Influence of oxygen doping on critical fields in MgB2 bulk superconductors
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Publisher:IOP Publishing Ltd
Citation:D. Zhang et. al. 2017 IOP Conf. Ser.: Mater. Sci. Eng. 279 012025. https://doi.org/10.1088/1757-899X/279/1/012025
In this work we studied the influence of SnO2 doping on the critical fields and temperatures of MgB2 bulk samples. Bulk samples were made by mixing ex-situ MgB2 powder with 5 wt% SnO2 powder and then pressing the mixed powders into pellets using a pressure of 2000 psi. The bulk pellets were sintered at 900⁰C in a furnace under flowing Ar. The samples were quenched to room temperature after dwelling at 900⁰C for 5h. XRD, SEM, and magnetic measurements were made on doped and control samples. XRD showed a decomposition of the SnO2 and very slight reductions in the a-axis and c-axis lattice parameters of theMgB2 phase. M-T (Magnetization-Temperature) curves showed a decrease in Bc2 of approximately 1 T in the temperature range of 24 K - 39 K with SnO2 additions as compared to the control samples.
An MgB2 bulk sample has been fabricated with 5 wt% SnO2 doping using an ex-situ processing route, and it has been compared to a control sample. SEM performed on the samples after powderizing shows similar grain structure in the doped and control sample. XRD measurements on the doped sample show no SnO2, but the presence of free Sn, indicating the decomposition of SnO2 during the reaction HT. XRD measurements show little or no change in c-axis lattice parameter, suggesting a lack of significant incorporation of oxygen into the lattice. A slight decrease in Bc2 and Birr was observed in the 24 K-39 K range. Addition of SnO2 has slightly decreased Bc2 and Birr of MgB2 given our particular preparation conditions of an ex-situ route and a 900 ⁰C reaction heat treatment. The mechanism is unclear, and may be connected either to the oxygen or the Sn from the decomposed SnO2. We have only explored one reaction temperature and one reaction type (ex-situ), which leaves a large amount of parameter space to explore. Given the promising results seen with previous in-situ work , we think oxygen additions are worth further exploration.
This work was supported by the National Institute of Biomedical Imaging and Bioengineering, under grant R01EB018363.