Ferroelectric materials are made into "rubber bands" for the first time, unlocking more shapes for wearable devices

If ferroelectric materials, commonly used in memory, piezoelectric components and other fields, gain elasticity like a rubber band, it is expected to make sensors more versatile and mobile phones easier to bend and fold.

On August 4, the international academic journal "Science" published the scientific research results of the flexible magnetoelectric functional materials and devices team of the Ningbo Institute of Materials, Chinese Academy of Sciences - the first in the world to develop a new polymer ferroelectric with both elastic recovery and ferroelectricity. Materials, effectively solve the problem of traditional ferroelectric materials being difficult to maintain stable performance under large deformation, and fill the gap in the field of elastic ferroelectric materials.

The difference between traditional ferroelectric materials and elastic ferroelectric materials. Photo courtesy of scientific researchers

Ferroelectric materials are prone to failure when stretched

"Ferroelectric materials are a kind of magical insulating functional materials. The surface is self-charged. When there is no external electric field, these charges are in a disordered state." The corresponding author of the paper, researcher Hu Benlin of the Ningbo Institute of Materials, Chinese Academy of Sciences, said that once an electric field is applied, On ferroelectric materials, these charges are rearranged, and the arrangement changes as the electric field changes.

In addition, ferroelectric materials also have memory capabilities. Even if the electric field no longer acts, the arranged charges will remain in their original state without changing. This allows ferroelectric materials to have high dielectric constant, piezoelectricity, pyroelectricity, electric refrigeration and other properties, and can be used in electronic products such as computer memories, high-precision motors, ultra-sensitive sensors and sonar equipment, as well as mobile phones, One of the essential materials in electronic devices such as tablet computers.

In recent years, research on flexible wearable devices has continued to be hot. Such devices are considered to have broad application prospects in fields such as portable mobile electronic devices and human movement detection. As one of the important materials for manufacturing flexible wearable devices, ferroelectric materials can contribute to the development of this industry if they can be made elastic.

"However, it is difficult to study and prepare elastic ferroelectric materials." Hu Benlin explained that traditional ferroelectric materials are mainly linear structures, with regularly arranged parts forming crystalline regions to provide ferroelectricity, while the remaining molecular chains are intertwined with each other. Since there is no covalent connection between linear molecular chains, once external force is applied, the entanglement will be unraveled, which will lead to the destruction of the crystalline region and affect its ferroelectricity.

Gao Liang, the first author of the paper and a master's student jointly trained by the School of Nanotechnology at the University of Science and Technology of China and the Ningbo Institute of Materials, Chinese Academy of Sciences, added that the crystal itself has almost no elasticity, and the stretch rate is generally less than 5% and has no rebound ability, so It is difficult for ferroelectric materials to balance ferroelectricity and elasticity.

"Micro-cross-linking method" weaves "fishing net" to gain elasticity

Can’t sugarcane be sweet at both ends? In this study, the researchers used precise design and control of the material structure to prepare an elastic material that still has good ferroelectric response under high-frequency large deformation. After stretching it to twice its original length, it can not only It maintains the original ferroelectricity and can quickly return to its original state after the external force is removed, achieving a balance between ferroelectricity and elasticity of ferroelectric materials.

The method of preparing elastic ferroelectric materials is called the "micro-cross-linking method" by the team - using a small amount of soft chain-like polymers to cross-link the amorphous winding parts around the ferroelectric crystals, intertwining with each other to form an elastic fishing net. shape structure. Similar to placing crystals and winding parts in a "fishing net" through chemical cross-linking, a ferroelectric "rubber band" with good elastic recovery capabilities is made.

Hu Benlin said that the team tried dozens of materials before finding a suitable chain polymer. This fishnet-like structure loosely connects the ferroelectric crystals together. When an external force is applied, it can produce reversible deformation to absorb the external force and avoid damage to the crystalline part by the external force, so that the material can still remain stable within a certain stretching range. Ferroelectricity; when the external force is removed, this elastic fishnet-like structure can return to its original state.

"In addition, precise control of the amount of chain polymer can ensure that the ferroelectric crystals can be evenly distributed in the cross-linked network, so that the material can maintain a good ferroelectric response after cross-linking." Hu Benlin said that this elasticity Ferroelectric materials can withstand thousands of repeated stretches without their ferroelectric properties remaining stable. It can return to its original shape after being stressed, avoiding permanent deformation, greatly improving reliability and service life, and expanding the scope of use.

The reviewer of the "Science" journal commented that in the century-old history after the discovery of ferroelectric materials, compared with the tensile strain of no more than 0.2% for ferroelectric ceramics and the elastic recovery of less than 2% for polymer ferroelectric materials, This is a breakthrough work that opens up a new subject direction of "elastic ferroelectrics".