Effect of Pb substitution in bulk superconducting MgB2

Gu, Dawei; Cai, Yichen; Yau, J.K.F.; Yi, Chuixiang; Wu, T.; Yuan, Guoliang; Shen, Lin; X, Jin

doi:10.1016/s0921-4534(02)02186-x

Cited by 11 publications

(5 citation statements)

References 16 publications

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“…In all these dopings the axes parameters changed anisotropically. T C of MgB 2 shows a systematic decrease with the doping level in Mg 1−x M x B 2 for M = Sc [166][167][168], Co [169], Al, Li, Si, Zr, Cu [170], Nb, Mn, Fe, Sn, Co [171], Ni, Ag, Au [172], Ca [173], Ti, Y, Ho and Pb [162] and superconductivity is destroyed at higher doping levels for some of these dopants [172]. The dT C /dx is different for different substituents; it is high for magnetic substituents like Mn and Fe and is low for substituents like Mo and Ag [161].…”

Section: Doping Of Elementsmentioning

confidence: 96%

“…Of these studies Al substitution at the Mg site and C substitution at the B site are the most successful. Many of the other elements do not substitute (or the level of substitution is very low) into the lattice positions of either Mg or B [160,161], where the doping leads to the formation of finer secondary phase particles, causes significant disorders and distortions in the crystal lattice, which in turn reduce the T C [160][161][162]. Doping at the B site with materials like C, Be [163], F [164] or Cr [165] all resulted in a decrease in T C .…”

Section: Doping Of Elementsmentioning

confidence: 99%

See 1 more Smart Citation

Superconductivity of MgB₂in the BCS framework with emphasis on extrinsic effects on critical temperature

Vinod

Varghese

Syamaprasad³

2007

Supercond. Sci. Technol.

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The discovery of superconductivity in MgB2 with an unusually high TC of 39 K interested material scientists all over the world. Many of its superconducting properties, including an experimentally observed double energy gap, differ significantly with those of conventional LTS and HTS. Many scientists proposed exotic and unconventional mechanisms to explain the superconductivity in MgB2, but after more than 5 years it is now accepted that MgB2 is a BCS type superconductor with exceptionally high TC. In this review we discuss qualitatively the origin of superconductivity in MgB2 based on both experimental and theoretical results. The variation of TC of MgB2 with various processes, such as irradiation of high energy ions, doping and external pressure, etc., is discussed and reviewed. TC of MgB2 decreases upon irradiation, by applying external pressure and by most of the doping. The reduction of density of states at the Fermi level, increased band scattering and changes in the phonon frequencies are the main factors which reduce the TC under these conditions.

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Section: Doping Of Elementsmentioning

confidence: 96%

Section: Doping Of Elementsmentioning

confidence: 99%

Superconductivity of MgB₂in the BCS framework with emphasis on extrinsic effects on critical temperature

Vinod

Varghese

Syamaprasad³

2007

Supercond. Sci. Technol.

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“…However, T c of MgB 2 has not been enhanced in any substitutions/doping case. Nano SiC [13], Ti addition [14][15][16], C [17], ZrSi 2 and WSi 2 additions [18], Zn and Al double [19], Zr and Hf additions [20], Ir substitution [21], Pb substitution [22], Li and Na additions [23,24], Ag addition [25], Sn, Co and Fe addition [26], Ti, Zr, Mo, Mn, Fe, Ca, Al, Ag, Cu, Y, Ho additions [27,28] and Cr addition [29] were found to have a crucial role on the flux-pinning, critical current density and also irreversibility field of MgB 2 material. However, most of the substitutions/dopings have led to small or large decrease on T c or completely depression of superconductivity.…”

