Mechanochemically Assisted Synthesis of Ca/K 1144-Type Iron Pnictides.

The 1144 family of Iron Based Superconductors (IBSCs) is characterized by critical currents among the highest for single crystalline IBSCs. The synthesis of polycrystalline compounds is usually carried out through high temperature (T > 900 °C) processes. These methods, justified by a supposed thermodynamic instability of the 1144 phase at low temperature, are complicated by the presence of highly volatile elements and require fast heating and cooling steps. Here, it is shown how a High Energy Ball Milling (HEBM) treatment is effective to promote the reaction among the starting elements, thus favoring the synthesis of the 1144 phase at lower temperature. The evolution of the powders has been assessed for different milling times, observing the consumption of the starting reactants and the formation of crystalline pnictide phases. Different thermal treatments have been coupled to the HEBM treatment, allowing the study of the effect of time and temperature of the thermal step on the materials properties. It has been observed how the formation of the superconducting phase occurs on the HEBM samples at 500 °C and 600 °C. Critical temperatures comparable with data reported in the literature were obtained. Granularity phenomena and critical current density of sintered samples are highly dependent on the processing variables. [ABSTRACT FROM AUTHOR]