Carbon substitution in MgB 2 single crystals: Structural and superconducting properties

A comprehensive study of the effects of carbohydrate doping on the superconductivity of MgB 2 has been conducted. In accordance with the dual reaction model, more carbon substitution is achieved at lower sintering temperature. As the sintering temperature is lowered, lattice disorder is increased. Disorder is an important factor determining the transition temperature for the samples studied in this work, as evidenced from the correlations among the lattice strain, the resistivity, and the transition temperature. It is further shown that the increased critical current density in the high field region can be understood by a recentlyproposed percolation model [M. Eisterer et al., Phys. Rev. Lett. 90, 247002 (2003)]. For the critical current density analysis, the upper critical field is estimated from a correlation that was reported in a recent review article [M. Eisterer, Supercond. Sci. Technol. 20, R47 (2007)], where a sharp increase in the upper critical field by doping is mainly due to an increase in lattice disorder or impurity scattering. On the other hand, it is shown that the observed reduction in self-field critical current density is related to the reduction in the pinning force density by carbohydrate doping. KeywordsCorrelation, between, doping, induced, disorder, superconducting, properties, carbohydrate, doped, MgB2 Disciplines Engineering | Physical Sciences and Mathematics Publication DetailsKim, J, Dou, SX, Oh, S, Jercinovic, M, Babic, E, Nakane, T & Kumakura, H (2008), Correlation between doping induced disorder and superconducting properties in carbohydrate doped MgB2, Journal of Applied Physics, 104(6), 063911-1-063911-5. AuthorsJung Ho Kim, S X. Dou, Sangjun Oh, M Jercinovic, E Babic, T Nakane, and Hiroaki Kumakura A comprehensive study of the effects of carbohydrate doping on the superconductivity of MgB 2 has been conducted. In accordance with the dual reaction model, more carbon substitution is achieved at lower sintering temperature. As the sintering temperature is lowered, lattice disorder is increased. Disorder is an important factor determining the transition temperature for the samples studied in this work, as evidenced from the correlations among the lattice strain, the resistivity, and the transition temperature. It is further shown that the increased critical current density in the high field region can be understood by a recently-proposed percolation model ͓M. Eisterer et al., Phys. Rev. Lett. 90, 247002 ͑2003͔͒. For the critical current density analysis, the upper critical field is estimated from a correlation that was reported in a recent review article ͓M. Eisterer, Supercond. Sci. Technol. 20, R47 ͑2007͔͒, where a sharp increase in the upper critical field by doping is mainly due to an increase in lattice disorder or impurity scattering. On the other hand, it is shown that the observed reduction in self-field critical current density is related to the reduction in the pinning force density by carbohydrate doping.

Section: Resultsmentioning

confidence: 83%

Correlation between doping induced disorder and superconducting properties in carbohydrate doped MgB2

Kim

Dou

et al. 2008

“…5,11 In both cases ͑SiC and CNT͒ part of carbon dissolves into the MgB 2 structure during the fabrication process, 13,19 and the shift in the a-lattice parameter, obtained from x-ray diffraction, can be used as a measure of the actual amount of C ͑x͒ in the Mg͑B 1−x C x ͒ 2 structure. 22 The synthesis temperature, lattice parameters, and x values obtained from fitting the single crystal data of Kazakov et al 25 and the neutron diffraction data of Avdeev et al 27 are listed in Table I. Figure 1 shows the normalized dc magnetization as a function of temperature ͑T͒, measured with a Quantum Design® superconducting quantum interference design magnetometer, in a field of 20 Oe using a zero field cooling process.…”

Section: Methodsmentioning

confidence: 99%

“…Although the effect of carbon substitution is one of the most studied in MgB 2 , the results on C solubility and the effect of C doping on T c , J c , and H c2 reported so far vary significantly, due to precursor materials, fabrication techniques, and processing conditions used. [20][21][22][23][24][25] Recently, Matsumoto et al 26 reported that J c in SiC-alloyed MgB 2 tapes depends on a complex relation between grain connectivity, H c2 , and flux pinning induced by grain boundaries and precipitates. However, the distinct effect of C incorporation through different routes in J c and H c2 is still not entirely understood.…”

Section: Introductionmentioning

confidence: 99%

SiC and carbon nanotube distinctive effects on the superconducting properties of bulk MgB2

Serrano

Serquis

Dou

et al. 2008

This work describes in detail the simultaneous enhancement of the upper critical field ͑H c2 ͒ and the critical current density ͑J c ͒ of MgB 2 bulk samples doped with nano-SiC particles, as well as single-walled and double-walled ͑dw͒ carbon nanotubes ͑CNTs͒. The magnetization properties were examined in a superconducting quantum interference device magnetometer, and four-probe transport measurements were performed using a 50 T pulsed magnet to determine H c2 ͑T͒. We found that the J c enhancement is similar in all doped samples at 5 K but nano-SiC addition is more effective to improve the flux pinning in the high temperature range ͑T ജ 20 K͒; this improvement cannot solely be attributed to the C incorporation to the lattice but also to the presence of other types of defects ͑i.e., several kinds of nanoinclusions͒. CNTs produce a better C incorporation that is more effective to enhance H c2 ͓i.e., dwCNT-doped samples reached a record H c2 ͑0͒ϳ44 T value for bulk MgB 2 ͔. All the H c2 ͑T͒ curves obtained for different types of doping can be successfully described using a model for a two-gap superconductor in the dirty limit.

“…It is well documented that B c2 can be enhanced significantly by various techniques [1,2,3,4,5,6,7,8,9,10,11]. Although the mechanisms involved in these changes are not yet fully understood, impurity scattering in both bands seems to play a major role.…”

Section: Consequences/strategymentioning

confidence: 99%

“…In MgB 2 thermal effects should play only a minor role due to its comparatively low Ginzburg number. Nevertheless, the critical currents become too small for power applications at fields well below H c2 , even at 4.2 K. Fortunately, the upper critical field of MgB 2 can be rather easily enhanced by certain preparation conditions [1,2,3], doping [4,5,6,7,8] or irradiation [9,10,11], and exceeds 30 T (at 0 K). Even for such "high-H c2 " materials, the application range is limited to around 10 T in polycrystalline samples.…”

Section: Introductionmentioning

confidence: 99%

Influence of the upper critical-field anisotropy on the transport properties of polycrystalline MgB2

Eisterer

Krutzler

Weber

2005

The intrinsic properties of MgB2 form the basis for all applications of this superconductor. We wish to emphasize that the application range of polycrystalline MgB2 is limited by the upper critical field Hc2 and its anisotropy. In wires or tapes, the MgB2 grains are randomly oriented or only slightly textured and the anisotropy of the upper critical field leads to different transport properties in different grains, if a magnetic field is applied and the current transport becomes percolative. The irreversibility line is caused by the disappearance of a continuous superconducting current path and not by depinning as in high temperature superconductors. Based on a percolation model, we demonstrate how changes of the upper critical field and its anisotropy and how changes of flux pinning will influence the critical currents of a wire or a tape. These predictions are compared to results of neutron irradiation experiments, where these parameters were changed systematically.