[show abstract][hide abstract] ABSTRACT: The phase diagram of Ca2-xSrxRuO4 has been studied by neutron diffraction on powder and single-crystalline samples. The experiments reveal antiferromagnetic order and structural distortions characterized by tilts and rotations of the RuO6 octahedra. There is strong evidence that the structural details of the isovalent samples tune the magnetic as well as the electronic behavior. In particular we observe for low Sr concentration a metal-insulator transition associated with a structural change and magnetic ordering.
[show abstract][hide abstract] ABSTRACT: The crystal and magnetic structure of Ca2RuO4 (CRO) has been studied by powder neutron diffraction. CRO was synthesized in two different modifications (stoichiometric and containing excess oxygen) whose crystal structures are, in spite of strong differences in the lattice constants, closely related. Both structures are derived from the ideal K2NiF4 structure type by a rotation of the RuO6 octahedra around the long axis, combined with a tilt around an axis lying in the RuO2 plane. The orientation of the tilt axis seems to distinguish the two room-temperature symmetries; the excess oygen compound is characterized by a smaller tilt angle and shorter Ru-O in-plane bond distances. Stoichiometric CRO undergoes large structural changes on cooling, though no symmetry change was detected. In contrast, the excess oxygen containing compound undergoes a first-order structural phase transition accompanied by a change from metallic to insulating behavior in the electric resistivity. Both compounds exhibit antiferromagnetic order below 110–150 K; for the stoichiometric sample, the onset of magnetic order is associated with several structural anomalies.