Tuning thermal conductivity of materials 'on the fly'

A team of researchers led by University of Minnesota Twin Cities scientists and engineers have discovered a method for tuning the thermal conductivity of materials to control heat flow ‘on the fly’. The tuning range is reportedly the “highest ever” recorded among one-step processes in the field and could lead to further developments in energy-efficient and durable electronic devices.

Just as electrical conductivity determines how well a material can transport electricity, thermal conductivity describes how well a material can transport heat. For example, many metals used to make frying pans have a high thermal conductivity to transport heat efficiently to cook food. Typically, the thermal conductivity of a material is a constant, unchanging value. However, researchers have now discovered a process to ‘tune’ this value in lanthanum strontium cobaltite, a material used in fuel cells. Similar to the way a switch controls the flow of electricity to a light bulb, the researchers’ method provides a way to turn heat flow on and off in devices.

Xiaojia Wang, co-corresponding author of the study, said that a well-designed and functioning thermal management system would enable better user experience and make devices more durable. “Controlling how well a material can transfer heat is of great importance in daily life and in industry. With this research, we have achieved a record-high tuning of thermal conductivity, showing promise for effective thermal management and energy consumption in the electronic devices people use every day,” Wang said.

Wang’s team worked with University of Minnesota Distinguished McKnight University Professor Chris Leighton, whose lab specialises in materials synthesis. Leighton’s team fabricated the lanthanum strontium cobaltite devices using a process called electrolyte gating, in which ions (molecules with an electrical charge) are driven to the surface of the material. This allowed Wang’s team to manipulate the material by applying a low voltage to it.

Leighton said that electrolyte gating is a powerful technique for controlling the properties of materials and is well established for voltage control of electronic, magnetic and optical behaviour. “This new work applies this approach in the realm of thermal properties, where voltage control of physical behaviour is less explored. Our results establish low-power, continuously tuneable thermal conductivity over an impressive range, opening up some pretty exciting potential device applications,” Leighton said.

Yingying Zhang, first author of the paper, said that while it was challenging to measure the thermal conductivity of lanthanum strontium cobaltite films because they are so ultrathin, it was rewarding when the experiments worked. “This project not only provides a promising example of tuning materials’ thermal conductivity but also demonstrates the powerful approaches we use in our lab to push the experimental limit for challenging measurements,” Zhang said.

The research paper was published in Nature Communications.

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