WASHINGTON, US - BY crushing a widely used semiconductor into nanoparticles, researchers said on Thursday they have created a compound that could lead to cleaner, more efficient refrigerators, solar power plants and other devices.

The crushed material makes it possible to conduct electricity without conducting so much heat, solving a problem that has baffled engineers for 50 years.

Writing in the journal Science, the teams at the Massachusetts Institute of Technology and Boston College said their method provides a cheap way to achieve a major increase in thermoelectric efficiency.

'In order to achieve that 40 per cent less heat conduction you need to have the grains smaller so that you have more blocks to the heat flow.'

Smaller grains of the conducting material - in this case bismuth antimony telluride - scatter and redirect the heat, making a compound that can be used either for cooling or to generate electricity.

'These thermoelectric materials are already used in many applications but this better material can have a bigger impact,' added professor of mechanical engineering at MIT Gang Chen who also worked on the study.

The new material could have applications in solar energy, refrigeration, exhaust systems and even in more prosaic applications.

'You can use this kind of cooling device for the thermoelectric cold car seat in luxury cars,' Professor Ren said.

From picnics to power plants
'You can use it for picnic coolers. A lot of scientific instruments need confined spot cooling,' he said. 'You can also use it for generating electricity. Anywhere you have a heat source like a car exhaust pipe, you can generate electricity from the heat and save gas.'

A joint patent has been issued to Boston College and MIT on the technology and the schools have licensed it to Prof Chen and Prof Ren's start-up company GMZ Energy.

'The nanostructure synthesis method we developed is low cost and can be readily scaled for mass production,' they wrote in their report. 'These results open a cost-effective way to improve the performance of thermoelectric materials.'

The thermoelectric effect, discovered in the early 19th century, involves the direct conversion of temperature differences to electric voltage and back again.

If one end of a device is hotter or colder than the other, the difference can be used to carry electricity.

Thermoelectric materials can be used to control temperatures, but the generation of the effect is inefficient because most materials that conduct electricity also conduct heat, so their temperature equalises quickly.

Scientists have been looking for materials that will conduct electricity but not conduct heat in the same way.

Prof Ren and Prof Chen's team worked with bismuth antimony telluride, a commonly used a semiconductor alloy dating back to the 1950s.

They crushed it into the tiniest particles and then reconstituted it in bulk form with nanoscale constituents. -- REUTERS