Phase formation and kinetic analysis of (Ba, K)Fe2As2 superconductor

Abstract

Abstract 122-type iron-based superconductors have attracted significant attention owing to their potential for high-field applications. Therefore, the study of the reaction mechanism is indispensable. In this work, the phase formation process and reaction kinetics of the Ba–K–Fe–As system were investigated in comparison with the Fe–As and Ba–Fe–As systems. Our findings suggest two main stages of the phase formation process: formation of the iron arsenide phase and its transformation to the 122-phase. It shows that FeAs forms slowly below 300 °C in the Ba–K–Fe–As system, and the formation significantly accelerates at ∼400 °C. KFe2As2 starts to generate at ∼640 °C and gradually transforms into Ba0.6K0.4Fe2As2. Furthermore, using the Flynn–Wall–Ozawa method and the Kissinger method, the kinetic parameters of the exothermic peak at ∼400 °C–580 °C for these three systems were obtained, including the most probable mechanism function f(α), apparent activation energy E, and apparent pre-exponential factor A. Our results suggest that all three systems exhibit complex reactions characterized by f(α) = (1 − α) n (1 < n < 2). The presence of the kinetic compensation effect in the three systems was discovered, implying similarities in their respective reaction mechanisms. Additionally, influence mechanism of K doping on the apparent activation energy and reaction rate was analyzed.