New Honeycomb Iridium (V) Oxides: NaIrO$_3$ and Sr$_3$CaIr$_2$O$_9$

TL;DR

This paper reports the discovery and characterization of two new iridates with honeycomb lattice structures, NaIrO$_3$ and Sr$_3$CaIr$_2$O$_9$, which are nonmagnetic and serve as platforms to study Ir$^{5+}$ oxides.

Contribution

The paper introduces two novel honeycomb iridates with unique structures and nonmagnetic Ir$^{5+}$ states, expanding the understanding of nonmagnetic behavior in iridates.

Findings

NaIrO$_3$ has a planar honeycomb lattice of IrO$_6$ octahedra.

Sr$_3$CaIr$_2$O$_9$ features a buckled honeycomb lattice with corner-sharing octahedra.

Both compounds exhibit negligible magnetic susceptibility, indicating nonmagnetic Ir$^{5+}$ states.

Abstract

We report the structures and physical properties of two new iridates, NaIrO$_3$ and Sr$_3$CaIr$_2$O$_9$, both of which contain continuous two-dimensional honeycomb connectivity. NaIrO3 is produced by room temperature oxidative deintercalation of sodium from Na$_2$IrO$_3$, and contains edge-sharing IrO6 octahedra that form a planar honeycomb lattice. Sr$_3$CaIr$_2$O$_9$, produced via conventional solid-state synthesis, hosts a buckled honeycomb lattice with novel corner-sharing connectivity between IrO6 octahedra. Both of these new compounds are comprised of Ir$^{5+}$ (5$d^4$) and exhibit negligible magnetic susceptibility. They are thus platforms to investigate the origin of the nonmagnetic behavior exhibited by Ir$^{5+}$ oxides, and provide the first examples of a $J$ = 0 state on a honeycomb lattice.