Preparation of binary single-phase line compounds via diffusion couples: The subnitride phases η-Hf3N2−x and ζ-Hf4N3−x

Lengauer, W.; Rafaja, David; Täubler, R.; Kral, C.; Ettmayer, Peter

doi:10.1016/0956-7151(93)90230-p

Cited by 41 publications

(18 citation statements)

References 17 publications

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“…The fact that the Ta 3 C 2 compound lies on the convex hull suggests that the zeta phase can be regarded as having a clear defined stoichiometry like α‐Ta 2 C. This further suggests the need to rename zeta phase from ζ‐Ta 4 C 3‐x to ζ‐Ta 3 C 2 , as Ta 3 C 2 is stable, has the correct experimentally reported metal stacking sequence, and the ζ‐Ta 4 C 3 resides off the convex hull and thus is metastable. It is worth noting that phases of composition M 3 X 2‐x are reported in the Hf‐N and Ti‐N systems, are called the eta phase, which are distinct from the zeta phase reported here. Specifically, the eta phase has a (hhc) 3 metal stacking sequence, or 9R, instead of the (hhcc) 3 of the zeta phase further establishing the ζ‐Ta 3 C 2 as a unique phase.…”

Section: Resultsmentioning

confidence: 47%

A computational search for the zeta phase in the tantalum carbides

Weinberger

Thompson

2018

J Am Ceram Soc

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A systematic electronic structure density functional theory search for the zeta phase in the tantalum carbon system has been conducted, demonstrating that the zeta phase does indeed lie on the convex hull, establishing low‐temperature thermodynamic stability, and is structurally stable. Even though the zeta phase is most oft reported as a R3¯m ζ‐Ta4C3‐x structure, these new computational results reveal that the perfectly ordered zeta phase occurs at the Ta3C2 composition and belongs to the C2/m space group. Furthermore, these results suggest that the R3¯m space group may be a result of an order‐disorder transition and potential deviations from ideal stoichiometry at higher temperatures. The structure of this Ta3C2 compound can be described as ordered strings of carbon vacancies on a single carbon plane, which is also the preferred plane where additional carbon vacancies or interstitials form. These defects have modest formation energies, which provides further explanation for the small homogeneity range in zeta phase.

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Section: Resultsmentioning

confidence: 47%

A computational search for the zeta phase in the tantalum carbides

Weinberger

Thompson

2018

J Am Ceram Soc

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“…This was performed by a computer program [11] that takes into account the dependency of layer thickness as a function of sample thickness. The influence was shown recently [12] on plane-sheet and wedge-type samples to be of crucial importance already in samples of several millimeter thick- ness. In plane-sheet samples, the layers are thicker than in corresponding samples of semi-infinite diffusion geometry (thick samples).…”

Section: B Nitride Layer Growthmentioning

confidence: 96%

Reaction diffusion and phase equilibria in the V-N system

Teichmann

Lengauer

Ettmayer

et al. 1997

Metall Mater Trans A

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The formation of phase bands in in situ diffusion couples of the V-N system was studied by the reaction of vanadium sheet with pure nitrogen within the temperature range 1100 ЊC to 1700 ЊC and the nitrogen pressure range 2 to 24 bar. Under these conditions, phase bands of ␤-V 2 N and ␦-VN 1Ϫx develop. The morphology of the ␤-V 2 N/␣-V(N) interface depends on the saturation state of the ␣-V(N) core. If the nitrogen content in ␣-V(N) is high, the interface has a jagged appearance, whereas at low nitrogen contents of the ␣-V(N) phase, the interface is planar. Electron probe microanalysis (EPMA) was used to measure the diffusion profiles within the couples. The homogeneity regions of the nitride phases were established and the phase diagram accordingly corrected. From the growth rates of the phase bands, the mean composition-independent nitrogen diffusivities in ␤-V 2 N and ␦-VN 1Ϫx were derived. These diffusivities follow an Arrhenius equation with activation energies of 2.92 (␤-V 2 N) and 2.93 eV (␦-VN 1Ϫx ). By using ␦-VN 1Ϫx as a starting material and a low nitrogen pressure during annealing, it could be shown that the direction of nitrogen diffusion can be reversed, i.e., ␤-V 2 N is formed on the surface of the couple as a result of out-diffusion of nitrogen.

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“…In addition to various diffusion studies of interstitial oxygen and nitrogen in these metals and alloys [2][3][4][5][6][7][8], many works are related to the self-diffusion and the impurity diffusion in these materials, as well in ␣-Ti [9][10][11][12][13][14][15], ␣-Zr [16][17][18][19][20][21], ␣-Hf [22,23] phases as in ␤-Ti [24][25][26][27][28], ␤-Zr [29][30][31][32] or ␤-Hf [33] phases. A summary of the results former to 1966 was published in the work of Adda and Philibert [34].…”

Section: Introductionmentioning

confidence: 99%