  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.
