Synchrotron X-ray Diffraction Study of Structural Phase Transition in   Ca10(Ir4As8)(Fe2-xIrxAs2)
  We report a structural transition found in Ca10(Ir4As8)(Fe2-xIrxAs2)5, which exhibits superconductivity at 16 K. The c-axis parameter is doubled below a structural transition temperature of approximately 100 K, while the tetragonal symmetry with space group P4/n (No.85) is unchanged at all temperatures measured. Our synchrotron x-ray diffraction study clearly shows iridium ions at a non-coplanar position shift along the z-direction at the structural phase transition. We discuss that the iridium displacements affect superconductivity in Fe2As2 layers. 
Naoyuki Katayama, Kento Sugawara, Yuki Sugiyama, Takafumi Higuchi,   Kazutaka Kudo, Daisuke Mitsuoka, Takashi Mizokawa, Mino...
cond-mat.supr-con