Mamoru Senna

Keio University, Yokohama, Japan Faculty of Science and Technology, Hiyoshi, Yokohama 223-8522, Japan

Oxygen deficient oxide materials, including less stable oxides of lower oxidation number, are of great technological significance. They are conventionally prepared from stable oxides by heating under reducing atmosphere. Opposite processes, i.e. from metals by sparingly oxidizing under controlled oxygen partial pressure are less popular but some attempts were also made. Abstraction of lattice oxygen from stable oxides, mostly with highest oxidation number, is not just a simple reduction. Mechanisms of such phenomena are well documented in the interests of semiconductor technology and catalytic activity. However, such accumulated knowledges are not always taken over for the preparative methods of modern functional materials. When electrophilic species are coexisting and participate in such a preparative process, abstraction of lattice oxygen creates oxygen vacancies, leading to subsequent reduction of the oxides. The same principle is directly extended to the anion exchange, e.g. toward oxyhalides when an electrophilic materials we use contain halogens. The presentation is based on the related recent studies carried out by the author and his colleagues on V₂O₅, TiO₂, SiO₂ and SnO₂. Some new insights why and how are those less stable oxides exhibit their functionalities are discussed in view of their application to energy storage devices, among others thermal energy storage via latent heat during phase change, and Li-ion battery anode is briefly referred.

Keywords

Oxygen deficient oxides, Oxygen abstraction, Electrophilic species, Oxygen deficient oxides, Energy storage materials