mo3N and Co3Mo3N, and ionic/covalent nitrides, FeWN2, MnWN2, Ta5N6 and Nb5N6, were prepared by this method. The products were characterized by powder X-ray diffraction and their structures were determined by powder X-ray Rietveld refinement. The intermetallic nitrides were found to be isostructural with the eta-carbide structure, Fe3W3C, while the ionic/covalent nitrides have layered structures, with metals in octahedral and trigonal prismatic coordination environments. Two polymorphs of the MnWN2 composition, α-MnWN2 and β-MnWN2, were isolated after ammonolysis at 700°C and 800°C, respectively. While the alpha phase can be converted into the beta phase by heating to 800°C under ammonia, annealing the beta phase at 700°C did not result in a structural transformation. Magnetic measurements show that FeWN2 orders antiferromagnetically at 45K. The magnetic ordering temperature was confirmed by M6ssbauer spectroscopy. All the other nitrides were paramagnetic down to 5K. Conductivity measurements show that FeWN2 and MnWN2 are metallic.