Vacancy-cluster mechanism of metal-atom diffusion in substoichiometric carbides

Razumovskiy, Vsevolod I.; Ruban, Andrei V.; Odqvist, Joakim; Korzhavyi, Pavel A.

doi:10.1103/physrevb.87.054203

Cited by 35 publications

(36 citation statements)

References 40 publications

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“…Antisite defects were found to be quite unstable, suggesting chemical disorder will be low in ZrC. Razumovskiy et al [15] studied the migration of Zr via a vacancy-mediated mechanism in TiC and ZrC. For ZrC they found that the V Zr -6V C cluster was more stable than the isolated V Zr and that this species migrated with a barrier of 7.46 eV, the same value obtained from experiment [16].…”

Section: Introductionmentioning

confidence: 67%

Defect kinetics and resistance to amorphization in zirconium carbide

Zheng

Szlufarska

Morgan

2015

Journal of Nuclear Materials

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To better understand the radiation response of zirconium carbide (ZrC), and in particular its excellent resistance to amorphization, we have used density functional theory methods to study the kinetics of point defects in ZrC. The migration barriers and recombination barriers of the simple point defects are calculated using the ab initio molecular dynamics simulation and the nudged elastic band method. These barriers are used to estimate C and Zr interstitial and vacancy diffusion and Frenkel pair recombination rates. A significant barrier for C Frenkel pair recombination is found but it is shown that a large concentration of C vacancies reduces this barrier dramatically, allowing facile healing of radiation damage. The mechanisms underlying high resistance to amorphization of ZrC were analyzed from the perspectives of structural, thermodynamic, chemical and kinetic properties. This study provides insights into the amorphization resistance of ZrC as well as a foundation for understanding general radiation damage in this material.

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Section: Introductionmentioning

confidence: 67%

Defect kinetics and resistance to amorphization in zirconium carbide

Zheng

Szlufarska

Morgan

2015

Journal of Nuclear Materials

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“…As discussed in the following, introduction of carbon vacancy leads to the relaxation of carbon‐vacant Nb 6 C octahedrons and the strengthening of one thirds Nb3–C2 around the vacancy. The carbon vacancies prefer to occupy the 3NN sites rather than the 1NN or 2NN sites (1NN and 2NN stand for the first‐ and second‐nearest‐neighboring, respectively) to maximize the bond strengthening effect and lower the energy . As a result, the carbon vacancies in Nb 12 Al 3 C 8 form OETCVNs parallel to (0001) in the central carbon layer (Figure C), and the translation vector of the OETCVNs is 1/2[0001] of Nb 12 Al 3 C 8 unit cell (Figure D).…”

Section: Resultsmentioning

confidence: 99%

“…The carbon vacancies prefer to occupy the 3NN sites rather than the 1NN or 2NN sites (1NN and 2NN stand for the firstand second-nearestneighboring, respectively) to maximize the bond strengthening effect 40 and lower the energy. [17][18][19] As a result, the carbon vacancies in Nb 12 Al 3 C 8 form OETCVNs parallel to (0001) in the central carbon layer ( Figure 1C), and the translation vector of the OETCVNs is 1/2[0001] of Nb 12 Al 3 C 8 unit cell ( Figure 1D). These features also apply for another experimentally identified ordered phase, V 12 Al 3 C 8 .…”

Section: Methodsmentioning

confidence: 99%

“…8,16 According to the stateof-the-art first-principles calculations in Ref. [17][18][19] forming the third-nearest-neighboring (3NN) carbon vacancy triplets benefits to lower the energy and helps to stabilize the defective structure, which is credited to the redistribution of valence electrons around the carbon vacancies. In this work, changes in electronic structures and bonding features caused by OETCVNs are elucidated for the first time.…”

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confidence: 99%

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Influence of ordered carbon‐vacancy networks on the electronic structures and elastic properties of Nb₄AlC_3−x

Zhang

et al. 2016

J Am Ceram Soc.

