Effect of chlorine on solid solution formation in ruthenium titanium dioxide coatings

Rutile-type dioxides of titanium and ruthenium form partial solid solutions at temperatures above 1000°C, whereas the miscibility is complete in the temperature range of 350–600°C, when the oxides are coated on titanium or alumina substrates. The present work tends to show that the Ru_xTi_t?xO₂ coatings are metastable solutions wherein the chloride ions are likely to replace the oxide ions on the sublattice O^2? sites. The increase of a and c parameters in the overall composition range are compatible with a Cl/Ru ratio of 2.5 at.% in the rutile lattice. This ratio does not depend upon the titanium content and therefore it is thought that the Cl^? ions are compensated by reduced Ru³⁺ (or Ti³⁺) species. The electrical conductivity retains its metal-like characteristics in the composition range of 30–100% RuO₂, this is accounted for by the existence of RuO π1 bands along (110) directions. The reduced ions in equilibrium with Cl^? would provide additional paths for electron transport along the c-axis, explaining the high values of conductivity in the concentration range of 30–50% RuO₂.