Lattice Distortion and Magnetic Order in Ca$_{10}$(Fe$_{2}$As$_{2}$)$_{5}$(Pt$_{3}$As$_{8}$)*

The Ca$_{\mathrm{10}}$(Fe$_{\mathrm{2}}$As$_{\mathrm{2}})_{\mathrm{5}}$(Pt$_{\mathrm{3}}$As$_{\mathrm{8}})$ compound is a member of the Fe-based high-temperature superconductor family. Recent work showed that this compound has a complex chemical structure with a skutterudite-type Pt-As intermediary layer sandwiched between tetrahedral Fe-As layers. We have studied the structural and magnetic properties of Ca$_{\mathrm{10}}$(Fe$_{\mathrm{2}}$As$_{\mathrm{2}})_{\mathrm{5}}$(Pt$_{\mathrm{3}}$As$_{\mathrm{8}})$ by single-crystal x-ray and neutron diffraction. Similar to other compounds in the iron arsenide family, we observed a lattice distortion from tetragonal to orthorhombic symmetry below approximately 110 K and stripe-like antiferromagnetic order below approximately 100 K. Both phase transitions are 2$^{\mathrm{nd}}$ order in nature. The magnetic order and lattice distortion in the iron arsenides appear to be robust against deviations from simple structure motifs.