Hostname: page-component-848d4c4894-nr4z6 Total loading time: 0 Render date: 2024-05-21T13:57:45.824Z Has data issue: false hasContentIssue false

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*
Applied Superconductivity Center, University of Wisconsin-Madison, Madison, Wisconsin 53706
Valeria Braccini
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
Applied Superconductivity Center, University of Wisconsin, Madison, Wisconsin 53706
a) Address all correspondence to this author. e-mail:
Get access


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.

Copyright © Materials Research Society 2004

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)



1.Mazin, I.I. and Antropov, V.P.: Electronic structure, electron– phonon coupling, and multiband effects in MgB2. Physica C 385, 49 (2003).CrossRefGoogle Scholar
2.Gurevich, A.: Enhancement of the upper critical field by nonmagnetic impurities in dirty two-gap superconductors. Phys. Rev. B 67, 184515 (2003).CrossRefGoogle Scholar
3.Gurevich, A., Patnaik, S., Braccini, V., Kim, K.H., Milke, C., Song, X., Cooley, L.D., Bu, S.D., Kim, D.M., Choi, J.H., Belenky, L.J., Giencke, J., Lee, M.K., Tian, W., al., et: Very high upper critical fields in MgB2 produced by selective tuning of impurity scattering. Supercond. Sci. Technol . 17, 278 (2004).CrossRefGoogle Scholar
4.Rowell, J.M.: The widely variable resistivity of MgB2 samples. Supercond. Sci. Technol. 16 R17 (2003).CrossRefGoogle Scholar
5.Ribeiro, R.A., Bud’ko, S.L., Petrovic, C. and Canfield, P.C.: Effects of boron purity, Mg stoichiometry and carbon substitution on properties of polycrystalline MgB2. Physica C 385, 16 (2003).CrossRefGoogle Scholar
6.Bellingeri, E., Malagoli, A., Modica, M., Braccini, V., Siri, A.S. and Grasso, G.: Neutron-scattering studies of superconducting MgB2 tapes. Supercond. Sci. Technol. 16, 276 (2003).CrossRefGoogle Scholar
7.Braccini, V., Cooley, L.D., Patnaik, S., Larbalestier, D.C., Manfrinetti, P., Palenzona, A. and Siri, A.S.: Significant enhancement of irreversibility field in clean-limit bulk MgB2. Appl. Phys. Lett. 81, 4577 (2002).CrossRefGoogle Scholar
8.Hirth, J.P. and Lothe, J.Theory of dislocations, 2nd ed, (Wiley, New York, 1982), pp. 705.Google Scholar
9.Edington, J.W.Practical Electron Microscopy in Materials Science, Monographs 3, (N. V. Philips, Eindhoven, 1976) p. 50.Google Scholar
10.Gao, Y., Merkle, K.L., Bai, G., Chang, H.L.M. and Lam, D.J.: [001] tilt grain-boundaries in YBa2Cu3O7-x thin-films. Ultramicroscopy 37, 326 (1991).CrossRefGoogle Scholar
11.Li, S., White, T., Laursen, K., Tan, T.T., Sun, C.Q., Dong, Z.L., Li, Y., Zho, S.H., Horvat, J. and Dou, S.X.: Intens vortex pinning enhanced by semicrystalline defect traps in self-aligned nanostructured MgB2. Appl. Phys. Lett. 83, 314 (2003).CrossRefGoogle Scholar
12.Verhoeven, J.D.Fundamentals of Physical Metallurgy, (Wiley, New York, 1975) pp. 379.Google Scholar
13.Song, X., Babcock, S.E., Eom, C.B., Larbalestier, D.C., Regan, K.A., Cava, R.J., Bud’Ko, S.L., Canfield, P.C. and Finnemore, D.K.: Anisotropic grain morphology, crystallographic texture and their implications for flux pinning mechanisms in MgB2 pellets, filaments and thin films. Supercond. Sci. Technol. 15, 511 (2002).CrossRefGoogle Scholar
14.Zhu, Y., Wu, L., Volkov, V., Li, Q., Gu, G., Moodenbaugh, A.R., Malac, M., Suenaga, M. and Tranquada, J.: Microstructure and structural defects in MgB2 superconductor. Physica C 356, 239 (2001).CrossRefGoogle Scholar
15.Klie, R.F., Idrobo, J.C., Browning, N.D., Regan, K.A., Rogado, N.S. and Cava, R.J.: Direct observation of nanometer-scale Mg- and B-oxide phases at grain boundaries in MgB2. Appl. Phys. Lett. 79, 1837 (2001).CrossRefGoogle Scholar
