Plastic crystals could improve production of memory devices

Researchers at Japan's Hokkaido University have developed a novel ferroelectric plastic crystal that could accelerate the development of more flexible, cost-efficient and less toxic ferroelectrics than those currently in use.

The crystal is ferroelectric above room temperature, then turns into a plastic, more pliable phase at higher temperatures. At the higher temperatures, the molecules in the crystal have randomly different polarity axes, but they can be aligned in one direction by applying an electric field as the crystal cools, bringing it back to a ferroelectric state.

Being able to control the polarity in this manner addresses a major challenge previously faced by researchers working with organic compound-based ferroelectric crystals. These are less symmetric than inorganic crystals, and can thus be polarised only in one direction leading to a very weak overall polarisation of randomly oriented crystals.

A distinct advantage of this particular crystal is its transition to a plastic state when heat is applied. This plasticity - as opposed to fracturing that occurs in regular organic and inorganic crystals when a mechanical stress is applied - makes it extremely advantageous for use as a thin ferroelectric film in devices, such as non-volatile ferroelectric random-access memory devices, which maintain memory when the power is turned off.

Exploring crystals composed of molecules similar to quinuclidine could lead to the discovery of more ferroelectric crystals, write the researchers in their paper published in the journal Nature Chemistry. Chemical modifications of the molecules' constituent ions could also improve their performance, the researchers add.