Enhancement of B c2 and B irr in bulk MgB 2 superconductors with SnO 2 Additions

Three (MgB ) (SnO ) samples with ranging from 0 to 5 wt% were prepared by the route to study the effect of tin dioxide additions on the superconducting properties of MgB bulk materials. All of the reacted samples were slightly Mg deficient although the starting Mg:B precursor powder ratio was 1:2. A heat treatment (HT) temperature of 700 °C with a dwell time of 30 min was used. XRD results showed evidence of peak shifts for MgB phases with SnO addition. The magnitude of the -axis lattice constant change (0.361 ± 0.075 %) calculated for the 3 wt% doped samples is comparable in magnitude to that seen previously for the C-doped MgB bulks which exhibited enhanced . The upper critical fields ( ) and the irreversibility fields ( ) were measured resistively in fields up to 14 T at 5 K to . The best value at 20 K (15.2 T based on extrapolation) was seen for sample IS3 (x = 3 wt%), and was comparable to the best values (≈ 15 T at 20 K) seen for C-doped MgB bulks. IS3 had a corresponding = 10.8 T (20 K). The superconducting transition temperature ( ) appeared to increase slightly with doping, although within the range of error bars (37.4 K to 37.6 K for 1.6 T increase at 20 K), in contrast to C doping which is accompanied by a significant decrease in (39 K to 36 K for 3.8 % C doped MgB bulk). We attribute the observed increase in both and for SnO -additions to lattice strain caused by the introduction of precipitates within the grains.