Section: Introductionmentioning

confidence: 99%

Co-addition into MgB2: The structural and electronic properties of (MgB2)2−xCox

Aksan

Yakıncı

Güldeste

2006

Journal of Alloys and Compounds

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“…49 In contrast with the other chemical doping effects, H atoms do not substitute into the lattice positions of either Mg or B, where the dopant atoms lead to the formation of secondary phase particles and cause significant anharmonicity and distortion in the crystal lattice, which in turn reduce the T c . 54 MgB 2 H x keeps the shape of the Fermi surface and the N͑E f ͒ with the absence of band filling. Furthermore, it shows strong electron-phonon coupling related to the increased frequency and linewidth of the E 2g mode.…”

mentioning

confidence: 99%

Raman study of element doping effects on the superconductivity ofMgB2

Chen

et al. 2008

Phys. Rev. B

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The influences of phonon frequency and unit cell volume on the superconductivity of element-doped MgB 2 are discussed with reference to a Raman study on SiC, C, Mn, and Al-Ag-doped Mg-B materials. A phenomenon has been found in the doped samples, in that the phonon frequency changes to counteract the crystal lattice variation to keep the system stable within a Grüneisen parameter of 2.0-4.0. The chemical doping effects on phonon frequency and unit cell volume can be explained by the harmonicity-anharmonicity competition in the compounds. A decreased electronic density of states is responsible for the depression of superconductivity that is seen in doped MgB 2 . The possibility of a high critical temperature, T c , in the Mg-B system exists if the material can possess both a high phonon frequency and a big unit cell volume at the same time, as indicated by the isotope effect and hydrogenation experiments.The discovery of superconductivity at 40 K in MgB 2 ͑Ref. 1͒ has attracted intense scientific interest towards modifying the structural and electronic properties of this material to improve its critical transition temperature T c . Although some possible routes to increase the T c , 2-7 such as increasing the phonon frequency, increasing the density of states, and expanding the unit cell volume, have been employed in the Mg-B system, all attempts to modify the MgB 2 host lattice to further increase T c have failed. It seems that most factors which influence the superconductivity of MgB 2 have already been optimized in the pure Mg-B system. Chemical substitution, a method to change several physical properties, such as the electron density, crystal lattice parameters, and the disorder effect, has been well investigated by different groups. On the fact of T c depression, Takenobu et al. 8 and Lee et al. 9 explain it as due to crystal lattice contraction, electron doping induced electronic structure variation, and the disorder effect arising from substitution, while Kortus et al. 10 ascribe the T c depression to band filling and interband scattering effects. It should be noted that Kazakov et al. 7 have suggested that the main issue is the competition between the effects of atomic size disorder, which causes the T c to decrease, and those of crystal lattice expansion, which tends to increase T c , which is in agreement with the positive T c dependence on unit cell volume for MgB 2 samples under pressure, as estimated by Deemyad et al. 11 However, in the case of Ag and Al codoped MgB 2 ͓Mg 1−2x ͑AgAl͒ x B 2 ͔, the a-axis and c-axis parameters increase with doping, and the volume V also increases, while the T c decreases with doping. 3 The authors attribute these characteristics to a disorder effect caused by the chemical substitution. 3 In a phonon-mediated superconductor, 12 it is well known that the T c is proportional to the averaged phonon frequency ͗͘, according to the McMillan formula. Factor group analysis predicts four modes at the ⌫ point of the Brillouin zone for the P6 / mmm space group in MgB 2 : a silen...

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Effect of Pb substitution in bulk superconducting MgB2

Cited by 11 publications

References 16 publications

Superconductivity of MgB₂in the BCS framework with emphasis on extrinsic effects on critical temperature

Superconductivity of MgB₂in the BCS framework with emphasis on extrinsic effects on critical temperature

Co-addition into MgB2: The structural and electronic properties of (MgB2)2−xCox

Raman study of element doping effects on the superconductivity ofMgB2

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Effect of Pb substitution in bulk superconducting MgB2

Cited by 11 publications

References 16 publications

Superconductivity of MgB2in the BCS framework with emphasis on extrinsic effects on critical temperature

Superconductivity of MgB2in the BCS framework with emphasis on extrinsic effects on critical temperature

Co-addition into MgB2: The structural and electronic properties of (MgB2)2−xCox

Raman study of element doping effects on the superconductivity ofMgB2

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Product

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Superconductivity of MgB₂in the BCS framework with emphasis on extrinsic effects on critical temperature

Superconductivity of MgB₂in the BCS framework with emphasis on extrinsic effects on critical temperature