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- Title
Thermodynamic and kinetic evidence for MgO formation and pinning behavior in glycine-doped MgB bulks.
- Authors
Cai, Qi; Guo, Qianying; Liu, Yongchang; Ma, Zongqing; Li, Huijun
- Abstract
The formation and role of MgO impurity phase in the glycine (Gly; CHNO)-doped MgB were investigated by preparing the samples from multiple routes. On the contrary to the observation that the dielectric MgO aggregates at the grain boundary and deteriorates the superconductivity in the un-doped system, the MgO particles in the Gly-doped system dispersed uniformly on the MgB matrix and provided enhanced effect on the critical current density. Thermodynamic and kinetic (Ozawa-Flynn-Wall method) analyses were carried out by in situ X-ray diffraction (in situ XRD) and differential scanning calorimetry (DSC) techniques, which proved that the formation of MgO is owing to the reaction between Mg and the decomposition product of Gly (CO) in advance. Due to this prior reaction, the solid-solid Mg-B reaction followed the first-order reaction mechanism in the Gly-doped MgB, rather than the second-order Avrami-Erofeev mechanism, which is accorded by the un-doped sample. This reaction 2 Mg + CO → 2 MgO + C is analogous to the dual reaction mechanism 2Mg + SiC → MgSi + C in the SiC-doped MgB, and similarly the MgO served as effective pinning centers and enhanced the critical current density in the Gly-doped MgB, while the C atoms provided the scattering effect and improved the upper critical field. Combined with the effect of histidine on the superconductivity of MgB, we summed up the requirements for an amino acid to be an effective dopant.
- Subjects
THERMODYNAMICS; MAGNESIUM oxide; RING formation (Chemistry); DISLOCATION pinning; GLYCINE; MAGNESIUM
- Publication
Journal of Materials Science, 2016, Vol 51, Issue 5, p2665
- ISSN
0022-2461
- Publication type
Article
- DOI
10.1007/s10853-015-9580-1