The voltage–current relations for MgB 2 obtained by reactive liquid infiltration G. Giunchi a, * , S. Raineri a , R. Wesche b , P.L. Bruzzone b a EDISON Spa, R&D, Via U. Bassi 2, 20159 Milan, Italy b EPFL, CRPP, Villigen PSI, Switzerland Abstract The reactive liquid infiltration (RLI) technique, applied to the MgB 2 material, has allowed us to obtain either bulk or wire samples of good transport properties. The evaluation of the voltage–current characteristics, V –I n , for typical samples, measured by transport at temperatures between 4.2 and 30 K, is presented. The behaviour of the n exponent is discussed in terms of a simple model and the differences between bulk and wire samples are outlined. Ó 2003 Elsevier B.V. All rights reserved. Keywords: Bulk MgB 2 ; Flux flow; Critical current density; Activation energy; n-factor 1. Introduction The two main routes to prepare MgB 2 are based on the reaction of the pure elements (‘‘in situ’’ technique) or the sintering of MgB 2 powders (‘‘ex situ’’ technique). Our ‘‘reactive liquid infil- tration’’ (RLI) [1] is a variant of the in situ tech- nique essentially based on the reactive diffusion of liquid Mg into boron powders maintained in a tightly closed metallic container. The volume of the MgB 2 product is only slightly higher than the volume initially occupied by the packed boron powders, so that the shape of the final manufact mimics the shape of the boron preform. Applying the RLI technique in several different ways, we have realized either bulk manufacts of different shapes [2], or hollow wires [3], both characterised by excellent high density and critical current den- sities comparable to the values obtained with other manufacturing techniques without the use of a high pressure apparatus. The aim of this study is to investigate the V ðI Þ behaviour, as a function of the temperature and of the applied magnetic field, for different MgB 2 manufacts obtained with the RLI technology. The V ðI Þ behaviour is described with the usual power law V –I n . The knowledge of the n-factor is for example of great interest in the design of resistive fault current limiters. 2. Experimental In this work the properties of a new MgB 2 bulk sample (A-#62), prepared as described in the * Corresponding author. Tel.: +39-02-62223194; fax: +39-02- 62223074. E-mail address: giovanni.giunchi@edison.it (G. Giunchi). 0921-4534/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2003.09.061 www.elsevier.com/locate/physc Physica C 401 (2004) 310–315