Sputter-deposition and characterization of paramelaconite

While processing techniques for deposition of CuOx/Al multilayer foils were being developed, a method for synthesizing paramelaconite (Cu₄O₃) was serendipitously discovered. These paramelaconite films were successfully synthesized by sputter-deposition from a CuO target. Milligram quantities of uncontaminated material were produced enabling new studies of the morphology, stoichiometry, and thermodynamics of this unique copper oxide. At moderate temperatures, equiaxed paramelaconite grains deposited with a strong out-of-plane texture; at lower temperatures the paramelaconite grains showed no texture but were columnar in geometry. X-ray photoelectron spectroscopy showed that the as-deposited Cu₄O₃had a nonstoichiometric Cu:O ratio of 1.7:1; the ratio of Cu⁺to Cu²⁺was 1.8:1. On heating, this phase decomposed into CuO and Cu₂O at temperatures ranging from 400 to 530 °C. Using differential scanning calorimetry, the heat of formation and Gibbs free energy for Cu₄O₃were estimated to be −453 and −279 kJ/mol, respectively. On the basis of these calculations and our observations, we confirmed that Cu₄O₃is a metastable phase.