Thermo-physical properties of thin films composed of anatase TiO2 nanofibers

In this paper, anatase titanium dioxide (TiO2) thin films similar to 60 pm thick are fabricated using the electrospinning technique. The prepared thin films are composed of interconnected anatase TiO2 nanofibers. The transient electro-thermal technique, combined with a temperature-resistance calibration procedure, provides a full spectrum study which examines the relationship between the film's thermal diffusivity, density and thermal conductivity. It is found that the annealing process significantly reduces the thermal diffusivity of the sample from 3.73 x 10(-5) m(2) s(-1) to the order of 10(-6) m(2) s(-1). The effective thermal diffusivity, conductivity and density of the films are 1.35-3.52 x 10(-6) m(2) s(-1), 0.06-0.36 W m(-1) K-1 and 25.8-373 kg m(-3), respectively. These values are about one order of magnitude or more lower than the bulk property values. This difference is attributed to the loose interior structure and large concentration of vacancies. A microscale physical model is designed to explore the intrinsic thermal conductivity of the discrete TiO2 nanofibers that compose the films. The calculated intrinsic thermal conductivity of the TiO2 nanofibers varies from 4.67 to 12.2W m(-1) K-1, which is comparable with the bulk thermal conductivity of 8.5W m(-1) K-1. The phonon mean free path calculation demonstrates that the nanofiber size has a negligible impact on the phonon transport. The major restriction on the heat transfer originates from the crystalline structure defect. (c) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.