Some organic crystals jump around when heated up because of an extremely fast change in their crystal structure. Scientists have now demonstrated that the crystals also send out acoustic signals during this process, a popping sound.

Researchers from NYU Abu Dhabi, the German Electron Synchrotron in Hamburg, and the Max Planck Institute for Solid State Research in Stuttgart started from the assumption that the sudden release of the accumulated elastic tension in jumping crystals results in relatively strong acoustic waves, similar to seismic waves from an earthquake.

Led by Panče Naumov, NYUAD associate professor of chemistry, they decided to study crystals of the amino acid derivative L-pyroglutamic acid, which change their crystal structure when heated to between 65 and 67 degrees Celsius and return to their starting structure when cooled to between 55.6 and 53.8 Celsius.

As expected, the crystals give off clear acoustic signals during the transition from heat to cool. However, the scientists also determined, unexpectedly, that the two different crystal structures they examined are very much alike, which was unexpected given the impressive crystal motility.

The results indicate that organic matter, which is normally perceived as soft and brittle, and much harder materials, such as metals and metal alloys are, at least at the molecular level, not that different, Naumov said, “which could be of tremendous significance for applications such as all-organic electronics.”

“Research into organic solid states could allow us to gain a better understanding of the related macroscopic effects,” Naumov and the research team concluded.