Amorphous, anodically grown tantalum pentoxide serves as a dielectric layer in capacitors using anodes constructed from tantalum. These capacitors are extensively used in demanding high-reliability applications such as military, aerospace and medical systems. One of the degradation mechanisms in this oxide layer is crystallization induced by applied electric fields. Previous studies have described many attributes of this process. However, the role of stress and strain in the crystallization process has not been explicitly studied to date. The purpose of the present study is to directly monitor the stress evolution and understand its role in the field-induced crystallization of anodic tantalum oxide (ATO). To this end, tantalum was deposited onto quartz substrates by electron beam evaporation and subsequently anodized in acidic electrolytes. A multi-beam optical technique was then used for the in situ measurement of stress evolution in the anodic thin films during the application of electric fields whose strengths are on the order of 5.5 x 10(6) V/cm. The salient features of field-driven crystallization in acidic electrolytes were additionally tracked using microscopy. The results indicate that field-induced crystallization of ATO is associated with compressive stresses. The methods used in the present study offer a promising new approach for a detailed mechanistic understanding of the stresses associated with the field crystallization process in ATO. (c) 2012 Elsevier Ltd. All rights reserved.