ISSN 1061-3862, International Journal of Self-Propagating High-Temperature Synthesis, 2007, Vol. 16, No. 4, pp. 207–212. © Allerton Press, Inc., 2007.
Structural Characterization and Superconducting Properties of MgB2 Prepared by SHS-Method W. Ramdanea, B. Bendjemila, b, A. Hafsa, A. Hendaouia, M. Gueriounea, and D. Vrelc a Laboratoire
d’Etude et de Recherche des Etats Condensés (LEREC), Département de Physique, Université de Annaba, Algérie b Département de Mécanique, Faculté des Sciences et de l’Ingénieries, Université 8 Mai 1945 Guelma, Algérie c Laboratoire d’Ingénierie des Matériaux et des Hautes Pressions (LIMHP), UPR CNRS 1311-Université Paris Nord, Institut Galilée 99 Avenue Jean-Baptiste Clément 93430 Villetaneuse, France e-mail:
[email protected] Received September 17, 2007
Abstract—Self-propagating high-temperature synthesis (SHS) of bulk MgB2 superconductor from Mg-2B powder blend is reported. This reaction proceeds violently at 100 A under a protective atmosphere. Since the heat of reaction of Mg and B was not enough for chain reaction, then (Ti + C) mixed powders were used as the ignition agent to assist the reaction (Mg + 2B). In this case, the combustion front moved without any difficulty. The diffraction lines of the product can be indexed to a hexagonal MgB2 phase, with lattice constants a = 3.0845 Å, and c = 3.5259 Å. For comparison, the direct synthesis of (Mg + 2B) mixture was carried out at (800°C–1000°C). It can be found, that high-temperature sintering (1000°C) will induce the formation of impurities. The MgB2 grains are fine, well compacted and more homogenous. The structure of materials was studied using XRD, FESEM and EDX. M-H curvatures were measured under the magnetic fields between –80 kOe and 80 kOe. Jc was calculated from width of magnetization hysteresis loops based on the extended Bean Model. Keywords: SHS method; MgB2; superconductivity; grain connectivity; critical current density (Jc); microstructure-final; magnetic susceptibility. PACS numbers: 81.20.Ka, 74.70.-b, 75.50.-y DOI: 10.3103/S1061386207040061
1. INTRODUCTION MgB2 is a type II superconductor with a highly anisotropic coherence length, penetration depth, critical fields and other electronic superconducting and normal state characteristics [1, 2]. The intrinsic characteristics of MgB2 make up this material a very promising candidate for technological uses, although the low value of the irreversibility field [3, 4] and the steep decrease of the critical current density (Jc) with increasing magnetic field [4, 5] considerably lessen its potentiality for applications. In addition, as revealed by the irreversible magnetization experiment [6, 7] the behavior in the magnetic hysteresis loops of MgB2 is dominated by bulk pinning [8, 7]. According to the literature data, MgB2 has been prepared in various forms (bulk, single crystals, thin films, tapes and wires) [9]. The significant difference in melting temperatures between Mg (650°C) and B (2030°C) consequentially induces a large difference of diffusion behavior. Therefore, Mg can exist as solid, liquid or gas state during reaction with B [10]. In the present paper, we report the direct high-temperature synthesis of (Mg + 2B) mixture at (800°C–1000°C) and the self-propagating high-tem-
perature synthesis (SHS) of MgB2. In the later case, a mixture of (Ti + C) was used to assist the ignition of this reaction. The advantage of this method is shown by comparing structural properties of MgB2 synthesized both by SHS and the classical high-temperature interaction. 2. EXPERIMENTAL PROCEDURE In this work, fine Mg (
