| ZrW2O8
has been show to exhibit negative thermal expansion over a wide temperature
range.
This property has been related to the unusual topology of the structure, which exhibits a large number of rigid unit modes. These can be described as vibrations in which the constituent ZrO6 octahedra and WO4 tetrahedra of ZrW2O8 are undistorted. Many of these modes have a negative Gruneisen parameter and thus tend to cause a contraction of the structure when populated. These are low energy modes and thus remain populated even at very low temperatures. Physical measurements by Ramirez and co-workers support this basic model. Much of our work on ZrW2O8 has been performed in collaboration with Art Sleight of Oregon State University. |
Animations showing the potential structural flexibility of ZrW2O8:
