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Until now, the structural analysis of WO3 films has been insufficient. The similar peak positions of the possible crystalline phases make a precise differentiation difficult or even impossible. In particular, the presence of possible mixed phases is difficult to determine. However, the exact determination of the crystalline phases would be important for use as a photocatalyst, as these phases and also their mixtures may have an effect on the photocatalytic properties. The identification of the monoclinic (P21/n), orthorhombic (Pbcn) and triclinic (P 1¯) components at room temperature seems to be of particular interest. By heating WO3 films before cooling them to room temperature, a broadening of the diffraction peaks was observed, which can be associated with phase transformations. By following these peak broadenings, individual phases of WO3 could be identified and the progression of mixed phases could be visualized. By avoiding a delamination process, which can occur at high temperatures, and an adapted heating strategy, it should be possible to identify different crystalline phases of WO3 films at room temperature after calcination.
Brüger et al. (Tue,) studied this question.