Members

In the 21st century, “mixed-anion compound,” which consists of multiple monoatomic anions such as O2¯, N³¯, F¯, and S²¯, have attracted attention as a new generation of inorganic materials, established a new scientific field. During the exploration of such new materials, we found a budding discovery; that is a group of materials containing molecular anions such as (OH)¯, (O₂)²¯, (SCN)¯, (NCN)²¯, and (BH₄)¯ in ceramics. We named them “supra-ceramics”. The objective of A01 is to establish synthetic methods for the inner-type supra-ceramics, which incorporate molecular ions (anions) in the crystalline lattice, from the viewpoint of solid-state chemistry. We develop special synthetic methods by incorporating molecules into the conventional method for ceramics and provide guidelines for the design and construction of supra-ceramics with new degrees of freedom based on anisotropic shapes and dynamic properties of molecular ions.

The controls of structural dimensionality and crystal morphology are essential to develop new properties and to enhance the functionality of inorganic materials. This is because electronic states and structural properties of the materials are also greatly influenced by macroscopic factors such as surface area, exposed crystal-face, and domain size. To control the structural dimensionality and crystal morphology of supra-ceramics incorporating molecular units, it is essential to precisely control the arrangement of molecules in the crystal structure and during crystal growth. A02 aims to establish a structural design guideline focusing on the structural dimensionality and crystal morphology of supra-ceramics based on coordination chemistry. We construct high-order structures by local structure designs of molecules and molecular assembly techniques. We study the roles of molecules in the supra-ceramics deeply, thereby linking them to innovative functions in collaboration with B and C groups.

By synthesis of inorganic materials incorporating molecular units, supra-ceramics trigger new properties and functions that can be applied to practical materials of devices such as catalysts and batteries. A key point to comprehend the origin of the functional manifestations of the supra-ceramics is accurate identifying of their macroscopic and local structures and dynamic structures such as crystal structures, compositions, morphologies, and chemical states, which are the bases for direct material understanding. By applying a variety of advanced structural analysis methods based on advanced metrology, this research group will play a role in elucidating new chemical states and morphologies of supra-ceramics, which are unexpected in conventional ceramics, and will also contribute to understanding their mechanisms of operation using in-situ measurement techniques. In order to promote this research area without delay, the first priority is to quickly establish the process of structure and chemical state determination. Ultimately, the group will integrate several excellent structural assessment studies with advanced measurement methods, which are the specialty of the researchers in this group. Then, we aim to achieve comprehension of the relationship between macroscopic, local, and dynamical structures and functions of novel materials of supra-ceramics.

For conventional ceramic materials, monoatomic “ionic radii” based on the rigid sphere approximation model have been used as a parameter predicting structure stability. On the other hand, the structure of supra-ceramic materials containing molecular ions such as ((CH₃)₄N)+, (CO₃)²¯, and CN¯ may not be simply explained by the ionic radius. Furthermore, molecular ions have an additional degree of freedom in the “geometrical relative relationship between molecules and crystals (or surfaces),” which is expected to further complicate the governing factors of the stable structure in supra-ceramic materials. Therefore, this research group plans to sequentially determine the peculiar structural diversity and its electronic structure in supra-ceramic materials using first-principles calculations. In particular, the group plans to perform exhaustive first-principles calculations for configuration diversity, search for new phases using genetic algorithms, and theoretical analysis of surface/molecular interactions on the surface of supra-ceramics. In addition, a reliable “compass (guideline)” is indispensable to explore the unexplored field of supra-ceramic materials. Through collaboration between research groups in this research area, we would like to construct a “supra-ceramics database” based on theoretical calculations and experiments, and to conduct highly efficient and predictive material design and material exploration by making full use of Materials Informatics (MI) and Artificial Intelligence (AI).

We will develop physical properties and functions specific to supra-ceramics. In particular, we aim to understand and control phase transition phenomena and mechanical properties of materials, which are clearly distinguished from those of conventional ceramics composed of a single element, using various analytical techniques. For example, we will extend the conventional idea of ceramics as hard and isotropic by developing supra-ceramics that exhibit a melting point below 300 ºC and softness (elasticity) comparable to that of organic polymers. The superior properties of these supra-ceramics are expected in the bulk and at interfaces. Functions such as conductivity, optical properties, and reaction selectivity are linked to the anisotropy and responsiveness of the introduced molecular units, as well as to non-equilibrium phenomena. By manipulating not only the microscale structure design but also the microscale material geometry, we will discover and deepen our understanding of new phenomena such as the rectification of ion transport and superconductivity at the inorganic-organic interface. With these unique operating principles, supra-ceramics can provide new value as new materials for solving energy and environmental problems, such as batteries and catalysts.

Expectations are growing for breakthroughs in the field of materials science to solve the problems of resources, energy, and health. Inorganic materials with molecular units (molecular ions, complexes, clusters, etc.) are known as “supra-ceramics,” and the emergent fusion of inorganic materials and molecular units enables them to perform functions that they would not be able to perform on their own. For example, the hybridization of the solid photocatalyst C₃N₄ and Ru molecular complex enables visible light CO₂ conversion at room temperature and pressure, which could not be achieved by each alone. In addition, transition metal fluorides have been shown to have high battery capacity comparable to existing lithium batteries due to the formation of molecular ion species in the crystals. This research group will collaborate with the synthesis group to construct a material system with the rectification of electron transfer by utilizing the structural anisotropy (hierarchical structure) and chemical diversity of the supra-ceramics derived from molecular components. In collaboration with the C01 group, which is exploring physical properties, we will develop high-performance photocatalysts with suppressed electron-hole recombination, secondary battery materials with the high-speed and high-stability operation, and biofunctional materials with both anti-infective properties and bone regeneration capabilities. We will create innovative functions unique to supra-ceramics containing molecular units, such as highly selective conversion of low concentrations of carbon dioxide, which has not been possible with conventional ceramics. Furthermore, we will analyze the structure-function relationship by evaluating the functions of new materials produced in the area, identify promising materials, and provide guidelines for the design of supra-ceramics for the expression of their functions.