Indian-led team shatters century-old ceiling on heat-to-electricity conversion
Scientists at JNCASR, with IISc and University of Sydney, have broken a 100-year-old limit on thermoelectric voltage in solids using doped scandium nitride crystals.
Researchers from the Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), in collaboration with the Indian Institute of Science (IISc) and the University of Sydney, have demonstrated a crystalline material that produces an electric voltage from a temperature difference at levels nearly a thousand times greater than previously thought possible for solids.
The discovery overturns a long-standing assumption about the Seebeck effect, a phenomenon discovered two centuries ago in which heating one end of a material and cooling the other causes charge carriers to drift, generating a voltage. This effect is the basis for thermocouples and thermoelectric generators that convert waste heat into electricity.
For decades, the Seebeck coefficient in crystalline solids was believed to be capped at a few millivolts per Kelvin. Most metals produce only tens of microvolts per Kelvin, and even high-performing semiconductors rarely exceed a few hundred microvolts per Kelvin. Only liquid systems such as ionic gels and electrolytes, which rely on charged ions rather than electrons, were known to cross into the millivolt-per-Kelvin range.
The team, led by Bivas Saha at JNCASR, grew thin films of scandium nitride (ScN) on magnesium oxide substrates using ultrahigh-vacuum magnetron sputtering. By deliberately doping the films with magnesium, they compensated for the material's naturally occurring free electrons, creating a heavily doped, highly compensated semiconductor with nearly equal numbers of positive and negative dopant atoms scattered randomly through the crystal.
X-ray diffraction and atomic-resolution electron microscopy confirmed that the films remained single-crystalline and epitaxial, with dopants distributed uniformly and no secondary phases or precipitates. The thermoelectric voltage generated was so large that it rivals values normally seen only in liquid electrolytes and ionic gels.
The breakthrough opens a path to a new generation of ultrasensitive temperature sensors, heat detectors, and quantum sensing devices.