Iridate Li₈IrO₆: An Antiferromagnetic\nInsulator

Abstract

A polycrystalline\niridate Li₈IrO₆ material\nwas prepared via heating Li₂O and IrO₂ starting\nmaterials in a sealed quartz tube at 650 °C for 48 h. The structure\nwas determined from Rietveld refinement of room-temperature powder\nneutron diffraction data. Li₈IrO₆ adopts the\nnonpolar space group <i>R</i>3̅ with Li atoms occupying\nthe tetrahedral and octahedral sites, which is supported by the electron\ndiffraction and solid-state ⁷Li NMR. This results in a\ncrystal structure consisting of LiO₄ tetrahedral layers\nalternating with mixed IrO₆ and LiO₆ octahedral\nlayers along the crystallographic <i>c</i>-axis. The +4\noxidation state of Ir⁴⁺ was confirmed by near-edge X-ray\nabsorption spectroscopy. An in situ synchrotron X-ray diffraction\nstudy of Li₈IrO₆ indicates that the sample is\nstable up to 1000 °C and exhibits no structural transitions.\nMagnetic measurements suggest long-range antiferromagnetic ordering\nwith a Néel temperature (<i>T</i>_N) of\n4 K, which is corroborated by heat capacity measurements. The localized\neffective moment μ_eff (Ir) = 1.73 μ_B and insulating character indicate that Li₈IrO₆ is a correlated insulator. First-principles calculations support\nthe nonpolar crystal structure and reveal the insulating behavior\nboth in paramagnetic and antiferromagnetic states.