Thermal conversion of Cu4O3 into CuO and Cu2O and the electrical properties of magnetron sputtered Cu4O3 thin films

Among the three oxides of copper (CuO, Cu2O, and Cu4O3), Cu4O3 phase (paramelaconite is a natural, and very scarce mineral) is very difficult to synthesize. It contains copper in both +1 and +2 valence states, with an average composition Cu21+Cu22+O3. We have successfully synthesized Cu4O3 phase at room temperature (300 K) by reactive DC magnetron sputtering by controlling the oxygen flow rate (Murali and Subrahmanyam in J Phys D Appl Phys 49:375102, 2016). In the present communication, Cu4O3 thin films are converted to CuO phases by annealing in the air at 680 K and to Cu2O phase when annealed in argon at 720 K; these phase changes are confirmed by temperature-dependent Raman spectroscopy studies. Probably, this is the first report of the conversion of Cu4O3-CuO and Cu2O by thermal annealing. The temperature-dependent (300-200 K) electrical transport properties of Cu4O3 thin films show that the charge transport above 190 K follows Arrhenius-type behavior with activation energy of 0.14 eV. From photo-electron spectroscopy and electrical transport measurements of Cu4O3 thin films, a downward band bending is observed at the surface of the thin film, which shows its p-type semiconducting nature. The successful preparation of phase pure p-type semiconducting Cu4O3 could provide opportunities to further explore its potential applications.