Annealing Effects and Insulator-to-Metal Transition in Nb Doped Sr₂IrO₄

The effects of vacuum and oxygen annealing on Sr_2-xNb_xIrO₄ samples have been systematically investigated. The annealing under vacuum leads to an enhanced insulating state of the Sr_2-xNb_xIrO₄ compounds, which could be due to the evaporation of oxygen atoms which breaks the superexchange interaction between Ir and O ions. The annealing under oxygen atmosphere results in substantial straightening of the in-plane Ir–O–Ir bond and rapid depression of the canted antiferromagnetic ordering state. Importantly, the insulator-to-metal transition has been achieved by oxygen annealing of the Sr_2-xNb_xIrO₄ samples, which could be due to the enhanced hybridization of Ir 5d orbitals with the neighboring O 2p orbitals. The present results suggest that the annealing treatment could be an effective way for exploring of novel physical phenomena in Sr₂IrO₄ and related compounds.