Iridate Li 8 IrO 6 : An Antiferromagnetic Insulator.

A polycrystalline iridate Li ₈ IrO ₆ material was prepared via heating Li ₂ O and IrO ₂ 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. Li ₈ IrO ₆ adopts the nonpolar space group R 3̅ with Li atoms occupying the tetrahedral and octahedral sites, which is supported by the electron diffraction and solid-state ⁷ Li NMR. This results in a crystal structure consisting of LiO ₄ tetrahedral layers alternating with mixed IrO ₆ and LiO ₆ octahedral layers along the crystallographic c -axis. The +4 oxidation state of Ir ⁴⁺ was confirmed by near-edge X-ray absorption spectroscopy. An in situ synchrotron X-ray diffraction study of Li ₈ IrO ₆ 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 ( T _N ) of 4 K, which is corroborated by heat capacity measurements. The localized effective moment μ _eff (Ir) = 1.73 μ _B and insulating character indicate that Li ₈ IrO ₆ is a correlated insulator. First-principles calculations support the nonpolar crystal structure and reveal the insulating behavior both in paramagnetic and antiferromagnetic states.