Magnetoresistivity and microstructure of YBa 2 Cu 3 O y prepared using planetary ball milling A. Hamrita, F. Ben Azzouz, A. Madani, M. Ben Salem ⇑ L3M, Department of Physics, Faculty of Sciences of Bizerte, University of Carthage, 7021 Zarzouna, Tunisia article info Article history: Received 11 March 2011 Received in revised form 29 September 2011 Accepted 4 October 2011 Available online 18 October 2011 Keywords: YBCO superconductor Planetary ball milling Electronic microscopy Transport properties abstract We have studied the microstructure and the magnetoresistivity of polycrystalline YBa 2 Cu 3 O y (YBCO or Y-123 for brevity) embedded with nanoparticles of Y-deficient YBCO, generated by the planetary ball milling technique. Bulk samples were synthesized from a precursor YBCO powder, which was prepared from commercial high purity Y 2 O 3 , Ba 2 CO 3 and CuO via a one-step annealing process in air at 950 °C. After planetary ball milling of the precursor, the powder was uniaxially pressed and subsequently annealed at 950 °C in air. Phase analysis by X-ray diffraction (XRD), granular structure examination by scanning elec- tron microscopy (SEM), microstructure investigation by transmission electron microscopy (TEM) coupled with energy dispersive X-ray spectroscopy (EDXS) were carried out. TEM analyses show that nanoparti- cles of Y-deficient YBCO, generated by ball milling, are embedded in the superconducting matrix. Electri- cal resistance as a function of temperature, q(T), revealed that the zero resistance temperature, T co , is 84.5 and 90 K for the milled and unmilled samples respectively. The milled ceramics exhibit a large magneto- resistance in weak magnetic fields at liquid nitrogen temperature. This attractive effect is of high signif- icance as it makes these materials promising candidates for practical application in magnetic field sensor devices. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction One of the features of high temperature superconducting mate- rials (HTS) is the broadening of the resistive transition under an ap- plied magnetic field. This broadening phenomenon opens a new line of research for using some of these superconducting materials as highly sensitive magnetic sensors [1]. The temperature range where polycrystalline HTS exhibit a significant magnetoresistivity effect is usually narrow and below liquid nitrogen temperature. Magnetoresistivity of HTS single crystals, wires, tapes, composites and films has been reported in both strong and weak magnetic fields [2–4]. YBCO based bulk composites exhibit a much higher sensitivity to weak magnetic fields at liquid nitrogen temperature compared to pure ceramics. This behavior is due to the high density of interfaces generated by the addition of a non-superconducting component in the superconducting matrix. Some studies of the ef- fect of nanosize inclusions in HTS cuprates on the magnetoresistiv- ity have been reported in the literature. An excess of added nanoparticles decreases the superconducting transition tempera- ture below that of liquid nitrogen [5]. The preparation method and the nature of the added nanoparticles may play an important role on the microstructure and on the electrical response of the superconducting materials under a magnetic field. The high energy ball-milling process, which was initially in- tended for ceramic strengthened alloys, has been successfully employed to the synthesis of different nanopowder materials including ferrites, ferroelectrics and superconducting materials. This technique has generated great interest because it uses low- cost and widely available oxides as starting materials. The milling process plays an important role on the microstructure develop- ment of the superconducting material. In the case of MgB 2 the high energy ball-milling technique facilitates the formation of an opti- mal microstructure with a high grain boundary density and lattice strain, which is expected to enhance the magnetic flux pinning ability and to improve the critical currents in external magnetic fields [6,7]. To our knowledge there is only one work devoted to the YBCO system reporting the effect of planetary ball milling on the super- conducting properties of YBCO [8]. Therefore, in this paper, we fo- cus on the microstructural evolution induced by planetary milling and its effect on the magnetoresistivity of YBCO. Our results can serve as a reference for further studies of planetary-milled YBCO powders for the manufacturing of superconducting films using spin coating. 0921-4534/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2011.10.003 ⇑ Corresponding author. Address: Faculté des Sciences de Bizerte, Département de Physique, 7021 Zarzouna, Tunisia. Tel.: +216 72 591 906; fax: +216 72 590 566. E-mail address: Mohamed.bensalem@fsb.rnu.tn (M. Ben Salem). Physica C 472 (2012) 34–38 Contents lists available at SciVerse ScienceDirect Physica C journal homepage: www.elsevier.com/locate/physc