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Using the first-principles calculational method based on the density functional theory, we study the structural instabilities, phonon softenings, and their relation to the superconductivities of two -pyrochlore oxide superconductors AOs2O6(A=K, Rb). It is found that there are structural instabilities of alkali ions along the 〈111〉 direction in the two -pyrochlore oxide superconductors AOs2O6(A=K, Rb), especially in KOs2O6. Meanwhile, a comparison of the phonon frequency at zone-center between KOs2O6 and RbOs2O6 shows that the frequency of KOs2O6 is lower in general than that of RbOs2O6, leading to the stronger electron-phonon coupling. We conclude that K atom located in a large oxygen cage has an unusual large atomic displacement parameter and strong activity, thereby resulting in strong phonon softening. This is the foundamental cause for stronger electron-phonon coupling and higher superconducting transition temperature of KOs2O6. These are of significance for explaining the superconductivities in -pyrochlore oxide superconductors AOs2O6(A=K, Rb).
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Keywords:
- -pyrochlore oxides superconductors /
- structural instability /
- phonon softening /
- superconductivity
[1] Yonezawa S, Muraoka Y, Matsushita Y, Hiroi Z 2004 J. Phys: Condens Matter 16 L9-L12
[2] Yonezawa S, Muraoka Y, Matsushita Y, Hiroi Z 2004 J. Phys. Soc. Jpn. 73 819
[3] [4] [5] Yamaura J, Yonezawa S, Muraoka Y Hiroi Z 2006 J. Solid State Chem. 179 336
[6] [7] Hiroi Z, Yonezawa S, Nagao Y, Yamaura J 2007 Phys. Rev. B 76 014523
[8] [9] Brhwiler M, Kazakov S M, Karpinski J, Batlogg B 2006 Phys. Rev. B 73 094518
[10] [11] Yoshida M, Arai K, Kaido R, Takigawa M, Yonezawa S, Muraoka Y, Hiroi Z 2007 Phys. Rev. Lett. 98 197002
[12] [13] Hasegawa T, Takasu Y, Ogita N, Udagawa M 2007 Phys. Rev. B 77 064303
[14] [15] Wang W, Sun J F, Liu M, Liu S 2009 Acta Phys. Sin. 58 5632 (in Chinese) [王玮, 孙家法, 刘楣, 刘甦 2009 58 5632]
[16] Xin X G, Chen X, Zhou J J, Shi S Q 2011 Acta Phys. Sin. 60 028201 (in Chinese) [忻晓桂, 陈香, 周晶晶, 施思齐 2011 60 028201]
[17] [18] [19] Blaha P, Schwarz K 2003 Comp. Mater. Sci. 28 259
[20] Wu Z, Cohen R E 2006 Phys. Rev. B 73 235116
[21] [22] [23] Baroni S, de Gironcoli S, Dal Corso A, Giannozzi P, Avalibale from http: //www.pwscf.org
[24] Vanderbilt D 1990 Phys. Rev. B 41 7892
[25] [26] [27] Perdew J P, Burke K, Ernzerhof M 1996 Phys. Rev. Lett. 77 3865
[28] Kendziora C A, Sergienko I A, Jin R, He J, Keppens V, Sales B C, Mandrus D 2005 Phys. Rev. Lett. 95 125503
[29] [30] Sergienko I A, Curnoe S H 2003 J. Phys. Soc. Jpn. 72 1607
[31] [32] [33] Yamaura J, Hiroi Z 2002 J. Phys. Soc. Jpn. 71 2598
