Iridate LiIrO: An Antiferromagnetic Insulator.

A polycrystalline iridate LiIrO material was prepared via heating LiO and IrO starting materials in a sealed quartz tube at 650 °C for 48 h. The structure was determined from Rietveld refinement of room-temperature powder neutron diffraction data. LiIrO adopts the nonpolar space group 3̅ with Li atoms occupying the tetrahedral and octahedral sites, which is supported by the electron diffraction and solid-state Li NMR. This results in a crystal structure consisting of LiO tetrahedral layers alternating with mixed IrO and LiO octahedral layers along the crystallographic -axis. The +4 oxidation state of Ir was confirmed by near-edge X-ray absorption spectroscopy. An in situ synchrotron X-ray diffraction study of LiIrO indicates that the sample is stable up to 1000 °C and exhibits no structural transitions. Magnetic measurements suggest long-range antiferromagnetic ordering with a Néel temperature () of 4 K, which is corroborated by heat capacity measurements. The localized effective moment μ (Ir) = 1.73 μ and insulating character indicate that LiIrO is a correlated insulator. First-principles calculations support the nonpolar crystal structure and reveal the insulating behavior both in paramagnetic and antiferromagnetic states.