Enhancement of Bc2 and Birr in bulk MgB2 superconductors with SnO2 Additions

• Published in: Physica. C, Superconductivity Vol. 578; p. 1
• Main Authors: Zhang, Danlu, Sumption, Michael D., Collings, Edward W., Thong, C.J., Rindfleisch, Matt A.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15-11-2020; Elsevier BV
• Subjects: Critical magnetic fields; Doping; Dwell time; Heat treatment; Lattice parameters; Lattice strain; Magnesium compounds; Magnesium diboride; Magnetic fields; Precipitates; SnO2 addition; Superconductivity; Superconductors; Tin dioxide; Transition temperature; Transition temperature; Magnesium diboride; SnO2 addition; Critical magnetic fields
• ISSN: 0921-4534; 1873-2143
• DOI: 10.1016/j.physc.2020.1353749

•The properties of MgB2 superconducting bulks with SnO2 additions were measured•BC2 was increased by 1.6 T and Birr was increased by 0.6 T at 20 K with 3 wt% SnO2 addition•The best BC2 (15.2 T at 20 K) obtained was comparable to that of optimized C-doped MgB2 bulks•In contrast to C doping, modest levels of SnO2 addition to MgB2 do not decrease Tc.
Three (MgB2)1-x(SnO2)x samples with x ranging from 0 to 5 wt% were prepared by the in situ route to study the effect of tin dioxide additions on the superconducting properties of MgB2 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 MgB2 phases with SnO2 addition. The magnitude of the a-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 MgB2 bulks which exhibited enhanced BC2. The upper critical fields (BC2) and the irreversibility fields (Birr) were measured resistively in fields up to 14 T at 5 K to Tc. The best BC2 value at 20 K (15.2 T based on extrapolation) was seen for sample IS3 (x =3 wt%), and was comparable to the best BC2 values (≈ 15 T at 20 K) seen for C-doped MgB2 bulks. IS3 had a corresponding Birr = 10.8 T (20 K). The superconducting transition temperature (Tc) appeared to increase slightly with doping, although within the range of error bars (37.4 K to 37.6 K for 1.6 T BC2 increase at 20 K), in contrast to C doping which is accompanied by a significant decrease in Tc (39 K to 36 K for 3.8 % C doped MgB2 bulk). We attribute the observed increase in both BC2 and Birr for SnO2-additions to lattice strain caused by the introduction of precipitates within the grains.