The structure of the double-layer Ruddlesden-Popper phase ${\mathrm{Gd}}_2\mathrm{Sr}{\mathrm{Co}}_2{\mathrm{O}}_7$ has been determined in the temperature range $300–973\mathrm{K}$ using powder neutron diffraction. The room-temperature structure is tetragonal and displays small tilts of the oxygen sublattice that are described in $P{4}_2∕mnm$ symmetry instead of the idealized $I4∕mmm$ structure. A structural transition at $T\approx 580\mathrm{K}$ is characterized by reduction of unit cell symmetry and a marked axial elongation of the $\mathrm{Co}{\mathrm{O}}_6$ octahedra; this behavior is associated with a spin crossover at the octahedrally coordinated cobalt (III) ions, most likely from an intermediate to a high spin configuration.

• Received 3 July 2006

DOI:https://doi.org/10.1103/PhysRevB.75.024113