A discovery concerning the self-organization of ferroelectric and antiferroelectric crystals through the interplay of their particle shape and dipolar interactions could lead to new approaches to developing highly functional materials. The putatively useful properties of such materials might be manifest through the cross reaction in which electric/magnetic order and deformation or thermal response are combined; exploiting the phase transition between ferroelectric ordered phase and antiferroelectric ordered phase.

The electrical and mechanical responses of crystalline materials are critical to many applications. Moreover, control coupled effects represents a central tenet of materials science and allows devices such as ultrasonic generators and non-volatile memory to be constructed. However, despite our ever-increasing prowess in controlling such materials, the physical principles that underpin the phenomena we use, the controllability through lattice organization, remains something of a mystery. Now, researchers at The University of Tokyo Institute of Industrial Science have built a new model based on the conflict between different lattice interactions and explain the implications of what they have found using this model in the journal PNAS.  [K. Takae et al., Proc Natl Acad Sci (2018) DOI: 10.1073/pnas.1809004115].

It is conventional wisdom that the arrangement of atoms or molecules within a crystal structure and the relationship between those units ultimately determines the properties of the bulk material. It is one of the reasons why crystal structure determination is such an important part of chemical, biochemical and materials science. For materials that are ferroelectric and antiferroelectric, ordering describes long-range dipole based arrangements of molecules in a lattice, which give rise to specific properties. However, there are ordered materials of this sort that can exhibit electrical switchability as well as interesting cross-coupling effects. Understanding the behavior of such crystal structures can have immediate tangible practical benefits.

"Our model was designed to probe the simple physical principle that controls ferroelectric and antiferroelectric order by varying the shape of the molecules in a dipolar lattice," explains team member Hajime Tanaka. "We also compared the resulting effects on the electrical, dynamic, and thermal properties."

The team created a simple self-organizational model based on spherical particles with a permanent dipole. This allowed them to establish the importance of the energetic frustration between the anisotropic steric and dipolar interactions in the self-organization process.

"Understanding the underlying principle that governs ferroelectric and antiferroelectric organization and transitions is key to achieving optimal control of the properties that are already being utilized in many different applications," lead author of the paper Kyohei Takae adds. "By carrying out thorough modeling of these systems we hope to be able to enhance the rational design of a wide range of materials including non-volatile memory devices - hard drives and flash memory--and electro-mechanical actuators, used in robotic instruments."

David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase. His popular science book Deceived Wisdom is now available.