Hydration processes were previously thought to be limited in amorphous tantalum oxide (ATO) capacitors. However, in-situ measurements show that hydration can produce substantial stresses in ATO. These measurements were also used to systematically investigate several important factors during hydration: the ATO thickness, electrolyte pH, annealing, and electrical field variations. Analysis of these data indicates that hydration in aqueous electrolytes is a diffusion limited process with diffusivities of 2-3 (10)(-15) cm(2)/sec. Pulsed electric fields with different strengths were also applied to further elucidate stress contributions from different mechanisms. Heat treatments up to 400 degrees C produce changes in the structure of the ATO that leads to significant variations in the electrochemical hydration behavior. (C) 2013 The Electrochemical Society. All rights reserved.