Cubic WO3 stabilized by inclusion of Ti: Applicable in photochromic glazing

• Highly symmetric WO3 phase is favorable for the photochromic devices.
• This is the first report of Ti stabilized cubic WO3 layer.
• This study reveals a modest sol-gel method to influence WO3 symmetry.
• The addition of Ti leads to WO6 ordering: monoclinic – tetragonal – cubic.
• An increase in the symmetry leads to an up-shift in the redox potential.

We report on the development of WO3 layers with increased symmetry induced by the incorporation of titanium into a crystalline WO3 matrix. The atomic ratio between W and Ti was varied stepwise from 100:1 to 100:20 with pure WO3 layers, made using peroxo sol–gel synthesis, as a reference. Layers were then formed by dip-coating from the corresponding sols. IR spectroscopy and XRD analysis of layers and powders heat-treated at 450 °C proved that the presence of titanium ions induces ordering and increases the symmetry of WO6 octahedra in the WO3 crystalline matrix leading to the transformation of the cell symmetry from monoclinic through tetragonal up to the cubic. Cyclic voltammetry confirmed that this increased symmetry leads to an up-shift in redox potential, which favors the coloration of the layers in photochromic devices. According to our knowledge, this is the first report of colorless cubic WO3 layers, which have potential applications in optoelectronic devices and sensors.