Synthesis, Structure, and Properties of the Layered Oxide Chalcogenides Sr2CuO2Cu2S2 and Sr2CuO2Cu2Se2

The structures of two new oxide chalcogenide phases, Sr 2 CuO 2 Cu 2 S 2 and Sr 2 CuO 2 Cu 2 Se 2 , are reported, both of which contain infinite CuO 2 planes containing Cu 2+ and which have Cu + ions in the sulfide or selenide layers. Powder neutron diffraction measurements show that Sr 2 CuO 2 Cu 2 Se 2 exhibits long-range magnetic ordering with a magnetic structure based on antiferromagnetic interactions between nearest-neighbor Cu 2+ ions, leading to a √2 a × √2 a × 2 c expansion of the nuclear cell. The ordered moment of 0.39(6) μ B on the Cu 2+ ions at 1.7 K is consistent with the value predicted by density functional theory calculations. The compounds are structurally related to the cuprate superconductors and may also be considered as analogues of the parent phases of this class of superconductor such as Sr 2 CuO 2 Cl 2 or La 2 CuO 4 . In the present case, however, the top of the chalcogenide-based valence band is very close to the vacant Cu 2+ 3d states of the conduction band, leading to relatively high measured conductivity.