As per the study, VO2 has an insulating phase when relaxed at room temperature and undergoes a steep insulator-to-metal transition at 68 °C, where its lattice structure changes.
Under normal conditions, VO2 displays volatile features. “The material reverts to the insulating state right after removing the excitation,” said Mohammad Samizadeh Nikoo.
The discovery was unexpected
During the experiment, Samizadeh Nikoo applied electric current to a sample of VO2. “The current moved across the material, following a path until it exited on the other side,” he said.
After the current passed in the first application, the material returned to its state, and after the second application of Samizadeh Nikoo, the material began to show “remembering” features.
“The VO2 seemed to ‘remember’ the first phase transition and anticipate the next,” explains Prof. Elison Matioli, who heads the POWERlab. “We didn’t expect to see this kind of memory effect, and it has nothing to do with electronic states but rather with the physical structure of the material. It’s a novel discovery: no other material behaves in this way.”
The researchers went on to find that VO2 is capable of remembering its most recent external stimulus for up to three hours.
“The memory effect could in fact persist for several days, but we don’t currently have the instruments needed to measure that,” says Prof. Matioli.
The importance of memory effect
The research team’s discovery is considered to be quite significant. The memory effect reveals a property of vanadium dioxide not previously known.