Optical properties of crystalline tungsten oxide

When designing a thermal control device based upon crystalline tungsten oxide it is vital to have knowledge of both n, the real part of the refractive index and k, the complex part. With this knowledge it is possible to predict the performance of an electrochromic device at different wavelengths of radiation. We performed a series of experiments on crystalline samples of tungsten oxide where both n and k were carefully determined from spectral reflectance and transmittance measurements after set amounts of charge were inserted electrochemically, thus reducing the tungsten oxide. The trends for n and k are different, which has implications for device performance and design. We also investigated the effect of deposition temperature on the optical properties of crystalline tungsten oxide. This has implications for both the substrate that may be used in a device and the construction of the device. The final data we shall present are some electrochemical studies of insertion into crystalline tungsten oxide flake samples and powder samples. The flakes and powder are deposited in a similar way to graphite "paste" electrodes used in Li ion battery studies. This is a possible route to a flexible electrochromic device based upon crystalline tungsten oxide.