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Inter- and intragranular nanostructure and possible spinodal decomposition in low-resistivity bulk MgB2 with varying critical fields

Published online by Cambridge University Press:  03 March 2011

Xueyan Song*
Affiliation:
Applied Superconductivity Center, University of Wisconsin-Madison, Madison, Wisconsin 53706
Valeria Braccini
Affiliation:
Applied Superconductivity Center, University of Wisconsin-Madison, Madison, Wisconsin 53706; and I.N.F.M-LAMIA, Dipartimento di Fisica, Via Dodecaneso 33, 16146 Genova, Italy
David C. Larbalestier
Affiliation:
Applied Superconductivity Center, University of Wisconsin, Madison, Wisconsin 53706
*
a) Address all correspondence to this author. e-mail: xsong@wisc.edu
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Abstract

Three electromagnetically well-characterized bulk samples with nominal resistivities at 40 K [ρ(40 K)], varying from 1 to 18 μΩcm, were investigated by conventional and high-resolution transmission electron microscopy. Clean, coherent, or semi-coherent grain boundaries and dirty-grain boundaries wetted by amorphous phases were found in all three samples, even though the starting sample A had the very low resistivity of 1 μΩcm at 40 K, characteristic of clean-limit samples. Taking into account its porosity and wetted-grain boundary area, the true resistivity value is about 0.5 μΩcm. Additional samples B and C, prepared by exposing sample A to Mg vapor, showed enhanced ρ(40 K) values of 14 and 18 μΩcm, without noticeable change in either inter- or intra-granular microstructure. Intragranular nanoprecipitates with characteristics of a spinodal of MgB7, with a size of 1–5 nm, were observed in a few areas of samples A and B at high local density; however at too low an overall density to explain the increased resistivities and upper critical fields.

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Articles
Copyright
Copyright © Materials Research Society 2004

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References

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