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MAX phases are potential future materials used in the nuclear industry. Recently, a new MAX phase Nb2GeC is predicted as the most stable compound, and confirmed by thin film synthesis.In the operation of fusion reactor, the accumulation and aggregation of helium and hydrogen produced from transmutation reactions would induce bubble formation and void swelling and further result in embrittlement and irradiation-induced hardening of the materials. High solubility and permeability of tritium and solubility of interstitial impurities like O, C, and N can also lead to embrittlement. In order to further investigate the characters of Nb2Ge in irradiation environment, ab initio calculations are performed on the energetics of O, H and He impurities in Nb2Ge. The study of all the impurities is carried out in two ways, substitutionally and interstitially. Formation energies due to substitution and interstitial are calculated, lattice parameters and unit cell volume of Nb2GeC with substitutional or interstitial impurities are obtained, and its electronic property is analysed by Mulliken population and electron charge density.The formation energies of H substitution are lower than those of O substitution and He substitution, hence H atoms are trapped more easily by some irradiation-induced vacancies. The formation energies of O subtitution indicate the sequence Ef(Osub-Nb)>Ef(Osub-Ge) ≈ Ef(Osub-C), which is related to the strength of bonds. Analysis on electron charge density and Mulliken population shows that C-O bond is stronger than Nb-O and Ge-O bond, and the bond lengths of C-O, Nb-O and Ge-O are 3.256, 2.118 and 1.985 Å respectively. Due to the interaction of O atom with Nb, Ge and C atoms in Nb2Ge, the O atom would deviate from the vacancy, and goes to the deformed sites in the crystal structure. As for H substitution, the formation energies of substitution show the sequence Ef(Hsub-Nb)>Ef(Hsub-Ge) > Ef(Hsub-C). C-H and Nb-H are ionic bond and covalent bond respectively, and their bond lengths are 3.131 and 2.706 Å respectively. The formation energies of He substitution present the sequence: Ef(Hesub-C) > Ef(Hesub-Nb) > Ef(Hesub-Ge), and suggest that the He atom is the easiest to be trapped by C vacancy. All O, H and He interstitials make lattice parameter a increase, c decrease and unit cell V shrink. Besides, the results of substitution and interstitial formation energies show that O, H and He impurities prefer to stay on octahedral sites. These results could provide initial physical picture for further understanding the accumulation and bubble formation of impurities in Nb2GeC.
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Keywords:
- MAX phase /
- first principles /
- impurity
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[23] Liu B, Wang J Y, Li F Z, Zhou Y C 2009 Appl. Phys. Lett. 94 181906
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[29] Oba F, Togo A, Tanaka I, Paier J, Kresse G 2008 Phys. Rev. B 77 245202
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[31] Sun X, Guo Y S, Wang X Q, Zhang Y 2012 Chin. J. Chem. Phys 25 261
[32] Zhang S B, Northrup J E 1991 Phys. Rev. Lett. 67 2339
[33] Lee S-G, Chang K J 1996 Phys. Rev. B 53 9784
[34] Baben M, Shang L, Emmerlich J, Schneider J M 2012 Acta. Mater. 60 4810
[35] Manzar A, Murtaza G, Khenata R, Masood Yousaf, Muhammad S, Hayatullah 2014 Chin. Phys. Lett. 31 067401
