An international team of physicists¹ has developed a method for taking ultrafast "sonograms（声波图） " that can track the structural² changes that take place within solid materials in trillionth-of-a-second intervals³ as they go through an important physical process called a phase transition. Common phase transitions include the melting of candle wax before it burns and dissolving sugar in water. They are purely⁴ structural changes that produce dramatic changes in a material's physical properties and they play a critical role both in nature and in industrial processes ranging from steel making to chip fabrication（制造，装配） .

The researchers have applied⁵ this method to shed new light on the manner in which vanadium（钒） dioxide, the material that undergoes the fastest phase transition known, shifts between its transparent⁶ and reflective phases.

Many of these transitions, like that in vanadium dioxide, take place so rapidly that scientists have had difficulty catching⁷ them in the act. "This means that there is a lot that we still don't know about the dynamics⁸ of these critical processes," said Professor of Physics Richard Haglund, who directed the team of Vanderbilt researchers who were involved.

To build a more complete picture of this phenomenon in vanadium dioxide (VO2), one of the most unusual phase-change materials known, Vanderbilt researchers collaborated⁹ with physicists at the Fritz Haber Institute of the Max Planck Society in Berlin, who have developed the powerful new technique for obtaining a more complete picture of ultrafast phase changes. Details of the method, which can track the structural changes that take place within materials at intervals of less than a trillionth of a second, are reported in the Mar¹⁰. 6 issue of the journal Nature Communications.