The group explains how they managed to synthesize 4- and 5-layered perovskites, uncovering the distinctive ferroelectric nature of these layered perovskites. This development could be a key step toward more advanced electronic devices that are not only operable on low-power and high output speed, but also able to sync with the sustainable environment.
Unlocking the Secrets of Layered Perovskites
Perovskites are materials having a certain type of crystal structure that has been fast-tracked for use in electronic devices. They have a property called ferroelectricity, which means that electric polarization can be controlled and reversed by an external electric field. This feature provides very exciting application prospects, such as memory devices, capacitors (energy storage), actuators and sensors.
Over the years, researchers have discovered new compositions and configurations of lead-free ferroelectrics to improve properties and make these products more environmentally friendly. One promising direction is to use a Dion-Jacobson (DJ) type layered perovskite since DJ-type structures are the configuration of octahedrons, the oxygen framework bounding 3 octahedrons in edge-sharing and the other 3 octahedra in face-sharing planes along [001] which makes it favourable for the production of ferroelectric phase. The tradeoff with that was the reduction in thermodynamic stability as the perovskite layers increased in thickness.
Defying Thermodynamic Limitations
To resolve the potential difficulty caused by these organic solvents, scientists at Nagoya University developed a new synthesis method that does not rely on such specific conditions: [The researchers] led by Minoru Osada have named this innovative approach the template synthesis method. They can therefore deploy this production technique in stacking perovskite layers on top of each other—each with its octahedrons in the so-called building block, an octave at a time.
In the template synthesis method he says, “If a three-layer system is used for a starting material and reacted with SrTiO3, an additional layer can be added to the existing number of layers.” This approach is used reciprocally, making the number of perovskite layers determined digitally by a multiplicity of reactions to synthesize a multilayer structure. The technique enabled the researchers, led by MIT’s Samuel Stranks and Feliciano Giustino from the University of Oxford (both affiliated with the London Centre for Nanotechnology), to create four- and five-layered perovskites for the first time overcoming thermodynamic constraints that had stymied realization of such multi-layered structures in prior efforts.
Conclusion
This new capability to generate multilayered perovskites might lead to innovations in the fields of low-energy-consuming LED lighting and other future high-tech electronic technologies. The researchers thus overcame the thermodynamic hurdles in thickening down ferroelectric layers, which can serve as a general guiding principle for further explorations of versatile ferroelectric properties and functionalities. This breakthrough is anticipated to significantly broaden the search space for materials in ferroelectrics and pave a new way for material discovery and technology that was hitherto considered impossible.
