The formation and crystallization of disordered nanosized ZnO resulting from the thermal decomposition of nanocrystalline hydrozincite [Zn5(CO3)2(OH)6] has been observed and investigated during pulse annealing experiments up to 625 °C in air or vacuum by electron paramagnetic resonance of trace amounts of substitutional Mn2+ impurity ions, in correlation with X-ray diffraction and transmission electron microscopy measurements. The mesoporous structure of the disordered ZnO, which initially forms in air and vacuum at 225 and 175 °C, respectively, further transforms into nanocrystalline ZnO of increasing particle size and improved lattice quality at higher annealing temperatures. The crystallization process, which does not affect the concentration of the substitutional impurity ions, as well as the simultaneous presence of both disordered and crystalline phases, should be considered in further applications of the resulting nanosized ZnO.

Superconductors are key materials for shielding quasi-static magnetic fields. In this work, we investigated the shielding properties of an MgB 2 cup-shaped shield with small aspect-ratio of height/outer radius. Shape and aspect-ratio were chosen in order to address practical requirements of both high shielding factors (SFs) and space-saving solutions. To obtain large critical current densities (J c ), which are crucial for achieving high magnetic-mitigation performance, a highpurity starting MgB 2 powder was selected. Then, processing of the starting MgB 2 powder into high density bulks was performed by spark plasma sintering. The as-obtained material is fully machinable and was shaped into a cup-shield. Assessment of the material by scaling of the pinning force showed a non-trivial pinning behaviour. The MgB 2 powder selection was decisive in enlarging the range of external fields where efficient shielding occurs. The shield's properties were measured in both axial-and transverse-field configurations using Hall probes. Despite a height/outer radius aspect ratio of 2.2, shielding factors higher than 10 4 at T=20 K up to a threshold field of 1.8 T were measured in axial-field geometry at a distance of 1 mm from the closed extremity of the cup, while SFs>10 2 occurred in the inner half of the cup. As expected, this threshold field decreased with increased temperature, but SFs still exceeding the above mentioned values were found up to 0.35 T at 35 K. The shield's shape limits the SF values achievable in transverse-field configuration. Nevertheless, the in-field J c of the sample supported SFs over 40 at T=20 K up to a field of 0.8 T, 1 mm away from the cup closure.

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