Effect of the sintering temperature on the microstructure of MgB2 bulks manufactured by in-situ technique

Abstract

Besides many interesting features of MgB₂, it is important for the green economy of the future that it allows systems that use L-Ne or L-H₂ instead of cryogens; meanwhile as a light material, it can attract attention in terms of portable applications and especially space applications. MgB₂ bulks and wires are produced by various processing techniques that can be categorized as either in-situ or ex-situ methods. Both have their own advantages and disadvantages. Therefore, the decision on which method to use should be evaluated according to the needs of the application. For the good inter-grain connectivity, in-situ production should be chosen but improved. Instead of high temperatures and long heat treatment duration, examining the effect of relatively lower and shorter times on the material was deemed necessary for the optimization of the in-situ method.

For this reason, in this study, microstructural examination of bulk MgB₂ samples produced by in-situ method at 625, 650 and 700 °C for 6 and 12 hours, was carried out. The samples microstructural properties were investigated by XRD and SEM measurements. XRD measurements were performed between 20° and 80° with step size of 0.02° from the pellet surface. The crystallographic refinement was simulated using the Full Prof software by the Rietveld method. Lattice parameter and cell volume, phase fractions were determined. The crystallite size is calculated from the XRD results using the Debye-Scherrer formula. Magnetic T_c,mag was determined as around 38,5 K from the magnetization measurement. The results provide guideline for further optimization of the microstructure of bulk MgB₂ with enhanced properties.