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Carbon‐vacancy‐bearing Nb4AlC3−x has the best high‐temperature mechanical robustness among MAX phases. The existing form of the vacancies has been long overlooked. Recently, the vacancies in Nb4AlC3−x have been identified to be ordered, establishing an ordered compound Nb12Al3C8. Here, the spatial distribution of the ordered vacancies and their influences on bonding characteristics and elastic properties are unraveled by thoroughly comparing Nb12Al3C8 and vacancy‐free Nb4AlC3. In Nb12Al3C8, the carbon vacancies break only relatively weak Nb–C bonds and form ordered equilateral triangular carbon‐vacancy networks (OETCVNs) to maximize the bond strengthening effect. The networks slightly shift partial and total density of states toward the Fermi energy level, and bring about a feature of “de‐metallization”. Meanwhile, the presence of OETCVNs results in the softening of elastic modulus, decreasing of the anisotropy of Young's modulus, yet increasing that of shear modulus. These results shed lights on the carbon‐vacancy ordering behavior of MAX phases, and provide an opportunity to tailor their electronic structures and elastic properties through defect engineering.

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“…Thus in this case radiation is not the driving force for defect migration, but rather it allows interstitial loops to undergo thermal diffusion that would occur in the absence of trapping solutes. The situation is qualitatively different when it comes to ceramics where it is generally accepted that clusters of self-interstitials or vacancies are immobile at room temperature due to their high inherent migration barriers (typically between 4 and 7 eV [8,9,18]). Therefore, the observed diffusion of clusters in SiC is an athermal process induced by radiation, rather than triggered by radiation.…”

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confidence: 99%

Radiation-induced mobility of small defect clusters in covalent materials

Jiang¹,

He²,

Morgan³

et al. 2016

Phys. Rev. B

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Although defect clusters are detrimental to electronic and mechanical properties of semiconductor materials, annihilation of such clusters is limited by their lack of thermal mobility due to high migration barriers. Here, we find that small clusters in bulk SiC (a covalent material of importance for both electronic and nuclear applications) can become mobile at room temperature under the influence of electron radiation. So far, direct observation of radiationinduced diffusion of defect clusters in bulk materials has not been demonstrated yet. This finding was made possible by low angle annular dark field (LAADF) scanning transmission electron microscopy (STEM) combined with non-rigid registration technique to remove sample instability, which enables atomic resolution imaging of small migrating defect clusters. We show that the underlying mechanism of this athermal diffusion is ballistic collision between incoming electrons and cluster atoms. Our findings suggest that defect clusters may be mobile under certain irradiation conditions, changing current understanding of cluster annealing process in irradiated covalent materials. Main textDefect clusters can form in covalent materials during ion implantation (e.g., in semiconductor applications) [1,2] or during irradiation (e.g., in nuclear reactor applications) [3][4][5][6]. Accumulation of such clusters is highly detrimental to electronic, optical, and mechanical properties of these materials [1,4,7]. While point defects can often be eradicated by mutual recombination or diffusion to defect sinks, clusters of defects in covalent materials are known to be immobile and resist annealing because of their high energy barriers to migration [8,9]. For SiC specifically, accelerated molecular dynamics (MD) simulations have shown that the barrier to migration of clusters as small as just three C interstitials is ~4.3 eV [8], which means that these clusters are immobile below 1,200 K on typical experimental annealing time scales (i.e., 1 hour whereas the cluster performs less than 1 hop/day). Such high barriers explain why models of defect evolution in SiC have assumed clusters to be immobile even at elevated temperatures (e.g., Ref. [10,11]) and why the nature of such clusters, their resistance to high-temperature annealing, and their effects on opto-electronic properties have been a subject of many discussions in the semiconductor literature [12,13].In this letter, we report a direct observation of interstitial clusters diffusion in bulk SiC under the influence of electron radiation at room temperature. Although it is known that in metals

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Vacancy-cluster mechanism of metal-atom diffusion in substoichiometric carbides

Cited by 35 publications

References 40 publications

Defect kinetics and resistance to amorphization in zirconium carbide

Defect kinetics and resistance to amorphization in zirconium carbide

Influence of ordered carbon‐vacancy networks on the electronic structures and elastic properties of Nb₄AlC_3−x

Radiation-induced mobility of small defect clusters in covalent materials

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Vacancy-cluster mechanism of metal-atom diffusion in substoichiometric carbides

Cited by 35 publications

References 40 publications

Defect kinetics and resistance to amorphization in zirconium carbide

Defect kinetics and resistance to amorphization in zirconium carbide

Influence of ordered carbon‐vacancy networks on the electronic structures and elastic properties of Nb4AlC3−x

Radiation-induced mobility of small defect clusters in covalent materials

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Influence of ordered carbon‐vacancy networks on the electronic structures and elastic properties of Nb₄AlC_3−x