Polycrystalline samples of stoichiometric iron-based superconductors with CaKFe4As4, CaRbFe4As4, and CaCsFe4As4 compositions are synthesized by the mechanical alloying method, with their phase composition confirmed by X-ray diffraction analysis. The superconducting transition temperatures are found to be T₂^{{onset}} ≈ 34. 7, 35. 2, and 31. 3 К for CaKFe4As4, CaRbFe4As4, and CaCsFe4As4, respectively, with the transition widths being ΔTC ≈ 7. 6, 6. 4, and 6. 3 K. According to magnetic measurements and X-ray diffraction analysis, no impurity phases are detected in the CaKFe4As4 and CaRbFe4As4 sample.
Medvedev et al. (Mon,) studied this question.