On January 26, 2026, researchers at the Tokyo University of Science (TUS), Japan, announced a breakthrough: the discovery of a new class of mixed-dimensional semimetal, molybdenum disilicide (MoSi₂). This single material could transform waste heat into usable energy, opening new possibilities for sustainable power generation.
The Thermodynamics of Waste Heat
The art of thermoelectric conversion devices offers a unique solution by directly transforming a temperature gradient into electrical potential without the use of moving parts, working fluids, or greenhouse gas emissions, aligning with researchers’ missions. Associate Professor Ryuji Okazaki from the Tokyo University of Science team, along with Hikari Manako, Shoya Ohsumi, Shogo Yoshida, and Assistant Professor Yoshiki J. Sato from Saitama University, published their findings. Their discovery identified the mixed-dimensional semimetal molybdenum disilicide as a premier material for TTE applications.
Transverse thermoelectric (TTE) devices generate a voltage perpendicular to the direction of heat flow. This orthogonal relationship allows for the creation of a conversion device from a single piece of material. To produce usable power, these modules consist of alternating layers of p-type and n-type semiconductor elements connected electrically in series and thermally in parallel.
Discovery of Molybdenum Disilicide MoSi₂
The Tokyo University of Science (TUS) is the largest science-specialized institute in Japan and has been home to Nobel Prize winners. The lead researcher, Dr. Ryuji Okazaki, is an expert in correlated electron systems and condensed matter physics, with over 150 published articles.
Due to its unique electronic structure and axis-dependent conduction polarity, it emerges as a potential thermoelectric material. MoSi₂ has been used in industrial high-temperature applications as a heating element because of its refractory nature and excellent oxidation resistance. The team explored its transport properties using a combination of experimental measurements and first-principles calculations.
“Our objective was to investigate emerging transverse thermoelectric (TTE) materials,” explains Dr. Okazaki. “The recent identification of axis-dependent conduction polarity (ADCP) within certain materials has opened new possibilities, as it signals strong potential for TTE generation. Mixed-metal conductors such as MoSi₂ have long been considered promising ADCP candidates; however, their thermopower generation capabilities remain largely underexplored.”
The Mechanism of Axis-Dependent Conduction Polarity (ADCP)
The key to MoSi₂’s performance is its axis-dependent conduction polarity. Known as a goniopolar material, the dominant carrier type changes depending on the crystallographic direction. The origin of ADCP in MoSi₂ lies in its complex Fermi surface. The calculations performed by the team revealed that mixed-dimensional electronic surfaces occupy different spatial dimensions:
Quasi-One-Dimensional (1D) Electron Surfaces: These surfaces are associated with electron-like carriers that conduct primarily along the cross-plane direction.
Quasi-Two-Dimensional (2D) Hole Surfaces: These surfaces correspond to hole-like carriers that conduct primarily within the in-plane direction.
Stability and Longevity
Comparison of the density of states (DOS) between MoSi₂ and WSi₂. Transverse thermoelectric (TTE) materials can be fabricated as thin or flexible sheets. They can be used for large-area coverage, such as along industrial furnace walls, converting heat into electricity continuously across the surface. Thin, flexible insulating substrates can also be used to wrap modules around exhaust pipes. This portability and structural adaptability make TTE devices ideal for power generation and remote IoT sensors.
The shift toward sustainable energy is being slowed by a fundamental thermodynamic challenge: a significant amount of energy is lost as waste heat. Across industries, power plants, and transportation systems, substantial energy is dissipated. In industrial sectors, this loss creates both economic and environmental challenges, further intensifying the impacts of global warming.
Photo Credits: © Hikari Manako, Shoya Ohsumi, Shogo Yoshida & Ryuji Okazaki
