Thermal Energy Materials Group

In the 20th century mankind has achieved unprecedented control over the electron, spin, photon, however one of the most important scientific challenges for the 21st century is how to achieve a high degree of control over phonons, or rather thermal energy.
Our group is mainly involved in research on development of cutting edge thermoelectric materials and also fundamental understanding, measurement technology, and control over thermal transport. We are also involved in developing thermoelectric devices which can be used to autonomously power innumerable IoT sensors, and modules for realizing energy saving and zero emission.

Specialized Research Field

1. Development of novel thermoelectric materials

For thermoelectric material research, we are developing novel enhancement principles based on phonon engineering, and also Seebeck enhancement, which can respectively, overcome the conventional tradeoffs between the individual thermoelectric properties. For the former, for example, we have discovered that selective phonon scattering from nano-micropores can enable simultaneous high electrical conductivity and low thermal conductivity, leading to discovery of a high performance rare-earth free material. For the latter, we have discovered how to utilize magnetism to enhance thermoelectric properties, and have been pioneering the new field of magnetic semiconductor thermoelectric materials. We have demonstrated new principles to enhance the Seebeck effect, through interaction between magnetic moments and electrical carriers, and also spin fluctuation, for example.
In other approaches, we have also been carrying out research on band engineering, material informatics, nanocomposites to control thermal and electrical properties, inorganic-organic hybrids, utilization of grain boundaries and interfaces, to develop novel high-performance thermoelectric materials.

2. Development of measurement technology for thermal transport, and thermoelectric device development

We have developed an original focused picosecond thermoreflectance apparatus, and have been successfully measuring the cross-plane and in-plane thermal diffusivity of thin films, and evaluation of interface thermal resistance. We have also been able to evaluate the site-selective thermal conductivity of small size crystals, for example. 
To realize thermal energy harvesting for IoT sensors and devices, in addition to bulk thermoelectric power generation modules, we have been developing thin film thermoelectric modules, flexible inorganic-organic hybrid power generating sheets. We are also developing high temperature thermoelectric power generation modules for the topping cycles in power plants, namely applications to save energy.

3. Synthesis of novel inorganic materials and properties development

We have been utilizing the particular network structures (e.g. atomic cluster and 2D atomic nets) and structure-property relations of high temperature ceramic materials such as borides to find new functional materials.
We have also been carrying out multi-faceted research on inorganic materials such as novel oxides, silicides, nitrides, chalcogenides (sulfides, selenides, tellurides).