Stress generation and annihilation during hydrogen injection into and extraction from anodic WO3 films

The present work is aimed at investigating the stress generation and release during hydrogen injection into and extraction from anodic WO3 films in a 0.1 M H2SO4 solution using a laser beam deflection technique, combined with cyclic voltammetry and potentiostatic current transients, For this purpose the distribution of donor concentration was measured over the anodic oxide film using the electrochemical impedance technique. From the experimental results, it is suggested that the oxygen vacancies are inherently distributed enriched in the 'layer' adjacent to the anodic WO3 film/W metal interface. The attractive interactions operating between hydrogen and trap sites almost completely release the tensile stresses which would be exerted on the area adjacent to the oxygen vacancies in the absence of the attractive interactions. The area next to the oxygen vacancies provides reversible and irreversible trap sites for hydrogen in the anodic WO3 film. It is concluded that major compressive stresses developed during hydrogen injection into the film are attributed to hydrogen positioned at reversibly active sites, while minor compressive stresses are caused by hydrogen injection into reversible and irreversible trap sites. (C) 1999 Elsevier Science Ltd. All rights reserved.