[34] An J M, Pickett W E 2001 Phys. Rev. Lett. 86 4366
[35] [36] [37] Huang G Q, Chen L F, Liu M, Xing D Y 2004 Phys. Rev. B 69 064509
[38] Ma R, Huang G Q, Liu M 2007 Acta Phys. Sin. 56 4960 (in Chinese) [马荣, 黄桂芹, 刘楣 2007 56 4960]
[39] [40] Zhang J H, Ma R, Liu S, Liu M 2006 Acta Phys. Sin. 55 4816 (in Chinese) [张加宏, 马荣, 刘甦, 刘楣 2006 55 4816]
[41] [42] Ttnc H M, Srivastava G P 2006 J. Phys: Condens Matter 18 11089
[43] [44] Li B, Xing Z W, Liu M 2011 Acta Phys. Sin. 60 077402 (in Chinese) [李斌, 邢钟文, 刘楣 2011 60 077402]
[45] [46] Wang W, Sun J F, Li S W, Lu H Y 2012 Physica C 472 29
[47] -
[1] Yonezawa S, Muraoka Y, Matsushita Y, Hiroi Z 2004 J. Phys: Condens Matter 16 L9-L12
[2] Yonezawa S, Muraoka Y, Matsushita Y, Hiroi Z 2004 J. Phys. Soc. Jpn. 73 819
[3] [4] [5] Yamaura J, Yonezawa S, Muraoka Y Hiroi Z 2006 J. Solid State Chem. 179 336
[6] [7] Hiroi Z, Yonezawa S, Nagao Y, Yamaura J 2007 Phys. Rev. B 76 014523
[8] [9] Brhwiler M, Kazakov S M, Karpinski J, Batlogg B 2006 Phys. Rev. B 73 094518
[10] [11] Yoshida M, Arai K, Kaido R, Takigawa M, Yonezawa S, Muraoka Y, Hiroi Z 2007 Phys. Rev. Lett. 98 197002
[12] [13] Hasegawa T, Takasu Y, Ogita N, Udagawa M 2007 Phys. Rev. B 77 064303
[14] [15] Wang W, Sun J F, Liu M, Liu S 2009 Acta Phys. Sin. 58 5632 (in Chinese) [王玮, 孙家法, 刘楣, 刘甦 2009 58 5632]
[16] Xin X G, Chen X, Zhou J J, Shi S Q 2011 Acta Phys. Sin. 60 028201 (in Chinese) [忻晓桂, 陈香, 周晶晶, 施思齐 2011 60 028201]
[17] [18] [19] Blaha P, Schwarz K 2003 Comp. Mater. Sci. 28 259
[20] Wu Z, Cohen R E 2006 Phys. Rev. B 73 235116
[21] [22] [23] Baroni S, de Gironcoli S, Dal Corso A, Giannozzi P, Avalibale from http: //www.pwscf.org
[24] Vanderbilt D 1990 Phys. Rev. B 41 7892
[25] [26] [27] Perdew J P, Burke K, Ernzerhof M 1996 Phys. Rev. Lett. 77 3865
[28] Kendziora C A, Sergienko I A, Jin R, He J, Keppens V, Sales B C, Mandrus D 2005 Phys. Rev. Lett. 95 125503
[29] [30] Sergienko I A, Curnoe S H 2003 J. Phys. Soc. Jpn. 72 1607
[31] [32] [33] Yamaura J, Hiroi Z 2002 J. Phys. Soc. Jpn. 71 2598
[34] An J M, Pickett W E 2001 Phys. Rev. Lett. 86 4366
[35] [36] [37] Huang G Q, Chen L F, Liu M, Xing D Y 2004 Phys. Rev. B 69 064509
[38] Ma R, Huang G Q, Liu M 2007 Acta Phys. Sin. 56 4960 (in Chinese) [马荣, 黄桂芹, 刘楣 2007 56 4960]
[39] [40] Zhang J H, Ma R, Liu S, Liu M 2006 Acta Phys. Sin. 55 4816 (in Chinese) [张加宏, 马荣, 刘甦, 刘楣 2006 55 4816]
[41] [42] Ttnc H M, Srivastava G P 2006 J. Phys: Condens Matter 18 11089
[43] [44] Li B, Xing Z W, Liu M 2011 Acta Phys. Sin. 60 077402 (in Chinese) [李斌, 邢钟文, 刘楣 2011 60 077402]
[45] [46] Wang W, Sun J F, Li S W, Lu H Y 2012 Physica C 472 29
[47]
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