Structural stability of titania thin films

This paper studies the stability of thin films 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 structure of the films consists of nanocrystalline anatase (∼8nm). Exposure of the films to temperatures > 400°C results in the nucleation and subsequent rapid growth of rutile grains (final grain size > 300nm). In-situ, hot-stage experiments in the TEM were carried out, which revealed details about the nucleation and abnormal grain growth processes in this 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 process for maintaining nanosize grains in the transformed material.