Structure and phase composition of Nb-C deposited films

Володин, В. Н.; Teleushev, Yu. Zh.; Жаканбаев, Е. А.

doi:10.1134/s0031918x13020130

Cited by 10 publications

(4 citation statements)

References 7 publications

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“…Although the configurations of carbon near niobium lattice defects are favorable compared to interstitial carbon far away from lattice defects, Nb 2 C has the lowest energy so will preferentially form under favorable kinetic conditions. Nb 2 C has been formed in sputter-deposited thin films with compositions as low as 1.9% C. 19 Carbon has been shown to migrate to dislocations and replace oxygen in that region during strain aging experiments at 155 °C, 32 which may convert to carbide phases once a sufficient local concentration has been reached. Additional ordered phases that are not included in this study are present in experimental phase diagram, 18 and others have been predicted by first-principles calculations 58 as well.…”

Section: Niobium Vacancy Dimer and Trimer Configurations And Their In...mentioning

confidence: 99%

“…Although interstitial carbon in niobium has some similar properties to interstitial oxygen and nitrogen, it has not been studied as intensively, perhaps because it has a much lower solubility. , The lack of attention paid to carbon in niobium may be an important oversight, however. Recent secondary ion mass spectroscopy measurements of SRF niobium samples indicate local carbon concentrations of 10 –1 to 10 –2 at % depending on the specimen history and heat treatment, and recent Raman spectroscopy studies indicate that large amounts of carbon are present in various forms as local clusters on niobium cavity and sample surfaces .…”

Section: Introductionmentioning

confidence: 99%

“…17 Although interstitial carbon in niobium has some similar properties to interstitial oxygen and nitrogen, 13 it has not been studied as intensively, perhaps because it has a much lower solubility. 18,19 The lack of attention paid to carbon in niobium may be an important oversight, however. Recent secondary ion 20 How the carbon collects is not known; the previously described reports emphasize clean handling and rule out casual environmental contributions.…”

Section: Introductionmentioning

confidence: 99%

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First-Principles Study of Carbon and Vacancy Structures in Niobium

2015

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The interstitial chemical impurities hydrogen, oxygen, nitrogen, and carbon are important for niobium metal production and particularly for the optimization of niobium SRF technology. These atoms are present in refined sheets and can be absorbed into niobium during processing treatments, resulting in changes to the residual resistance and the performance of SRF cavities. A first-principles approach is taken to study the properties of carbon in niobium, and the results are compared and contrasted with the properties of the other interstitial impurities. The results indicate that C will likely form precipitates or atmospheres around defects rather than strongly bound complexes with other impurities. On the basis of the analysis of carbon and hydrogen near niobium lattice vacancies and small vacancy chains and clusters, the formation of extended carbon chains and hydrocarbons is not likely to occur. Association of carbon with hydrogen atoms can, however, occur through the strain fields created by interstitial binding of the impurity atoms. Calculated electronic densities of states indicate that interstitial C may have a similar effect as interstitial O on the superconducting transition temperature of Nb.

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Section: Niobium Vacancy Dimer and Trimer Configurations And Their In...mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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First-Principles Study of Carbon and Vacancy Structures in Niobium

2015

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“…[12] Volodin et al explored the structures and phase compositions of Nb-C deposited films using the methods of ion-plasma sputtering and the co-precipitation of ultradispersed Nb and C particles. [13] Khvan et al described the thermodynamic assessment of Cr-Nb-C and Mn-Nb-C systems. [14] However, the stability and mechanical properties of Nb x C y compounds have not been systematically analyzed, and lacked theoretical research.…”

Section: Introductionmentioning

confidence: 99%

Stability and elastic properties of Nb _x C _y compounds

Gao¹,

Jiang²,

Liu³

et al. 2014

Chinese Phys. B

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Density functional theory (DFT) is applied to investigate the stability and mechanical properties of Nb x C y compounds. The structures of Nb x C y compounds are optimized, and the results are in good agreement with previous work. The calculated results of the cohesive energy and the formation enthalpy of Nb x C y show that they are thermodynamically stable structures, except for Pmc21-Nb 2 C. The mechanical properties such as the bulk modulus, Young's modulus, the shear modulus, and Poisson's ratio are obtained by Voigt-Reuss-Hill approximation. The results show that the Young's modulus and shear modulus of NbC are larger than other Nb x C y compounds. The mechanical anisotropy is characterized by calculating several different anisotropic indexes and factors, such as universal anisotropic index (A U ), shear anisotropic factors (A 1 , A 2 , A 3 ), and percent anisotropy (A B and A G ). The surface constructions of bulk and Young's moduli are illustrated to indicate the mechanical anisotropy. The hardness of Nb x C y compounds is also discussed in this paper. The estimated hardness for all Nb x C y compounds is less than 20 GPa.

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