Sputter-deposition and characterization of paramelaconite
- PDF / 215,722 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 108 Downloads / 237 Views
A.J. Wagner and D.H. Fairbrother Department of Chemistry, Johns Hopkins University, 3400 N. Charles St., Baltimore, Maryland 21218
T.P. Weihs Department of Materials Science and Engineering, Johns Hopkins University, 3400 N. Charles St., Baltimore, Maryland 21218 (Received 15 November 2002; accepted 1 April 2003)
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 Cu4O3 had 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 Cu4O3 were estimated to be –453 and –279 kJ/mol, respectively. On the basis of these calculations and our observations, we confirmed that Cu4O3 is a metastable phase.
I. INTRODUCTION
Paramelaconite is a copper oxide containing copper in both the +1 and +2 valence states, and it has an average 2+ composition of Cu1+ 2 Cu2 O3. Its crystal structure is tetragonal (space group I41/amd) with unit cell dimensions of a ⳱ 5.817 and c ⳱ 9.893 Å.1 Several groups have reported that Cu4O3 decomposes to Cu2O or CuO at high temperatures, but neither a high temperature stability limit nor the heat associated with this transition has been firmly established.2 Furthermore, while the heat of formation (⌬H°ƒ) for Cu4O3 has been predicted with computer simulations,3 it has not been measured experimentally. As a commercial material, paramelaconite has few, if any technological uses, due at least in part to its scarcity in nature and the absence of a suitable laboratory synthesis. Other copper oxides, however, have been used and studied extensively because of their unique magnetic, superconducting, and catalytic properties. As a mixed valence oxide, paramelaconite may prove to have important applications as well. Furthermore, Cu4O3 is an important phase to consider in the highly exothermic thermite reaction with aluminum. J. Mater. Res., Vol. 18, No. 7, Jul 2003
Thermite, or reduction/oxidation reactions, of Cu4O3 and Al can be designed to self-propagate at room temperature in CuOx /Al multilayer foils if the individual layers in the foil are submicron in thickness. The reactions can be ignited in the foils with a small thermal pulse from a spark or match, and the heat released by the mixing reaction is sufficient to propagate the reaction across the foils at velocities
Data Loading...