[36] Hou Q Y, Guo S Q, Zhao C W 2014 Acta Phys. Sin. 63 147101 (in Chinese) [侯清玉, 郭少强, 赵春旺 2014 物理学报 63 147101]
[37] Qiu P Y 2014 Chin. Phys. Lett. 31 066201
[38] Jia Y F, Shu X L, Xie Y, Chen Z Y 2014 Chin. Phys. B 23 076105
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[1] Zhang P B, Zhao J J, Qin Y, Wen Bin 2011 J. Nucl. Mater. 49 1
[2] Barabash V, Peacock A, Fabritsiev S, Kalinin G, Zinkle S, Rowcliffe A, Rensman J W, Tavassoli A A, Marmy P, Karditsas P J, Gillemot F, Akiba M 2007 J. Nucl. Mater. 21 367
[3] Yang X Y, Lu Y, Zhang P 2015 J. Nucl. Mater. 465 161
[4] Liu W G, Qian Y, Zhang D X, Liu W, Han H 2015 J. Nucl. Mater. 465 254
[5] Jiang S N, Wan F R, Long Y, Liu C X, Zhan Q, Somei O 2013 Acta Physica Sinica 62 166801 (in Chinese) [姜少宁, 万发荣, 龙毅, 刘传歆, 詹倩, 大貫惣明 2013 物理学报 62 166801]
[6] Gurovich B A, Kuleshova E A, Frolov A S, Maltsev D A, Prikhodko K E, Fedotova S V, Margolin B Z, Sorokin A A 2015 J. Nucl. Mater. 465 565
[7] Ehrlich K, Bloom E E, Kondo T 2000 J. Nucl. Mater. 79 283
[8] Kurtz R J, Abe K, Chernov V M, Kazakov V A, Lucas G E, Matsui H, Muroga T, Odette G R, Smith D L, Zinkle S J 2000 J. Nucl. Mater. 70 283
[9] Stoneham A M, Catlow R, Lidiard A B 2004 J. Phys.: Condens. Matter 16 S2597
[10] Weber W J, Wang L M 1996 N. Yu, Nucl. Instr. Meth. B 116 322
[11] Riley D P, Kisi E H 2007 J. Am. Ceram. Soc. 90 2231
[12] Nappé J C, Monnet I, Grosseau Ph, Audubert F, Guilhot B, Beauvy M, Benabdesselam M, Thomé L 2011 J. Nucl. Mater. 409 53
[13] Barsoum M W 2000 Prog. Solid State Chem 28 201
[14] Music D, Schneider J M 2007 JOM 59 60
[15] Eklund P, Beckers M, Jansson U, Högberg H, Hultman L 2010 Thin Solid Films 518 1851
[16] Barsoum M W, Radovic M 2011 Annu. Rev. Mater. Res. 41 195
[17] Wang J Y, Zhou Y C 2009 Annu. Rev. Mater. Res. 39 415
[18] Eklund P, Dahlqvist M, Tengstrand O, Hultman L, Lu J, Nedfors N, Jansson U, Ros é n J 2012 Phys. Rev. Lett. 109 035502
[19] Shein I R, Ivanovskii A L 2013 Physica B 410 42
[20] Ali M S, Parvin F, Islam A K M A, Hossain M A 2013 Comput. Mater. Sci. 74 119
[21] Chen J J, Duan J Z, Wang C L, Duan W S, Yang L 2014 Comput. Mater. Sci. 82 521
[22] Tan X Y, Wang J H, Zhu Y Y, Zuo A Y, Jin K X 2014 Acta Phys. Sin. 63 207301 (in Chinese) [谭兴毅, 王佳恒, 朱祎祎, 左安友, 金克新 2014 物理学报 63 207301]
[23] Liu B, Wang J Y, Li F Z, Zhou Y C 2009 Appl. Phys. Lett. 94 181906
[24] Segall M D, Lindan P L D, Probert M J, Pickard C J, Hasnip P J, Clark S J, Payne M C 2002 J. Phys.: Condens. Matter 14 2717
[25] Zhao S J, Xue J M, Wang Y G, Huang Q 2014 J. Appl. Phys. 115 023503
[26] Middleburgh S C, Lumpkin G R, Riley D 2013 J. Am. Ceram. Soc. 96 3196
[27] Zhao S J, Xue J M, Wang Y G, Huang Q 2014 J. Phys. Chem. Solids 75 384
[28] Xu Y G, Ou X D, Rong X M 2014 Mater. Lett. 116 322
[29] Oba F, Togo A, Tanaka I, Paier J, Kresse G 2008 Phys. Rev. B 77 245202
[30] Van de Walle C G, Neugebauer J 2004 J. Appl. Phys. 95 3851
[31] Sun X, Guo Y S, Wang X Q, Zhang Y 2012 Chin. J. Chem. Phys 25 261
[32] Zhang S B, Northrup J E 1991 Phys. Rev. Lett. 67 2339
[33] Lee S-G, Chang K J 1996 Phys. Rev. B 53 9784
[34] Baben M, Shang L, Emmerlich J, Schneider J M 2012 Acta. Mater. 60 4810
[35] Manzar A, Murtaza G, Khenata R, Masood Yousaf, Muhammad S, Hayatullah 2014 Chin. Phys. Lett. 31 067401
[36] Hou Q Y, Guo S Q, Zhao C W 2014 Acta Phys. Sin. 63 147101 (in Chinese) [侯清玉, 郭少强, 赵春旺 2014 物理学报 63 147101]
[37] Qiu P Y 2014 Chin. Phys. Lett. 31 066201
[38] Jia Y F, Shu X L, Xie Y, Chen Z Y 2014 Chin. Phys. B 23 076105
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