Synthesis of rhombohedral LaCuO3 thin films using the oxidation effect of NaClO solution

LaCuO₃ is one of the most fundamental cuprate perovskite blocks and has a similar structure to the cuprate high-temperature superconductor. Therefore, some consider that a study on LaCuO₃ is one of the clues to clarify the mechanism of cuprate high-temperature superconductivity. However, since the synthesis of bulk LaCuO₃ is difficult due to the need for the high-pressure and high-temperature (HPHT) method, not enough research on LaCuO₃ has been done so far. In this paper, I report the successful synthesis of rhombohedral LaCuO₃ thin films using the oxidation effect of NaClO solution without using the HPHT method. The nanobeam electron diffraction pattern of the cross-section of LaCuO_3-δ thin film oxidized in NaClO solution at 80 °C for 72 hours demonstrates the formation of rhombohedral LaCuO₃. The amount of oxygen defects in the rhombohedral LaCuO₃ thin films has not been measured directly because it is difficult to do so. However, considering the relationship between the amount of oxygen defects and the symmetry of bulk LaCuO_3-δ, these rhombohedral LaCuO₃ thin films are considered to be very close to the stoichiometric composition. The temperature dependence of the resistance of the thin films indicates that rhombohedral LaCuO₃ is an insulator. Considering the previous studies on the first-principles calculation of stoichiometric LaCuO₃ and this study, the rhombohedral LaCuO₃ close to the stoichiometric composition is presumed to be a Mott insulator.