Materials design utilizing artificial intelligence would be very important for the near future. How to realize novel and/or high performance using abundant elements is a grand challenge for materials scientists to sustain society…
My research focus is to explore novel electro-active functionality using abundant elements. Concretely, my major concerns are placed on oxide semiconductors, iron-based superconductors and electrides.
We discovered that by engineering nano-structure of materials, we could use conventional elements to synthesize numerous inorganic materials with novel electronic functions that defy traditionally held ideas about elements and compounds, thereby contributing immensely to the advancement of basic science and industry.
I discovered that the electron mobility of a transparent amorphous oxide semiconductor, AgSbOx, had a high mobility comparable to that of the corresponding crystal. Based on this finding, I established a design guideline around this difference, which was due to greater spatial spread of metal atomic orbitals carrying the conduction, and developed numerous transparent amorphous oxide semi conducting materials. TAOS, which was pioneered by my research, went on to become a major field in semiconductor research. Amongst them, In-Ga-Zn-O thin film transistor which has a mobility higher by 10-30 times than that in currently used amorphous Si:H TFT first developed by our group, it offered larger mobility and high transparency, finding practical application in an energy-saving device with little current leakage. It has since begun replacing amorphous silicon in LCDs on devices such as PC monitors and tablet PCs, and is also starting to be implemented in large-sized OLEDs.
I also pioneered a new frontier in the exploration of superconducting materials by discovering that iron-based oxypnictide compounds (such as LaOFeAsO), or so-called iron-based superconductors, become superconducting at high transition temperatures, even though their major component is iron, a typical magnetic element that was thought to be unfavorable for superconductivity. This discovery was chosen as a breakthrough of the year 2008 by the Science Magazine and the paper was the most cited paper published in 2008. Iron-based superconductors have grown to a continent of high Tc superconductors comparable to cuprates.
I also succeeded in controlling carrier concentration over wider range than ever before by substituting oxide ions with hydrides, and went on to discover new superconducting regions, thereby contributing significantly to the basic research on the mechanism of superconductivity. Because iron-based superconductors have a high critical magnetic field and advantageous grain boundary properties, applied research is under way to explore its potential as materials for technologies such as superconducting wires to be used under powerful magnetic field.
Furthermore, I discovered an electride composed of cationic skeletons and anionic electrons by replacing oxide ions inside the cage structure of 12CaO・7Al2O3 (C12A7), a constituent of commercial alumina cement, with electrons. This resulting C12A7 electride is the first electride ever to be stable under normal atmospheric conditions. With high electrical conductivity and a work function as low as alkali metals, this new material has transformed the image of cement. My electride research has attracted attention since demonstrating catalysis of ammonia synthesis under low pressure and temperature by harnessing its unique electronic properties, and has led to the discovery of two-dimensional electrides, a new category material. I am continuing to expand on my research alongside pursuing the possibility of its practical application.
As described, I pioneered new frontiers in materials science through the discovery of unconventional inorganic materials with novel electronic functions using ordinary elements, sparking academic enthusiasm across various fields of basic science, while contributing enormously to industry.
I have 3 dreams in research: to create novel amorphous semiconductor exceeding a-Si:H, to find novel superconductors exceeding high-Tc cuprates and to realize efficient catalyst for ammonia synthesis under mild conditions. Although dream 1 was attained by TAOS represented by IGZO, other 2 objectives are still on the way.
Excitement in material science is to find a new functionality which is useful to resolve the social difficulty. Since materials science is an interdisciplinary subject, understanding condensed matter is critical from both sides of physics and chemistry. Materials design utilizing artificial intelligence would be very important for the near future. How to realize novel and/or high performance using abundant elements is a grand challenge for materials scientists to sustain society.