X-ray Micro-Tomography as a New and Powerful Tool for Characterization of MgB2 Superconductor

Abstract

Applied superconductivity is virtually important for all human activities solving different problems in the fields such as power and energy, electronics, computing and communications, medical equipment and sensors, fast transportation and so on. However, the progress in this field is relatively slow when compared to other young industries. The reasons are diverse, and among them are the prohibitive prices vs. performance of the superconducting technologies. In this regard, superconducting-based materials or products with improved working characteristics at constant or lower prices are always of interest. One superconductor of practical interest is MgB2. This superconductor has several advantages as follows: 1. Critical temperature Tc = 39 K of MgB2 [1] is the highest among simple superconducting compounds. This is a unexpectedly high Tc and, although MgB2 can be considered a swave classical Bardeen-Cooper-Schriffer (BCS) superconductor, it shows elements of unconventional superconductivity: two-gap superconductivity was observed with gap values of Δσ = 7.4 meV and Δπ = 2.1 meV at 4.2 K corresponding to critical temperatures of 15 K and 45 K, with σ and π being the bands of the boron electrons [2]. In fact, there are two hole-type quasi-two-dimensional σ bands (σ1 and σ2), an electron-type (π 1) and a hole-type (π 2) three-dimensional π bands [3,4]. Such situation generates new physical effects with markedly different behaviors in many properties some of them of practical meaning when compared with single band superconductors. 2. It is a simple compound composed of only two elements. 3. It is a cheap compound composed of relatively cheap and available elements. 4. It is not toxic and it is considered stable in the air. 5. It is a light compound with low theoretical density of 2.63 g/cm3. Crystal structure is relatively simple of layered hexagonal type. 6. It has anisotropy, but it is not as high as in high temperature superconductors.