Crystal Growth of Cu₂O Consisting of Sequential mm Size Grains by Thermal Oxidation of Cu

Cu ₂O has been grown via the thermal oxidation of 2 mm × 20 mm, 45 μm thick Cu under Ar: O₂ at 1020 °C, followed by annealing at 1100 °C and controlled cooldown at -5 °C/min under Ar. We obtain Cu ₂O consisting of millimeter-size sequential grains that have a cubic crystal structure and exhibit minimal bending and bowing, which allows the removal of the Kirkendall voids that form in the middle of the bulk due to the bifacial oxidation, by postgrowth polishing. We describe in detail this growth and processing strategy, which employs a considerably lower thermal budget compared to optical float zone growth, and show in contradistinction that the thermal oxidation of Cu wires using the same growth conditions leads to the formation of Cu ₂O containing a significantly larger density of Kirkendall voids compared to the planar case that cannot be removed by annealing or polishing. We discuss the impact of these voids existing in feed and seed rods employed for the growth of Cu ₂O by the optical float zone method and suggest that the growth strategy described here is an important alternative toward the realization of high crystal quality Cu ₂O.