Structural properties and superconductivity of SrFe₂As _{2 - X}P_x (0.0 ≤ x ≤ 1.0) and CaFe₂As _{2 - Y}P_y (0.0 ≤ y ≤ 0.3)

The SrFe₂As_{2 - x}P_x (0.0 ≤ x ≤ 1.0) and CaFe₂As_{2 - y}P_y (0.0 ≤ y ≤ 0.3) materials were prepared by a solid-state reaction method. X-ray diffraction measurements indicate that the single-phase samples can be successfully obtained for SrFe₂As_{2 - x}P_x (0.0 ≤ x ≤ 0.8) and CaFe₂As_{2 - y}P_y (0.0 ≤ y ≤ 0.3). Visible contraction of the lattice parameters is determined due to the relatively smaller radius of P ions in comparison with that of As. The spin-density-wave (SDW) instability associated with the tetragonal to orthorhombic phase transition is suppressed noticeably in both systems following the increase in P content. The highest superconducting transitions are observed at about 27K in SrFe₂As_1.3P_0.7 and at about 13K in CaFe ₂As_1.925P_0.075, respectively. Structural analysis suggests that lattice contraction could notably affect the superconductivity in these materials.