Two copper-molybdenum bronzes: CuyMoO(3-z), (0.1 < y < 0.2; typically y similar to 0.15) and CuxMoO3 (0.2 < x < 0.25; typically x similar to 0.23) were prepared as glistening black polycrystalline materials by the solid state reaction of Cu and MoO3 at 600 degrees C under argon in Pt crucibles. Powder XRD showed that the material with global composition '0.1Cu center dot MoO3' comprises similar to Cu0.15MoO3 and MoO3; whilst '0.2Cu center dot MoO3' comprises similar to Cu0.15MoO3 and similar to Cu0.23MoO3. DTA performed on '0.2Cu center dot MoO3' reveals a reversible solid state phase transition similar to 520 degrees C under argon. Reacting equimolar amounts of Cu2O and MoO2 at 600 C in a Cu crucible under argon yields: Cu6Mo5O18, Cu and MoO2. A tentative subsolidus Cu-MoO2-O isothermal (similar to 25 degrees C) phase diagram under argon is drawn from these data. Oxidation states of Cu and Mo within this system are discussed. (C) 2010 Elsevier Ltd. All rights reserved.