Credit: Image courtesy of Kirill Kovnir, University of California, Davis
Scientists discovered a new cage or “clathrate” crystal structure (left) in which the atoms are each bonded to five or six atoms, more than previously seen in clathrates. These larger cages can hold atoms that can freely move or “rattle,” a feature that reduces the thermal conductivity of the materials. Low thermal conductivity is a vital property of materials that transform waste heat into electricity. Critical to the research is how electrons are distributed between the atoms forming chemical bonds (indicated by the color-coded bands in the right image).