High Conductivity in Hydrothermally Grown AgCuO2 Single Crystals Verified Using Focused-Ion-Beam-Deposited Nanocontacts

The silver−copper mixed oxide AgCuO2 (also formulated as Ag2Cu2O4) possesses a peculiar electronic structure in which both Ag and Cu are partially oxidized, with the charge being delocalized among the three elements in the oxide. Accordingly, a quasi-metallic behavior should be expected for this oxide, and indeed bulk transport measurements show conductivity values that are orders of magnitude higher than for other members of this novel oxide family. The presence of silver makes thermal sintering an inadequate method to evaluate true conductivity, and thus such measurements were performed on low density pellets, giving an underestimated value for the conductivity. In the present work we present a new synthetic route for AgCuO2 based on mild hydrothermal reactions that has yielded unprecedented large AgCuO2 single-crystals well over 1 μm in size using temperatures as low as 88 °C. We have used a dual beam instrument to apply nanocontacts to those crystals, allowing the in situ measurement of transport properties of AgCuO2 single crystals. The results show a linear relationship between applied current and measured voltage. The conductivity values obtained are 50 to 300 times higher than those obtained for bulk low density AgCuO2 pellets, thus confirming the high conductivity of this oxide and therefore supporting the delocalized charge observed by spectroscopic techniques.