Scientists are defying the century-old limit of converting heat into electricity
Scientists have stumbled upon a crystalline semiconductor that converts a temperature difference into an electrical voltage nearly a thousand times greater than what physics textbooks allow. | Photo credit: Getty Images/iStockphoto
In a joint research, scientists from the Jawaharlal Nehru Center for Advanced Scientific Research (JNCASR) overturned a limit that had been accepted for more than a century when it comes to converting heat into electricity.
Scientists from JNCASR, together with the University of Sydney in Australia and the Indian Institute of Science (IISc), have come across a crystalline semiconductor that converts a temperature difference into an electrical voltage almost a thousand times greater than what physics textbooks allow.
“The generated thermoelectric voltage is so large that it rivals values normally found only in liquid electrolytes and ionic gels, not in solids, especially single-crystal materials,” the Ministry of Science and Technology said.
He added that the discovery overturns a decades-old assumption about the ceiling of this effect in solids and paves the way for a new generation of ultra-sensitive temperature sensors, thermal detectors and quantum sensing devices.
Seebeck effect
“When one end of a junction between two dissimilar materials is heated while the other is kept cool, mobile charge carriers shift from the hot side to the cold side, creating 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,” they said.
He added that for decades, the magnitude of this stress, quantified as the Seebeck coefficient, determined the upper limit of this effect in a crystalline solid to only a few millivolts per Kelvin. Most metals generate only tens of microvolts per Kelvin, and even good semiconductors rarely exceed a few hundred microvolts per Kelvin. “Only liquid systems such as ion gels and electrolytes, in which charged ions rather than electrons carry the heat, are known to go into millivolts per Kelvin,” he added.
Scientists have shown that this textbook limit can be broken in a solid, epitaxial crystal.
A team led by Bivas Saha along with Renuka Karanje and Dheemahi Rao and colleagues Diksha Dadhich and Sourav Rudra of JNCASR, Ashalatha Indiradevi Kamalasanan Pillai and Magnus Garbrecht of the University of Sydney and Subroto Mukerjee of IISc grew thin films of scandium nitride and magnesium nitride on magnesium nitride (SMR). substrates using ultra-high vacuum magnetron sputtering.
They deliberately doped them with magnesium to compensate for the naturally occurring free electrons of the material from the oxygen admixture. This created 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 uniformly distributed dopant atoms and no secondary phases or precipitates,” he said.
Published – 02 Sep 2026 20:04 IST