Revolutionary Breakthrough: Scientists Discover New Method to Control Heat Flow in Materials: Scientists and engineers from the University of Minnesota Twin Cities have made a groundbreaking discovery in controlling the thermal conductivity of materials. This breakthrough could revolutionize the development of energy-efficient and durable electronic devices. The team’s findings, published in Nature Communications, demonstrate the highest-ever recorded tuning range of thermal conductivity through a one-step process.
To understand the significance of this discovery, it’s important to grasp the concept of thermal conductivity. Similar to how electrical conductivity determines a material’s ability to transport electricity, thermal conductivity refers to its ability to transport heat. For instance, metals commonly used in frying pans have high thermal conductivity, allowing efficient heat transfer for cooking.
Traditionally, the thermal conductivity of a material remains constant and unalterable. However, the University of Minnesota researchers have devised a simple method to tune the thermal conductivity of lanthanum strontium cobaltite, a material frequently employed in fuel cells. Drawing an analogy to a switch controlling the flow of electricity to a light bulb, this innovative technology enables the manipulation of heat flow in devices, effectively turning it on and off.
Xiaojia Wang, an associate professor in the University of Minnesota’s Department of Mechanical Engineering and co-corresponding author of the study, emphasizes the importance of controlling heat transfer in everyday life and various industries. The record-breaking achievement in tuning thermal conductivity holds promise for improving thermal management and energy consumption in electronic devices, ultimately leading to enhanced user experiences and device durability.
The team collaborated with Chris Leighton, a Distinguished McKnight University Professor at the University of Minnesota, whose laboratory specializes in materials synthesis. Using a technique called electrolyte gating, Leighton’s team fabricated lanthanum strontium cobaltite devices. Electrolyte gating involves driving ions (electrically charged molecules) to the material’s surface, allowing Wang and her team to manipulate it by applying low voltage.
Leighton explains that electrolyte gating is a powerful method for controlling material properties, established in the realm of voltage-controlled electronic, magnetic, and optical behavior. The researchers’ work expands the application of this approach to thermal properties, which has been less explored. The results demonstrate the achievement of low-power, continuously adjustable thermal conductivity over an impressive range, paving the way for exciting potential device applications.
Yingying Zhang, the first author of the paper and a mechanical engineering Ph.D. alumnus from the University of Minnesota, expresses the excitement of successfully conducting experiments to measure the thermal conductivity of ultrathin lanthanum strontium cobaltite films. This project not only presents a promising example of tuning a material’s thermal conductivity but also showcases the powerful experimental techniques employed by the team to push the boundaries of challenging measurements.
In parallel with this research, scientists from the NOMAD Laboratory at the Fritz Haber Institute have shed light on microscopic mechanisms that contribute to tailoring materials for heat insulation. This development contributes to ongoing efforts to enhance energy efficiency and sustainability.
Heat transport plays a vital role in various scientific and industrial applications, such as catalysis, turbine technologies, and thermoelectric heat converters that transform waste heat into electricity. In the pursuit of energy conservation and the development of sustainable technologies, materials with high thermal insulation capabilities are essential. These materials help retain and utilize heat that would otherwise go to waste, making the design of highly insulating materials a crucial research objective for enabling more energy-efficient applications.
However, creating effective heat insulators is challenging, despite our understanding of the underlying physical laws for nearly a century. Heat transport in semiconductors and insulators has been explained in terms of the collective oscillation of atoms around their equilibrium positions in the crystal lattice. These oscillations, known as “phonons,” involve a vast number of atoms and cover large lengths and time scales.
In a recent publication in Physical Review B and Physical Review Letters, researchers from the NOMAD Laboratory at the Fritz Haber Institute have advanced computational capabilities to compute thermal conductivities with unprecedented accuracy, without relying on experimental data. They demonstrated that the conventional phonon picture is inadequate for strong heat insulators.
Leveraging large-scale calculations on supercomputers, the researchers investigated over 465 crystalline materials with unmeasured thermal conductivities. Their study not only identified 28 highly effective thermal insulators, with six exhibiting ultra-low thermal conductivities comparable to wood but also shed light on an often-overlooked mechanism for systematically reducing thermal conductivity.
Dr. Florian Knoop, the first author of both publications, explains that they observed the temporary formation of defect structures that significantly influence atomic motion for an extremely short period. While these defects are typically disregarded in thermal-conductivity simulations due to their short-lived and microscopically localized nature, the calculations showed that they indeed result in lower thermal conductivities. Dr. Christian Carbogno, a senior author of the studies, adds that these insights present new opportunities for fine-tuning and designing thermal insulators at the nanoscale level through defect engineering, potentially contributing to advancements in energy-efficient technology.
