Randomly aligned defects explain the low thermal conductivity of some materials

QUT researchers have identified why some materials are better able to block heat, a key feature for energy conversion, insulation and gas storage.

The study, published in Nature Communications, discovered a structural mechanism that explains why some compositionally heterogeneous materials exhibit unusually low thermal conductivity. This is an essential property for converting heat into electrical energy.

Lead author Siqi Liu said the findings cast doubt on traditional models that overlook the role of microstructural features.

“People used to think that the low thermal conductivity of heterogeneous materials was simply due to how the different parts were mixed together,” Liu says. “But we found that it’s actually caused by tiny defects called edge dislocations, which scatter heat better when they’re randomly placed.”

The researchers in this study focused on a commonly used thermoelectric alloy (Bi₀.₄Sb₁.₆Te₃) as a model system.

Researchers used advanced electron microscopy and scanning thermal probe techniques to map the composition and thermal properties of bismuth-antimony-telluride compounds at the atomic level.

Liu said the study found that materials with more randomly mixed bismuth- and antimony-rich zones blocked heat more effectively than materials with more ordered structures.

Liu said this is because defects called edge dislocations are scattered in all directions, impeding heat flow.

Team leader Professor Zhi-Gang Chen said the discovery opens new avenues for designing materials with tailored thermal properties.

“Understanding how these dislocations form and align will allow us to better design materials for energy applications,” Professor Chen said. “This structural insight provides new design principles for low thermal conductivity materials beyond traditional defect engineering.”

Liu said the findings could have far-reaching implications for the industry as a whole.

“Whether it’s improving the efficiency of thermoelectric generators or developing better insulation materials, this research provides new tools to control heat flow at the atomic level,” Dr. Liu said.

The QUT research team were all from the QUT Center for Materials Science and included Dr Siqi Liu, Dr Wei-Di Liu, Dr Wanyu Lyu, Dr Yicheng Yue, Dr Han Gao, Dr Meng Li, Dr Xiao-Lei Shi and Professor Zhi-Gang Chen from the QUT School of Chemistry and Physics and the ARC Research Hub in Zero-Emission Power Generation for Carbon Neutrality. James D. Riches is based at QUT’s Central Analytical Research Facility (CARF). Distinguished Professor Dimitri Golberg is affiliated with QUT’s School of Chemistry and Physics.