Developing flexible ferroelectric material for more efficient bendable electronics

Significance 

Piezoelectric materials are commonly used in guitars, loudspeakers, sensors and electric motors. For instance, a piezoelectric pick-up is a device used in an electric guitar to convert the vibrations from the strings into an electric signal, which is then processed for music recording or to be amplified through loudspeakers.  Ferroelectric crystals were first discovered in 1920 and have been used to make piezoelectrics for over 70 years, as they are easily integrated into electrical devices. However, they are brittle and inflexible, bending only 0.5%, which largely limits their application in electronic devices such as actuators (parts that convert an electric control signal into mechanical motion, for example, a valve that opens and closes). To this note,

Scientists at Nanyang Technological University in Singapore led by Professor Fan Hong Jin from the School of Physical & Mathematical Sciences created a new material to overcome these limitations. The research work is published in the research journal Nature Materials,. Also part of the team is Professor Junling Wang from the Southern University of Science and Technology, China.

To develop a flexible ferroelectric material, the researchers modified the chemical structure of a hybrid ferroelectric compound C6H5N(CH3)3CdCl3, or PCCF in short, which can potentially bend up to a hundred times more than traditional ferroelectrics. To increase the material’s range of movement further, the scientists modified the chemical makeup of the compound by substituting some of its chlorine (Cl) atoms for bromine (Br), which has a similar size to chlorine, to weaken the chemical bonds at specific points in the structure. This made the material more flexible without affecting its piezoelectric qualities.

The new material when it is bent, it generates electricity very effectively and could be used for better ‘energy harvesting’—potentially recharging batteries in gadgets just from everyday movements. The novel material is both electrostrictive and piezoelectric. Its electrostrictive properties means it can change shape when an electric current is applied, while piezoelectric means the material can convert pressure into electric charges. When an electric field is applied, the atoms that make up electrostrictive materials shift, causing the material to deform and flex. When piezoelectrics are compressed, the pressure is converted to electric charges which accumulate in the material.

The authors found that when an electric field is applied, the new hybrid material could be strained up to 22%, the highest strain reported in a piezoelectric material so far. This far surpasses conventional piezoelectric materials that only deform up to 0.5% when a current is passed through it. The new material is also more energy-efficient than other piezoelectric and electrostrictive materials.

Some ferroelectrics also contain lead, which is toxic, and its presence in piezoelectric devices is one of the reasons why electronic waste is challenging to recycle. Traditional ferroelectrics such as perovskite oxides are also unsuitable for flexible electrical devices that are in contact with the skin, such as wearable biomedical devices that track heart rate. The new ferroelectric material is 40 times more flexible than similar electrostrictive materials, it may be used in highly efficient devices such as actuators and sensors that flex when an electric field is applied. With its superior piezoelectric properties, the material can also be used in mechanical devices that harvest energy when bent, which will be useful to recharge wearable devices. The authors believe they can substantially improve on this performance in future by further optimizing the chemical composition, and we believe this type of material could play a key role in the development of wearable devices for the Internet of Things (IOT), one of the key technologies enabling the 4th Industrial Revolution.

The new material is easy to manufacture, requiring only solution-based processing in which the crystal forms as the liquid evaporates, unlike typical ferroelectric crystals that require the use of high-powered lasers and energy to form. When an electric field was applied to the new PCCF compound, the atoms in it shifted substantially more than the atoms in most conventional ferroelectrics, straining up to 22% far more than conventional piezoelectric materials. In a nutshell, Nanyang Technological University, Singapore (NTU Singapore) successfully developed a new material, that when electricity is applied to it, can flex and bend forty times more than its competitors, opening the way to better micro machines.

Developing Flexible crystal, designed for more efficient bendable electronics - Advances in Engineering
FIGURE: A close up of the new piezoelectric crystal developed by NTU scientists, which can flex up to 40 times more than the conventional ferroelectric crystals typically used in small actuators and sensors.

About the author

WANG Junling
Chair Professor, Department of Physics

Professor WANG Junling obtained his B.S. degree from Nanjing University in 1999, and Ph.D. degree from University of Maryland, College Park in 2005. After spending one year at PennState University as a postdoc, he joined Nanyang Technological University, Singapore as an Assistant Professor in 2006. He was promoted to Associate Professor with tenure in 2011 and Professor in 2017.

His research activities focus on 3D and 2D multiferroic materials. These materials possess a wide range of exotic properties such as ferroelectricity, ferromagnetism, and multiferroicity. The long-range orders and cross-couplings between them lead to fascinating physics and various applications. He has published >150 papers in high impact journals, including Science, Nature Communications, Science Advances, PRB and APL. His work has been cited more than 11300 times.

Reference

Yuzhong Hu, Lu You, Bin Xu, Tao Li, Samuel Alexander Morris, Yongxin Li, Yehui Zhang, Xin Wang, Pooi See Lee, Hong Jin Fan & Junling Wang. Ferroelastic-switching-driven large shear strain and piezoelectricity in a hybrid ferroelectric. Nature Materials (2021). DOI: 10.1038/s41563-020-00875-3

Go To Nature Materials

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