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

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 ~400-580°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.