Materials exhibiting novel electronic ground states (i.e. not explained by the typical models used for metals, insulators, and semiconductors) are of interest due to the emergence of functional properties not observed in traditional materials. Besides superconductivity and magnetic order, such correlated oxide materials host a vast landscape of unexplored physics, with applications in various industries from energy storage and lighting to low-power computing. Correlated iridate oxides are of interest due to the novel topological behavior caused by electron-electron- as well as spin-orbit interactions, which can be finely tuned by stoichiometry.
Pyrochlore iridate samples were grown by grinding, pelletizing, and annealing reagent powders. Full Rietveld refinement of powder x-ray diffraction patterns allowed for accurate measurement of phase content in order to evaluate Nd2 Ir2O7 yield and detect unwanted phases including Nd3IrO7 and reagent powders. By optimizing growth parameters, phase purity was improved from 10% to better than 90%. Using samples of at least 80% purity, the flux growth technique was used to produce octahedral crystals about 0.4 mm long.
Resistivity measurements confirm the emergence of a metal-insulator transition around 33K. SQUID measurements show a divergence between FC and ZFC at a particular onset temperature, however this temperature varied between powder and single-crystal experiments. Magnetization measurements will be used to further characterize this Mott-insulator to metal phase transition, and to investigate the Dirac-semimetal phase expected to emerge near this point in the topological phase diagram. In addition, single crystal XRD will be used to more precisely determine phase purity and occupation parameters.