A new heat treatment to prepare high-quality polycrystalline and single crystal MgB2 in a single process

We report here on a new heat treatment to prepare both dense polycrystalline and single crystal MgB2 high quality samples in a single process. Resistivity measurements for the polycrystalline part of the sample gives a residual resistivity ratio RRR = 16.6 and a very low normal state resistivity ρ0(40 K) = 0.28 µcm. Both SEM and SQUID studies on polycrystals reveal the high quality, dense character and good coupling of the grain boundaries. On the other hand, the high-quality single crystals have a unique shape that resembles the hexagonal crystal structure. SQUID measurements reveal a very weak flux pinning character, implying that our single crystals are very clean, i.e. free from flux trapping centres. In this study, we conclude that heat treatment is playing a major role in defining the characteristics of both polycrystalline and single crystal MgB2. Samples are thoroughly characterized by x-ray, resistivity, dc SQUID and SEM.