Structure, Chemistry, and Electromechanical Behavior of Mixed Metal (Ruthenium, Titanium) Oxides
by
Joseph E. Suarez
J. M. Rigsbee
Department of Materials Science and Engineering
Abstract
This study focuses on the structure-chemistry-property relationships of ruthenium-titanium-oxide films deposited onto niobium substrates by reactive ion plating, a plasma assisted physical vapor deposition technique. A range of microanalytical techniques including SEM, TEM, electron microprobe, Auger microprobe, x-ray diffraction, and electron diffraction was used to characterize film microstructure, morphology, and chemistry. Film electrochemical activity was studied via anodic polarization testing. A relationship was shown to exist between oxygen flow rate and source evaporation rates, and resultant film microstructure, chemistry and crystal phases. Solid solutions of ruthenium in TiO2 (rutile) and TiO (cubic) formed at average oxygen flow rates below 95 sccm. Films with a dual phase mixture of RuO2 and TiO2 (rutile) were produced when average oxygen flow rates were equal to or exceeded 95 sccm. The presence of TiO2 (anatase), with TiO2 (rutile) and RuO2, was shown to be related to a lowering of the ruthenium evaporation rate and a corresponding decrease in overall ruthenium (and RuO2) content. Films comprised of 80-90 at.% titanium (20-10 at.% ruthenium) in the form of a dual phase mixture of RuO2 and TiO2 (rutile) exhibited the greatest degree of electrochemical activity of those films fabricated and tested for the study, i.e. they possessed the ability to maintain a stable flow of current with little to no rise in applied potential for extended periods of time. Electrochemical activity was diminished in those ruthenium-titanium-oxide films containing either TiO2 (anatase) with TiO2 (rutile) and RuO2, or ruthenium in solid solution with TiO2 (rutile) or TiO (cubic). There is evidence suggesting the possibility that a TiO2 (rutile)-to-TiO2 (anatase) phase transformation is induced by anodic polarization in films containing both TiO2 (anatase) and TiO2 (rutile). It is also suggested that an amount exceeding 5 at.% ruthenium is required to stabilize the rutile form of TiO2 in films comprised of RuO2 and TiO2. The study shows that a combination of ruthenium depletion and substrate oxidation are mechanisms by which the oxide films on niobium lose their electrochemical activity under anodic polarization.
Download (3 MB)