Optimization of Phase Formation and Superconducting Properties in MgB 2 Prepared by Phase Transformation from MgB 4

Author： Tan K.

ISSN： 1543-186X

Source： Journal of Electronic Materials, Vol.41, Iss.4, 2012-04, pp. : 673-678

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Abstract

In this work, polycrystalline MgB₄ was prepared, and then the presence of MgO in the powder was reduced by acid leaching. To synthesize MgB₂, the MgB₄ powder was reacted with Mg at temperatures from 650°C to 950°C for 4 h and 8 h. Using the Rietveld method, the MgB₂ phase was estimated to be in greater proportion over the sintering temperature range of 650°C to 750°C, above which it decreased rapidly, accompanied by the formation of more of the MgB₄ phase. Scanning electron microscopy showed that the samples have reduced porosity compared with those synthesized by the direct reaction of (Mg + 2B). Upon increasing the sintering temperature, the superconducting transition temperature decreased, which is attributed to lattice distortion. The results of this work demonstrate that control of heat treatment is essential to optimize the weight fraction of the MgB₂ phase and thereby increase the critical current density, J _c. The value of the magnetic J _c (5 K, 1 T) for the sample sintered at 750°C for 4 h is estimated to be 1.00 × 10⁵ A/cm².