Ab initio study of the stable phases of 1:1 tantalum nitride

Grumski, Michael; Dholabhai, Pratik P.; Adams, James B.

doi:10.1016/j.actamat.2013.03.018

Cited by 33 publications

(28 citation statements)

References 30 publications

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“…2 and 4 While the B h and ε phases exhibit a considerable increase in E f for increasing y values at low aluminium fractions x (i.e., metal vacancies are undesirable structural perturbation, a defect in the very sense of the term), the formation energy of B1 becomes more negative with increasing y, making the structure more stable. This is in agreement with calculations by other authors of pure TaN, which showed that the cubic phase favours vacancies [36,41,49]. The decrease in E f extends up to x ≈ 0.5 where the metal vacancies eventually have an adverse effect.…”

Section: Origin Of the Extended Stability Range Of The Cubic Phasesupporting

confidence: 92%

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Vacancy-driven extended stability of cubic metastable Ta-Al-N and Nb-Al-N phases

Pacher

Mayrhofer

Holec

2017

Surface and Coatings Technology

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Quantum mechanical calculations had been previously applied to predict phase stability in many ternary and multinary nitride systems. While the predictions were very accurate for the Ti-Al-N system, some discrepancies between theory and experiment were obtained in the case of other systems. Namely, in the case of Ta-Al-N, the calculations tend to overestimate the minimum Al content necessary to obtain a metastable solid solution with a cubic structure. In this work, we present a comprehensive study of the impact of vacancies on the phase fields in quasi-binary TaN-AlN and NbN-AlN systems. Our calculations clearly show that presence of point defects strongly enlarges the cubic phase field in the TaN-AlN system, while the effect is less pronounced in the NbN-AlN case. The present phase stability predictions agree better with experimental observations of physical vapour deposited thin films reported in the literature than that based on perfect, non-defected structures. This study shows that a representative structural model is crucial for a meaningful comparison with experimental data.

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Section: Origin Of the Extended Stability Range Of The Cubic Phasesupporting

confidence: 92%

“…The ground state of TaN is a hexagonal ε-phase (sometimes also denoted as π-phase, space group #189, Fig. 1e) [36]. A hexagonal B h -phase (sometimes also denoted as θ-phase, space group #187) is a metastable polymorph of TaN with energy of formation being ≈ 36 meV/at.…”

Section: Introductionmentioning

confidence: 99%

Vacancy-driven extended stability of cubic metastable Ta-Al-N and Nb-Al-N phases

Pacher

Mayrhofer

Holec

2017

Surface and Coatings Technology

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“…However, the cubic phase is expected to be stabilized by atomic vibration at higher temperatures, rendering it more stable than the WC-type phase. It is therefore more relevant to consider it as a competing phase here [28,29].…”

Section: Computational Detailsmentioning

confidence: 99%

Thermodynamic Stability, Thermoelectric, Elastic and Electronic Structure Properties of ScMN2-Type (M = V, Nb, Ta) Phases Studied by ab initio Calculations

et al. 2019

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ScMN2-type (M = V, Nb, Ta) phases are layered materials that have been experimentally reported for M = Ta and Nb, but they have up to now not been much studied. However, based on the properties of binary ScN and its alloys, it is reasonable to expect these phases to be of relevance in a range of applications, including thermoelectrics. Here, we have used first-principles calculations to study their thermodynamic stability, elastic, thermoelectric and electronic properties. We have used density functional theory to calculate lattice parameters, the mixing enthalpy of formation and electronic density of states as well as the thermoelectric properties and elastic constants (cij), bulk (B), shear (G) and Young’s (E) modulus, which were compared with available experimental data. Our results indicate that the considered systems are thermodynamically and elastically stable and that all are semiconductors with small band gaps. All three materials display anisotropic thermoelectric properties and indicate the possibility to tune these properties by doping. In particular, ScVN2, featuring the largest band gap exhibits a particularly large and strongly doping-sensitive Seebeck coefficient.

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“…Ta-C, Hf-C, Zr-C), which crystallize in the face centered cubic (fcc) NaCl (Fm m, #225) structure, Ta-N crystalizes predominantly in hexagonal (hex) structure types. Two highly similar prototypes, ε-TaN (P6/mmm, #191) and π-TaN (P 2m, #189) are known for Ta-N, with π-TaN being the most stable one 19 . In an equilibrium state, π-TaN transforms to fcc δ-TaN (Fm m, #225) above 1950 °C 20 , highlighting that fcc structured TaN can be accessed through higher entropy (e.g.…”

Section: Introductionmentioning

confidence: 99%

Tuning structure and mechanical properties of Ta-C coatings by N-alloying and vacancy population

Glechner

Mayrhofer

Holec

et al. 2018

Sci Rep

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Tailoring mechanical properties of transition metal carbides by substituting carbon with nitrogen atoms is a highly interesting approach, as thereby the bonding state changes towards a more metallic like character and thus ductility can be increased. Based on ab initio calculations we could prove experimentally, that up to a nitrogen content of about 68% on the non-metallic sublattice, Ta-C-N crystals prevail a face centered cubic structure for sputter deposited thin films. The cubic structure is partly stabilized by non-metallic as well as Ta vacancies – the latter are decisive for nitrogen rich compositions. With increasing nitrogen content, the originally super-hard fcc-TaC0.71 thin films soften from 40 GPa to 26 GPa for TaC0.33N0.67, accompanied by a decrease of the indentation modulus. With increasing nitrogen on the non-metallic sublattice (hence, decreasing C) the damage tolerance of Ta-C based coatings increases, when characterized after the Pugh and Pettifor criteria. Consequently, varying the non-metallic sublattice population allows for an effective tuning and designing of intrinsic coating properties.

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Ab initio study of the stable phases of 1:1 tantalum nitride

Cited by 33 publications

References 30 publications

Vacancy-driven extended stability of cubic metastable Ta-Al-N and Nb-Al-N phases

Vacancy-driven extended stability of cubic metastable Ta-Al-N and Nb-Al-N phases

Thermodynamic Stability, Thermoelectric, Elastic and Electronic Structure Properties of ScMN2-Type (M = V, Nb, Ta) Phases Studied by ab initio Calculations

Tuning structure and mechanical properties of Ta-C coatings by N-alloying and vacancy population

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