Thermoelectric Breakthrough: Nickel-Gold Alloys Set New Standard

Researchers from TU Wien have made a significant discovery in thermoelectric materials. They found that nickel-gold alloys show exceptional efficiency in converting heat into electrical energy. This revelation is a departure from conventional beliefs about metals in thermoelectric applications and paves the way for new technological uses. The study includes a diagram illustrating the thermoelectric effect in these alloys, credited to Fabian Garmroudi.

These thermoelectric materials are capable of directly transforming heat into electrical power and vice versa, drawing increasing interest for their technological applications. The TU Wien team investigated various metallic alloys to identify the most effective thermoelectric material.

Nickel and gold, when combined, exhibited particularly notable results. Their findings were published in the prestigious journal, Science Advances.

Thermoelectrics have been utilized since the mid-20th century, particularly in space exploration for generating electrical energy, and in everyday items like portable coolers. Their potential extends to industrial use, where they can turn waste heat into eco-friendly electricity.

Understanding Thermoelectricity

The thermoelectric effect involves charged particles migrating from a warmer to a cooler side of a material, creating an electrical voltage, known as thermoelectric voltage. This opposes the thermal motion of charge carriers.

The Seebeck coefficient, named after German physicist Thomas Johann Seebeck, measures the ratio of thermoelectric voltage to temperature difference. It is crucial for a material’s thermoelectric performance and depends on an imbalance between positive and negative charges.

The team, including Michael Parzer, Fabian Garmroudi, and Andrej Pustogow, displayed against a backdrop of a periodic table indicating the electronic structure of solid elements. Credit: TU Wien.

Fabian Garmroudi, the study’s lead author, notes that despite Seebeck’s discovery of the thermoelectric effect in common metals over two centuries ago, metals are not typically seen as thermoelectric materials due to their generally low Seebeck coefficients. Metals like copper, silver, and gold have high electrical conductivity but usually insignificant Seebeck coefficients.

The Exceptional Traits of Nickel-Gold Alloys

The Institute of Solid State Physics at TU Wien has discovered metallic alloys with both high conductivity and a significantly large Seebeck coefficient. Combining magnetic nickel with noble gold dramatically alters their electronic properties.

When roughly 10% nickel is added to gold, resulting in the loss of gold’s yellowish hue, there is a sharp increase in thermoelectric performance. This is due to the energy-dependent scattering behavior of electrons, a principle distinct from that in semiconductor thermoelectrics.

The periodic table depicted shows the electronic structure of all solid elements. Credit: Fabian Garmroudi, Michael Parzer, Andrej Pustogow.

In these alloys, nickel atoms cause a greater scattering of positive charges compared to negative ones, leading to the desired charge imbalance and high thermoelectric voltage.

Andrej Pustogow, the study’s senior author, likens this to a race where one runner faces a clear path while the other encounters numerous obstacles. In these alloys, positive charges are heavily scattered by nickel electrons, whereas negative charges move with minimal disturbance.

Unprecedented Thermoelectric Material

Nickel-gold alloys exhibit an extraordinary combination of high electrical conductivity and a significant Seebeck coefficient, resulting in thermoelectric power factor values that far surpass those of conventional semiconductors.

Fabian Garmroudi explains that these alloys could generate considerably more electrical power than any other known material under the same conditions. The high power density of these alloys might also facilitate their use in various large-scale applications. Andrej Pustogow suggests that even current performance levels could enable devices like smartwatches to charge autonomously using body heat.

Beyond Nickel-Gold

Michael Parzer, a lead author of the study, emphasizes that while gold is costly, their research is a proof of concept demonstrating that metals, not just semiconductors, can have effective thermoelectric properties suitable for diverse applications. Metallic alloys offer certain advantages over semiconductors, particularly in manufacturing thermoelectric generators.

Their experimental success with nickel-gold alloys as high-performance thermoelectrics was no accident. Preceding the experiments, theoretical models were used to identify the most promising alloys. The team is currently exploring other promising candidates that don’t require gold.

Reference: “High thermoelectric performance in metallic NiAu alloys via interband scattering” by Fabian Garmroudi, Michael Parzer, Alexander Riss, Cédric Bourgès, Sergii Khmelevskyi, Takao Mori, Ernst Bauer and Andrej Pustogow, 15 September 2023, Science Advances. DOI: 10.1126/sciadv.adj1611

Frequently Asked Questions (FAQs) about Thermoelectric Materials

More about Thermoelectric Materials

• Thermoelectric Materials Overview
• TU Wien Research Discoveries
• Nickel-Gold Alloys in Thermoelectrics
• Energy Conversion Technologies
• Advances in Thermoelectric Research
• Seebeck Effect and Its Applications
• Future of Thermoelectric Materials
• Science Advances Journal Publication