The scientists stumbled on a crystalline semiconductor that converts a temperature difference into an electrical voltage nearly a thousand times larger than textbook physics allows.
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Scientists from the Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR) in a collaborative research have reversed a limit which was accepted for over a century on turning heat into electricity.Scientists from the JNCASR, along with the University of Sydney, Australia and the Indian Institute of Science (IISc), stumbled on a crystalline semiconductor that converts a temperature difference into an electrical voltage nearly a thousand times larger than textbook physics allows.“The thermoelectric voltage generated is so large that it rivals values normally seen only in liquid electrolytes and ionic gels, not in solid, particularly single-crystalline materials,” the Department of Science and Technology said.It added that this discovery overturns a decades-old assumption about the ceiling on this effect in solids and opens a path to a new generation of ultrasensitive temperature sensors, heat detectors, and quantum sensing devices.Seebeck effect“When one end of a junction between two dissimilar materials is heated while the other is kept cold, mobile charge carriers drift from the hot side to the cold side, building up a voltage across the junction. This phenomenon, known as the Seebeck effect, was discovered two centuries ago and underlies technologies ranging from temperature sensors to thermoelectric generators that convert waste heat into electricity,” it said.It added that for decades, the magnitude of this voltage, quantified as the Seebeck coefficient, has placed an upper bound of only a few millivolts per Kelvin on this effect in a crystalline solid. Most metals generate just tens of microvolts per Kelvin, and even good semiconductors rarely exceed a few hundred microvolts per Kelvin. “Only liquid systems, such as ionic gels and electrolytes, in which charged ions rather than electrons carry the heat, have been known to cross into the millivolts-per-Kelvin range,” it added.The scientists have shown that this textbook limit can be shattered in a solid, epitaxial crystal.The team led by Bivas Saha, along with Renuka Karanje and Dheemahi Rao and colleagues Diksha Dadhich and Sourav Rudra from JNCASR, Ashalatha Indiradevi Kamalasanan Pillai and Magnus Garbrecht from the University of Sydney and Subroto Mukerjee from IISc, grew thin films of scandium nitride (ScN), a refractory transition-metal nitride, on magnesium oxide substrates using ultrahigh-vacuum magnetron sputtering.They deliberately doped them with magnesium to compensate for the material’s naturally occurring free electrons from oxygen dopants. This produced what is known as a heavily doped, highly compensated (HDHC) semiconductor, a material in which positively and negatively charged dopant atoms are scattered randomly throughout the crystal in nearly equal numbers.“X-ray diffraction and atomic-resolution electron microscopy confirmed that the films remained single-crystalline and epitaxial, with dopant atoms distributed uniformly and no secondary phases or precipitates,” it said. Published - September 02, 2026 08:04 pm IST
