Suppression of magnetism and development of superconductivity within the collapsed tetragonal phase of Ca[subscript 0.67]Sr[subscript 0.33]Fe[subscript 2]As[subscript 2] under pressure

Structural and electronic characterizations of (Ca{sub 0.67}Sr{sub 0.33})Fe{sub 2}As{sub 2} have been performed as a function of pressure up to 12 GPa using conventional and designer diamond anvil cells. The compound (Ca{sub 0.67}Sr{sub 0.33})Fe{sub 2}As{sub 2} behaves intermediately between its end members, displaying a suppression of magnetism and the onset of superconductivity. Like other members of the AFe{sub 2}As{sub 2} family, (Ca{sub 0.67}Sr{sub 0.33})Fe{sub 2}As{sub 2} undergoes a pressure-induced isostructural volume collapse, which we associate with the development of As-As bonding across the mirror plane of the structure. This collapsed tetragonal phase abruptly cuts off the magnetic state and supports superconductivity with a maximum T{sub c} = 22.2 K. The maximum T{sub c} of the superconducting phase is not strongly correlated with any structural parameter, but its proximity to the abrupt suppression of magnetism as well as the volume-collapse transition suggests that magnetic interactions and structural inhomogeneity may play a role in its development.