Synthesis of CaKFe ₄ As ₄ bulk samples with high critical current density using a spark plasma sintering technique

Abstract

Abstract A high density CaKFe 4 As 4 bulk sample was successfully synthesized using a spark plasma sintering (SPS) technique. The density of the synthesized sample was 5.02 g cm −3 , corresponding to 96.2% of the theoretical density of CaKFe 4 As 4 . Moreover, a reasonably high Vickers hardness of 1 GPa was measured. The electrical resistivity of the SPS bulk sample was as low as approximately 600 μ Ω cm at 300 K, which is smaller than that of the ordinary sintered polycrystalline sample by nearly one order of magnitude, and exhibited a sharp superconducting transition with the transition width (Δ T c ) less than 2 K, indicating an improved grain connectivity. The critical current density of the SPS bulk sample calculated from the magnetization hysteresis loops (magnetic J c ) reached 18 kA cm −2 at 4.2 K under 5 T, which is the highest among the iron-based superconductor polycrystalline samples reported thus far.