Ferroelectrics are a class of materials that exhibit a spontaneous electric polarization that can be reversed by the application of an external electric field. Unlike ferromagnetic materials that possess a spontaneous magnetic moment, ferroelectrics possess a spontaneous electric dipole moment. This property makes them valuable for various applications, including their use as actuators. Actuators are devices that convert electrical, mechanical, or thermal energy into motion. Ferroelectric materials can act as actuators due to their ability to undergo a change in shape or size when an electric field is applied. This phenomenon is known as the piezoelectric effect, and it is the basis for the actuation capabilities of ferroelectrics. When a voltage is applied across a ferroelectric material, the electric field causes a reorientation of the electric dipoles within the material, resulting in a change in its shape or dimensions. This change can be either an expansion or contraction, depending on the specific material and its crystal structure. The piezoelectric effect in ferroelectrics is reversible, meaning that the material can return to its original state when the electric field is removed. The actuation capabilities of ferroelectrics find applications in various fields, for instance, ferroelectric actuators are used in MEMS devices for precise positioning, sensing, and control. They can be integrated into tiny mechanical systems, such as microvalves, microgrippers, or micro-mirrors, to provide precise and rapid actuation. The piezoelectric response of ferroelectrics allows for nanoscale positioning and high-speed actuation in MEMS applications. Ferroelectric materials are also utilized in ultrasonic transducers for medical imaging, non-destructive testing, and other applications that require the generation and detection of high-frequency sound waves. By applying an alternating voltage to a ferroelectric transducer, it vibrates at ultrasonic frequencies, producing sound waves for imaging or sensing purposes. Moreover, ferroelectric deformable mirrors are used in adaptive optics systems to correct aberrations in optical systems caused by atmospheric turbulence or imperfections in lenses and mirrors. By applying an electric field to the ferroelectric actuator, the mirror’s shape can be adjusted in real-time, compensating for distortions and enhancing the quality of the optical system. Furthermore, ferroelectric materials can also be used in energy harvesting devices. When subjected to mechanical vibrations or deformations, the piezoelectric properties of ferroelectrics can convert the mechanical energy into electrical energy, which can be stored or used to power electronic devices. This technology is particularly useful in applications where ambient vibrations or mechanical stresses are available, such as in wearable devices or industrial machinery.
Single-layer or 2D materials are typically made up of a single layer of atoms, meaning they are only a few nanometers thick. They have received significant attention in recent years due to their physical, electrical, chemical and optical properties, which makes them useful in applications ranging from consumer electronics to medical and industrial technologies. To this account, Dr. Jun-Jie Zhang, Dr. Tariq Altalhi, and led by Professor Boris Yakobson from Rice University uncovered a new property of ferroelectric 2D materials that could be exploited as a feature in future devices. Because they bend in response to an electrical stimulus, single-layer ferroelectric materials can be controlled to act as a nano-scale switch or even a motor. The research work is now published in the peer-reviewed Journal, ACS Nano.
The authors found that there is a connection or coupling between the ferroelectric state and the bending or flexing of the material. The work combines the discovery or prediction of a fundamental property of a class of 2D materials with a practical application angle. Polarization drives the larger atoms to one side of the 2D-material layer and the smaller atoms to the other side. This asymmetrical distribution of the atoms or ions causes the material surface to bend in ferroelectric state. So instead of remaining flat, in ferroelectric state the material will bend. It is possible to switch polarization by applying electrical voltage you will control the direction in which it will bend. This controllable behavior is what makes an actuator. In a nutshell, an actuator is any device that translates a signal in many cases an electrical signal, but it can be a different kind of signal into mechanical displacement or, in other words, movement or work.
The research team looked at 2D indium phosphide (InP) as a representative of the class of ferroelectrics for which it predicts this property. They found the behavior very fast, very sensitive, which means that with a very tiny local signal you can maybe switch on a turbine or electrical engine, or control adaptive-optics telescopes’ mirrors. That’s basically the essence of these actuators. In summary, ferroelectric materials exhibit the piezoelectric effect, allowing them to act as actuators by changing shape or size in response to an applied electric field. The actuation capabilities of ferroelectrics enable precise control and manipulation in various fields, contributing to advancements in technology and improving device performance.
Zhang JJ, Altalhi T, Yakobson BI. Flexo-Ferroelectricity and a Work Cycle of a Two-Dimensional-Monolayer Actuator. ACS Nano. 2023;17(5):5121-5128. doi: 10.1021/acsnano.3c00492.