In our previous papers on Electro-Chromic (EC) materials, we have shown that standard inorganic EC structures in the form of EC film/electrolyte/Ion storage films (such as WO3/LiNbO3/NiO), in addition to possessing reconfigurable optical properties also exhibit a degree of electric field induce dielectric tunability at radio frequencies. The extent of dielectric tunability in those standard EC structures is commensurate with the tunability exhibited by more mature bulk-tuneable technologies, such as Liquid Crystals (LCs), being between 5% and 20% depending on the frequency of operation, the thickness of the individual EC layers (EC films, electrolyte and ion tank).
The purpose of this paper is to provide a research review of Electro-Chromic (EC) materials. The review presented in this paper centres primarily on inorganic, type III EC materials, with a complimentary WO3/LiNbO3/NiO, EC cell structure, as elaborated in [1-2]. It summarises the fabrication details, dielectric tunability and possible application domains of EC materials. These first results, despite the fact that the research in this area is in infancy, indicate that the performance of the presented EC materials is on-par with some of the better established bulk-tuneable technologies, such as Liquid Crystals (LC) – K-15 for example.
This new research area is of great potential. Unlike the standard LC technologies, where the tunability is strongly dependent on the size and inertia of the LC molecules, EC materials are composite and consist of at least three active layers. By an appropriate choice of the chemical composition of these layers and appropriate thicknesses, it is believed that both the dielectric tunability can be increased, while reducing insertion losses.
 Bulja, S. et al. High Frequency Dielectric Characteristics of Electrochromic, WO3 and NiO Films with LiNbO3 Electrolyte. Sci. Rep. 6, 28839; doi: 10.1038/srep28839 (2016).
 Bulja, S. et al. High Frequency Dielectric Characteristics of Electrochromic, WO3 and NiO Films with LiNbO3 Electrolyte. Sci. Rep. 7, 13484; doi: 10.1038/s41598-017-13941-9 (2017).