We report structural studies of the spin-orbit Mott insulator family ${\mathrm{K}}_x{\mathrm{Ir}}_y{\mathrm{O}}_2$, with triangular layers of edge-sharing ${\mathrm{IrO}}_6$ octahedra bonded by potassium ions. The potassium content acts as a chemical tuning parameter to control the amount of charge in the Ir-O layers. Unlike the isostructural families with Ir replaced by Co or Rh ($y=1$), which are metallic over a range of potassium compositions $x$, we instead find insulating behavior with charge neutrality achieved via iridium vacancies, which order in a honeycomb supercell above a critical composition $x_c$. By performing density functional theory calculations we attribute the observed behavior to a subtle interplay of crystal-field environment, local electronic correlations, and strong spin-orbit interaction at the ${\mathrm{Ir}}^{4+}$ sites, making this structural family a candidate to display Kitaev magnetism in the experimentally unexplored regime that interpolates between triangular and honeycomb structures.

• Received 13 August 2019

DOI:https://doi.org/10.1103/PhysRevB.100.214113