Effect of dissolved oxygen on thermal oxidation in Ta₂O₅/Ta sandwiches

Chemical analysis, structural investigations, and electrical capacitance measurements have been performed on Ta₂O₅/Ta foils annealed at 753K in air for different initial concentration of oxygen in Ta. It was shown that the initial concentration of oxygen in Ta plays a crucial role in formation of thermal nonstoichiometric oxide layer between tantalum and anodic Ta₂O₅, namely only Ta with low initial oxygen content covered with thin Ta₂O₅ layer is resistant to thermal oxidation. The obtained results may explain the degradation of real capacitors made of fine Ta powders.