Designing new mixed-anion compounds
Oxide materials are the basis of various electronic technologies and have been supporting our lives and industries. Because most of oxides can be easily synthesized at high temperatures, many oxides have been discovered so far while the development of new materials and functions is coming to a halt. At the beginning of this century, "mixed-anion compounds" composed of two or more anions (O, F, N, H, etc.) are beginning to attract attention as a new generation of materials. Compared with oxides that contain only O2- as an anion, mixed-anion compounds have a much greater degree of freedom in their composition and coordination, and thus can be expected to control functions and exhibit novel properties that are not possible with oxides. However, because of the high volatility of anions such as F, Cl, N, and H, it is not easy to control the composition and crystal structure of the mixed-anion compounds by simple high-temperature synthesis, as has been used in conventional oxides. In fact, the number of mixed-anion compounds that have been reported so far is very limited compared to the oxides, and there are still large frontier in this research field By combining vacuum synthesis, high pressure synthesis, and low temperature topochemical reactions, I have been studying the synthesis of novel compound anionic compounds and to understand the unique functions of mixed-anion compounds from a broad perspective.
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1. Band engineering of layered oxyhalide photocatalysts
The development of a clean and renewable energy carrier that does not utilize fossil fuels is a great technological challenge. One of the most attractive options is the large-scale utilization of hydrogen (H2) as a recyclable energy carrier. Water splitting reactions using semiconductor photocatalysts have the potential to produce hydrogen directly from water by harvesting inexhaustible sunlight energy. However, they are still far from practical efficiency.
My research focuses on novel oxyhalide photocatalysts with a layered structure. The structure of these oxyhalides can be regarded as a stacking of two-dimensional building blocks, and it is possible to construct new structures as if they were Lego blocks by combining these blocks. By studying the relationship between the layered structure and the band structure, I have established a rational way to control the band structure of layered acid halides.
