Gregory V. Taylor^1,2, Theodore Scabarozi¹, Samuel Lofland¹, Jeffrey Hettinger^1
1Rowan University, Glassboro NJ
²Lawrence Livermore National Laboratory, Livermore, CA
Coatings added to implantable electrodes based on electrochemical methods improve performance of the electrodes. Recent work has shown that the charge exchange performance of reactively sputtered Platinum Group Metal (PGM) oxide films is improved when deposited at high oxygen partial pressures (OPP) and high working pressures (WP). Significant evidence suggests that this is the result of increased porosity of the resulting coatings deposited under these conditions. Due to the nearly amorphous nature of most of the high performing PGM-oxide coatings, detailed crystallographic analysis is generally not practical. However, palladium oxide (PdO) is an exception, demonstrating relatively strong x-ray diffraction (XRD) peaks. Despite these differences in crystallinity, the microstructures observed and the electrochemical performance of PdO demonstrate trends like those of the other PGM oxides. Reactive magnetron sputtered PdO films have been synthesized at various OPP and WP. The availability of oxygen and the impact of the chamber pressure has resulted in varying densities and porosities of the coatings and has resulted in improved electrochemical performance as measured by cyclic voltammetry. In this presentation, systematic results that indicate the existence of nonequilibrium palladium oxide polymorphs are presented. The evidence suggests that the x-ray diffraction peak breadth is a result of a continuous distribution in lattice parameter. This results from a distribution of oxygen contents controlled by the availability of oxygen during deposition as well as the time available before quenching when incident on the substrate. The instability of the polymorphs is confirmed through in-situ x-ray diffraction measurements during low-temperature annealing.