16.Larbalestier, D.C., Cooley, L.D., Rikel, M.O., Polyanskii, A.A., Jiang, J., Patnaik, S., Cai, X.Y., Feldmann, D.M., Gurevich, A., Squitieri, A.A., Naus, M.T., Eom, C.B., Hellstrom, E.E., Cava, R.J., Regan, K.A., Rogado, N., Hayward, M.A., He, T., Slusky, J.S., Khalifah, P., Inumaru, K. and Haas, M.Strongly linked current flow in polycrystalline forms of the superconductor MgB2. Nature 410, 186 (2001).CrossRefGoogle ScholarPubMed
17.Clarke, D.R.: On the equilibrium thickness of intergranular glass phases in ceramic materials. J. Am. Ceram. Soc. 70, 15 (1987).CrossRefGoogle Scholar
18.Kingery, W.D., Bowen, H.K. and Uhlmann, D.R.Introduction to Ceramics, 2nd Edition, (John Wiley & Sons, 1976), p. 209.Google Scholar
19.Chisholm, M.F. and Smith, D.A.: Low-angle tilt grain boundaries in YBa2Cu3O7 superconductors. Philos. Mag. A . 59, 181 (1989).CrossRefGoogle Scholar
20.Brutti, S., Ciccioli, A., Balducci, G., Gigli, G., Manfrinetti, P. and Palenzona, A.: Vaporization thermodynamics of MgB2 and MgB4. Appl. Phys. Lett. 80, 2892 (2002).CrossRefGoogle Scholar
21.Lee, S.: Crystal growth of MgB2. Physica C 385, 31 (2003).CrossRefGoogle Scholar
22.Naslain, R., Guette, A. and Barret, M.: Sur le diborure et le tétraborure de magnésium. Considérations cristallochimiques sur les tétraborures. J. Solid State Chem. 8, 68 (1973).CrossRefGoogle Scholar
23.Guette, A., Barret, M., Naslain, R., Hagenmuller, P., Tergenius, L.E. and Lundstrom, T.: Crystal structure of magnesium heptaboride Mg2B14. J. Less-Comm. Met. 82, 325 (1981).CrossRefGoogle Scholar
24.Matkovich, V.I. and Economy, J.: Structure of MgAlB14 and a brief critique of structural relationships in higher borides. Acta Crystallogr. B 26, 616 (1970).CrossRefGoogle Scholar
25.Hinks, D.G., Jorgensen, J.D., Zheng, H. and Short, S.: Synthesis and stoichiometry of MgB2. Physica C 382, 166 (2002).CrossRefGoogle Scholar
26.Cava, R.J., Zandbergen, H.W. and Inumarua, K.: The substitutional chemistry of MgB2. Physica C 385, 8 (2003).CrossRefGoogle Scholar
27.Liao, X.Z., Serquis, A., Zhu, Y.T., Huang, J.Y., Civale, L., Peterson, D.E., Mueller, F.M. and Xu, H.F.: Mg(B,O)2 precipitation in MgB2. J. Appl. Phys. 93, 6208 (2003).CrossRefGoogle Scholar
28.Klie, R.F., Idrobo, J.C., Browning, N.D., Serquis, A., Zhu, Y.T., Liao, X.Z. and Mueller, F.M.: Observation of coherent oxide precipitates in polycrystalline MgB2. Appl. Phys. Lett. 80, 3970 (2002).CrossRefGoogle Scholar
29.Dou, S.X., Braccini, V., Soltanian, S., Klie, R., Zhu, Y., Li, S., Wang, X.L. and Larbalestier, D. Nanoscale-SiC doping for enhancing Jc and Hc2 in the Superconducting MgB2, cond-mat/0308265.Google Scholar
30.Finnemore, D.K., Ostenson, J.E., Bud’ko, S.L., Lapertot, G. and Canfield, P.C.: Thermodynamic and transport properties of superconducting Mg10B2. Phys. Rev. Lett. 86, 2420 (2001).CrossRefGoogle ScholarPubMed
31.Canfield, P.C., Finnemore, D.K., Bud’ko, S.L., Ostenson, J.E., Lapertot, G., Cunningham, C.E. and Petrovic, C.: Superconductivity in dense MgB2 wires. Phys. Rev. Lett. 86, 2423 (2001).CrossRefGoogle ScholarPubMed
32.Avdeev, M., Jorgensen, J.D., Ribeiro, R.A., Bud’ko, S.L. and Canfield, P.C.: Crystal chemistry of carbon-substituted MgB2. Physica C 387, 301 (2003).CrossRefGoogle Scholar
33.Ribeiro, R.A., Bud’ko, S.L., Petrovic, C. and Canfield, P.C.: Carbon doping of superconducting magnesium diboride. Physica C 384, 227 (2003).CrossRefGoogle Scholar
34.Pogrebnyakov, A.V., Redwing, J.M., Jones, J.E., Xi, X.X., Xu, S.Y., Li, Qi, Vaithyanathan, V. and Schlom, D.G.: Thickness dependence of the properties of epitaxial MgB2 thin films grown by hybrid physical-chemical vapor deposition. Appl. Phys. Lett. 82, 4319 (2003).CrossRefGoogle Scholar
35.Serquis, A., Zhu, Y.T., Peterson, E.J., Coulter, J.Y., Peterson, D.E. and Mueller, F.M.: Effect of lattice strain and defects on the superconductivity of MgB2. Appl. Phys. Lett. 79, 4399 (2001).CrossRefGoogle Scholar