Ferroelectrics are a special class of materials that can be switched between two opposite electrical polarization states by applying an external electric field. This property makes them ideal for use in a variety of electronic devices, such as memory chips and sensors.
In recent years, there has been a growing interest in developing organic ferroelectrics as an alternative to inorganic oxides. Organic ferroelectrics have a number of advantages over inorganic oxides, including their flexibility, low cost and ease of processing. However, organic ferroelectrics have typically been less efficient and stable than their inorganic counterparts.
The new organic ferroelectric material developed by the OIST-led team is based on a molecule called [N-(4-bromobenzyl)-2,5-dimethylpyrrole-3-carboxamide]. This molecule is a member of a class of compounds known as "triazoles," which have been shown to have promising ferroelectric properties.
The researchers found that the new triazole-based organic ferroelectric material had a high dielectric constant, which is a measure of its ability to store electrical energy. The material also exhibited a high degree of polarization, which is a measure of its ability to switch between its two opposite electrical polarization states.
In addition, the new organic ferroelectric material was found to be stable at high temperatures and under high electric fields. This makes it a promising candidate for use in electronic devices that operate under harsh conditions.
The development of this new organic ferroelectric material is a significant step forward in the field of organic electronics. This material could potentially be used in a variety of electronic devices, such as memory chips, sensors and energy storage devices.
A research team led by Professor Takeharu Sakurai from the Nonlinear Optics Unit at OIST's Materials and Devices Unit investigated a small organic molecule and discovered it to have high electric polarization. The result provides a strong indication of the material potentially becoming an organic ferroelectric. Ferroelectricity is a phenomenon where spontaneous electric polarization in a material can be reversed—often by applying an electric field. For example, ferroelectric materials are widely used in capacitors, which store electric charges or electric energy, and in sensors that detect changes in acceleration, motion or temperature.
Although organic molecules possess interesting electronic, magnetic, optoelectronic and mechanical properties, organic ferroelectrics have been difficult to synthesize due to their crystal structures, which prevent the formation of spontaneous electric polarization.
Ferroelectric oxides are conventionally used, but these are typically inorganic materials composed of metal ions and oxygen, and they are difficult to process and are vulnerable to external forces. Developing an organic ferroelectric composed of carbon, hydrogen, nitrogen, oxygen, sulfur, and other elements would potentially resolve such problems.
However, the team led by Professor Sakurai used a small organic molecule named [N-(4-bromobenzyl)-2,5-dimethylpyrrole-3-carboxamide] with a two-dimensional layered structure and succeeded in synthesizing the organic ferroelectric. The synthesized material shows a high electric polarization at approximately 8 micro-Coulombs per square centimeter (μC/cm2) with an applied electric field of 104 volts per micrometer (V/μm).
For comparison, the research team evaluated organic and inorganic ferroelectrics reported previously and found that the synthesized organic ferroelectric exhibits a sufficiently high electric polarization. Although the electric polarization of the synthesized material is still smaller than that of widely-used inorganic oxide ferroelectrics, it is on the same order as that of polymers, which are widely-used organic electronics materials.
Professor Sakurai is aiming to further improve the electric polarization of the organic ferroelectric by modifying the material structure and using dopants. "To achieve electric polarization comparable to or better than widely-used inorganic oxide ferroelectrics, it will likely take some more time," says Sakurai. "Nevertheless, we are optimistic about our newly developed ferroelectric material, which could be used as a capacitor, piezoelectric sensor/actuator, or as a component of nonvolatile organic memory devices in the future."
