Structural stability of titania thin films

This paper studies the stability of thin firms of nanostructured titania at elevated temperatures. Thin films of titania are intended for use in many applications, including high-temperature gas sensing devices. The initial s tructure of the films consists of nanocrystalline anatase (similar to 8nm). Exposure of the films to temperatures > 400 degrees C results in the nucle ation and subsequent rapid growth of rutile grains (final grain size > 300n m). In-situ, hot-stage experiments in the TEM were carried out, which revea led details about the nucleation and abnormal grain growth processes in thi s system. It is argued that coarsening of the nano-structure following the transformation is a characteristic of polymorphic reactions from metastable to stable phases. The nucleation process is a critical rate-controlling pr ocess for maintaining nanosize grains in the transformed material. (C) 2000 Acta Metallurgica Inc.