“Scientists, including researchers from DESY, have been fascinated by thermosalient crystals for some time: when placed on a hotplate, these inconspicuous crystals suddenly propel themselves upwards, leaping to heights several times their own length. This abrupt movement is caused by a change in the structure of the crystals. A detailed examination of this transition is very difficult because it is so rapid. Now, scientists have resorted to a new technique and discovered that immediately before altering their structure the crystals emit a sound wave, the analysis of which reveals further details about this exciting phase transition. On top of this, the researchers studied the change in the crystal structure very carefully at DESY. The international team of research scientists, headed by Panče Naumov from the New York University Abu Dhabi of the United Arab Emirates, have reported their findings in the journal Angewandte Chemie International Edition. Like all crystals, thermosalient crystals are made up of a regular array of molecules. When the crystals are heated above a certain temperature (or cooled below it), their structure changes, scientists call this a phase transition. Although the position of the molecules only shifts very slightly, this happens extremely quickly. “Starting from the origin of the transition, the new phase spreads through the crystal almost like a shock wave,” explains DESY scientist Martin Etter, one of the co-authors of the paper. “This shock wave causes the crystal to move by itself and even to jump.” The energy stored while heating the crystal is released all at once.”
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