Neutron-diffraction study of the crystal structure of Ca 1.5 Sr 0.5 RuO 4

We have investigated the temperature dependence of the crystal structure of Ca1.5Sr0.5RuO4 by powder and single-crystal neutron diffraction in the temperature range from 1.5 to 300 K. Both an anomaly in the temperature dependence of the c lattice parameter and the observation of characteristic superstructure reflections indicate a continuous transition from the I41/acd structure, in which the corner-sharing RuO6 octahedra are rotated about the c axis, to a low-temperature phase with an additional rotation of the octahedra around an axis lying in the RuO2 planes. The occurrence of this additional tilt distortion coincides with the previously observed change of the magnetic properties, from the nearly ferromagnetic state to the antiferromagnetic correlated state.