Effect of annealing temperature on the thermochromic properties of tungsten oxide films

This work is devoted to the study of thermochromic properties of tungsten oxide films deposited on quartz glass substrates by DC reactive magnetron sputtering. A novelty is the study of the influence of vacuum annealing on the dispersion of optical constants. After deposition, the amorphous WO_3–x films had low absorption in the visible wavelength range. As a result of annealing in vacuum at a temperature of 600 °C or more, a broad absorption band appeared in the transmission spectra of the samples with a maximum in the region of 900…920 nm, as a result of which the films acquired a blue color. Thermochromism in WO_3–x films arose due to the formation of a hydrogen-tungsten bronze phase in their amorphous matrix, which acquired an extremum. It has been established that the dispersion of the absorption coefficient of films in the near-IR range is adequately described by the Breit-Wigner distribution. The use of this distribution made it possible to establish that with an increase in the annealing temperature, the degree of change in the absorption index increases nonlinearly, a decrease in the broadening of the spectral line saturates, and the asymptotic value of the dispersion of the refractive index decreases approximately in proportion to the annealing temperature.

Authors: M. O. Ivantsov, V. I. Shapovalov

Direction: Physics

Keywords: reactive magnetron sputtering, thermochromism, tungsten oxide, vacuum annealing

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