Neutron powder diffraction studies of transition metal hemicarbides M2C1−—II. In situ high temperature study on W2C1− and Mo2C1−

Épicier, Thierry; Dubois, J.; Esnouf, C.; Fantozzi, G.; Convert, P.

doi:10.1016/0001-6160(88)90293-3

Cited by 141 publications

(101 citation statements)

References 14 publications

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“…The relative stabilities of different carbon positions within the interstitial sites was also investigated. The results confirm the experimentally observed Fe 2 N-ζ structure [59] as the most stable. The bulk modulus and formation energy of Mo 2 C was also evaluated.…”

Section: Resultssupporting

confidence: 90%

“…The bulk lattice constants were determined to be a=4.839 A, b=6.173Å, and c=5.322Å which are within 2.5% of the experimental values (a=4.72, b=6.01, c=5.20) [59]. The relative stabilities of different carbon positions within the interstitial sites was also investigated.…”

Section: Resultsmentioning

confidence: 71%

“…Orthorhombic Mo 2 C 3.1.1. Bulk structure Molybdenum carbide exists in three stable phases at temperatures below 1500 K: orthorhombic Mo 2 C at low temperatures, and hexagonal Mo 2 C or MoC at higher temperatures [59]. This study focuses on the orthorhombic Mo 2 C crystal structure, henceforth abbreviated as simply Mo 2 C. The orthorhombic structure consists of Mo atoms distorted slightly from hexagonal positions with carbons inserted into the interstitial sites as shown in Figure 1(a).…”

Section: Resultsmentioning

confidence: 99%

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Elementary steps of syngas reactions on Mo2C(001): Adsorption thermochemistry and bond dissociation

Medford

Vojvodić

Studt

et al. 2012

Journal of Catalysis

103

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Density functional theory (DFT) and ab initio thermodynamics are applied in order to investigate the most stable surface and subsurface terminations of Mo 2 C(001) as a function of chemical potential and in the presence of syngas. The Mo-terminated (001) surface is then used as a model surface to evaluate the thermochemistry and energetic barriers for key elementary steps in syngas reactions. Adsorbtion energy scaling relations and Brønsted-Evans-Polanyi relationships are established and used to place Mo 2 C into the context of transition metal surfaces. The results indicate that the surface termination is a complex function of reaction conditions and kinetics. It is predicted that the surface will be covered by either C 2 H 2 or O depending on conditions. Comparisons to transition metals indicate that the Mo-terminated Mo 2 C(001) surface exhibits carbon reactivity similar to transition metals such as Ru and Ir, but is significantly more reactive towards oxygen.

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Section: Resultssupporting

confidence: 90%

Section: Resultsmentioning

confidence: 71%

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Elementary steps of syngas reactions on Mo2C(001): Adsorption thermochemistry and bond dissociation

Medford

Vojvodić

Studt

et al. 2012

Journal of Catalysis

103

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“…Re 2 N and Re 2 C having space group P63/mmc (194) [8,10] can only be stable at high temperature-high pressure condition. Both Cr 2 N and beta-Ta 2 N [12,13] show space group of P63/mmc (194) at ambient condition and Fe 2 N and Mo 2 C shows stability in the space group of Pbcn (60) at ambient condition while they are showing p3 − m1(164) symmetry only at high temperature [14]. None of them crystallizes in a space group of P 3 − m1 (164) at ambient condition which opens up to explore the hydrostatic quenching process more extensively.…”

Section: Introductionmentioning

confidence: 99%

Stabilizing a hexagonal Ru2C via Lifshitz transition under pressure

Sun

Chakraborty

Ahuja

2013

Applied Physics Letters

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A new type of heavy transition metal carbide (TMC), Ru 2 C with a space group of p3 − m1 (164) was synthesized experimentally at high pressurehigh temperature [J Phys. Condens. Matter. 2012 Sep 12; 24(36): 362202.] and it was consequently quenched to ambient condition. We have carried out the dynamical stability study, which reveals the instability at ambient condition. The effect of pressure has been taken into consideration in order to stabilize as the reported synthesizing condition. We have found that it can be stabilized from 30 GPa to 110 GPa. The stronger 4d -2p hybridization and the formation of a cage like Fermi surface do impact the stability and also illustrates a Lifshitz transition. We have also found a mixed 4d-2p bands crossing the Fermi level form a Fermi surface piece at Γ point under pressure. The freshly appearing bands provide a tunnel for quantum transportation and it reduces the density of states at Fermi level, which further stabilizes the lattice under pressure.

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“…The sequence of the change in the polymorphic modifications of the carbide W 2 C as a function of temperature that is assumed in handbook [1] is different from that proposed in [3]. Table 1 lists the phases and the characteristics according to the data in [1, 3,[6][7][8][9][10][11][12][13][14]. In [1], the following modifications are indicated for the carbide W 2 C: ordered rhombic phase of type PbO 2 (ξ-Fe 2 N) above 2500°C, disordered hexagonal phase of type L′ 3 within the range 2100°C to 2500°C, and ordered phase of type C6 at 1250-2100°C.…”

Section: Introductionmentioning

confidence: 99%

Ordering in the carbide W2C and phase equilibria in the tungsten ? carbon system in the region of its existence

Kublii

Velikanova

2004

Powder Metall Met Ceram

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We have studied alloys in the W − C system with compositions 24 to 48 at.% C, melted in an arc furnace, homogenized and quenched from temperatures of 1450°C to 2650°C or cooled stepwise from a subsolidus temperature down to 850°C, and annealed for a prolonged period at this temperature or at temperatures close to it. We studied the specimens by x-ray single-crystal and powder diffraction, metallography, and differential thermal analysis. We have shown that the carbide W 2 C exists in two modifications: an hexagonal phase with structure of type L′ 3 crystallizes from the melt, which at T ≈ 1850°C transforms to an ordered hexagonal phase of the ε-Fe 2 N type. The latter, for a carbon content of about 32 at.% and T ≈ 1250°C, also decomposes according to a eutectoid reaction to and WC. This decomposition is accompanied by formation of a metastable phase of the ξ-Fe 2 N type as an intermediate. Taking the results obtained and literature data into consideration, we have corrected the phase diagram for the W − C system.

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Neutron powder diffraction studies of transition metal hemicarbides M2C1−—II. In situ high temperature study on W2C1− and Mo2C1−

Cited by 141 publications

References 14 publications

Elementary steps of syngas reactions on Mo2C(001): Adsorption thermochemistry and bond dissociation

Elementary steps of syngas reactions on Mo2C(001): Adsorption thermochemistry and bond dissociation

Stabilizing a hexagonal Ru2C via Lifshitz transition under pressure

Ordering in the carbide W2C and phase equilibria in the tungsten ? carbon system in the region of its existence

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