Novel synthesis method of nonstoichiometric Na2-xIrO3. Crystal structure, transport and magnetic properties

TL;DR

This paper reports a new synthesis method for nonstoichiometric Na2-xIrO3, revealing how sodium reduction alters its crystal structure, oxidation state, and physical properties, including magnetic and transport behaviors.

Contribution

It introduces a novel synthesis approach to create nonstoichiometric Na2-xIrO3 and explores the resulting changes in structure and physical properties compared to stoichiometric compounds.

Findings

Sodium reduction changes iridium oxidation state from +IV to +V/+VI.

The compound's symmetry shifts from C2/c to P-3.

Magnetic order vanishes at 15K and transport becomes semiconducting.

Abstract

Transition metal oxides with 4d or 5d metals are of great interest due to the competing interactions, of the Coulomb repulsion and the itineracy of the d-electrons, opening a possibility of building new quantum ground states. Particularly the 5d metal oxides containing Iridium have received significant attention within the last years, due to their unexpected physical properties, caused by a strong spin orbit coupling observed in Ir(IV). A prominent example is the Mott-insulator Sr2IrO4. Another member of this family, the honeycomb lattice compound Na2IrO3, also being a Mott-insulator having, most probably, a Kitaev spin liquid ground state. By deintercalating sodium from Na2IrO3, we were able to synthesize a new honeycomb lattice compound with more than 50% reduced sodium content. The reduction of the sodium content in this layered compound leads to a change of the oxidation state of iridium from +IV to +V/+VI and a symmetry change from C2/c to P-3. This goes along with significant changes of the physical properties. Besides the vanishing magnetic ordering at 15K, also the transport properties changes and instead insulating semiconducting properties are observed.