Researchers in the US have developed a high-temperature material that is 60% better at converting heat to electricity than comparable thermoelectric materials.

Thermoelectric materials

Thermoelectric generators produce electricity from heat due to electrical effect that occurs at junctions between different metals when one junction is hot and the other is cold. As materials that can convert heat directly into electricity, thermoelectrics sound highly promising to reduce global energy consumption. To be of practical use a thermoelectric material must be good at conducting electricity but poor at conducting heat. It must also have a large thermo power, which is the ratio of the voltage to temperature difference across a material to its temperature difference expressed in terms of ZT.

Nanocomposite

One promising group of thermoelectric materials contain robust alloys of several metallic elements, but they suffer from relatively high thermal conductivities. One way of reducing their conductivity is by doping a fine powder of the material to form a nanocomposite containing many tiny grains thereby reducing the overall thermal conduction of the nanocomposite.

Product

A cast ingot of Zr0.5Hf0.5CoSb0.8Sn0.2 is crushed to make a powder with a particle size between 5 and 10 nm. Heat and pressure are then applied to press the powder to get millimetre-sized bars and discs of average grain size of 100 to 200 nm. This is done very carefully to minimize the number of nanoparticles that fuse together to create much larger grains in the finished product.

Properties

Thermo power of the nanocomposite along with its electrical and thermal conductivities is about 60% higher than the best available values. This increase is due probably caused by the preferential scattering of lower-energy charge carriers at grain boundaries, which increases the mean carrier energy in the material. It has excellent thermal stability and good mechanical strength and is non-toxic and inexpensive.

Applications

This nanocomposite material in addition to possibly finding their way into cars, they could also be used to recover useful energy from waste heat from nuclear reactors, improve the effectiveness of solar cells, cooling computer chips and other electronic devices and in power generation. It can also be used to generate electricity from heat of the Sun.