Effect of IrO2 spatial distribution on the stability and charge distribution of Ti1-xIrxO2 alloys

Rutile structure IrO2 and the related alloy Ti1-xIrxO2 are studied by ab initio simulations. Iridium oxide attracts interest due its exotic metal-insulator transition which may have important applications. In addition, its alloy with TiO2 exhibits reasonable optical transparency, a large work function, high electronic conductivity, corrosion resistance, and excellent properties as a water oxidation catalyst; however, the stability of the alloy with respect to phase separation is not well understood. To study the structure and properties of this metal oxide alloy, a new tool called SCIR (structure classification by image recognition) is developed, allowing the analysis of large sets of local arrangements of iridium oxide and titanium oxide in Ti1-xIrxO2 alloys by image recognition techniques. This study demonstrates that applying hydrostatic pressure to bulk IrO2 can modify its local charge distribution, increasing the electronic charge density between Ir and O ions as the pressure increases. Further, it is found that a local aggregation of iridium oxide in Ti1-xIrxO2 in which four Ir-O octahedra columns are connected to form a "pipe" structure parallel to the c-axis of the crystal structure is the most stable arrangement, suggesting a modest propensity for phase separation in this alloy system. This local IrO2 aggregation increases the electronic conductivity of the alloy by creating conductive channels for charge transport.