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Materials

Vanadium Dioxide Does A Solid Triple Point

For the first time, researchers find conditions at which three phases of a solid coexist

by Jyllian Kemsley
August 26, 2013 | A version of this story appeared in Volume 91, Issue 34

Phase diagrams show the conditions at which solid, liquid, and gas phases of a material may coexist or occur alone. Phase diagrams can also be drawn for solid-state materials to illustrate the intersections of different electronic, magnetic, or structural phases. By studying temperature- and stress-dependent transitions between metallic and insulating states in vanadium dioxide, a group led by David H. Cobden of the University of Washington, Seattle, has now identified the first triple point for a solid, at which three solid phases co­exist: a coincidence of the metallic and two insulating states of VO2 at 65.0 °C and zero applied stress (Nature 2013, DOI: 10.1038/nature12425). The finding was made possible because the VO2 nanowires used in the study are relatively easy to work with, Cobden says. He notes that the triple point is near room temperature, the material is relatively stable, and his team was able to distinguish the three phases optically. The finding will help researchers understand and exploit the mechanisms of VO2 phase transitions, which are of particular interest for sensing and switching applications. It may also help explain the properties of other materials with metal-insulator transitions, such as high-temperature superconductors.

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