Nagoya University researchers synthesized new multilayered perovskites, finding that their ferroelectric properties change based on the number of layers. This discovery could greatly enhance future electronic device development.
A research team from Nagoya University in Japan has successfully synthesized 4- and 5-layered versions of the key electrical material, perovskite. In their analysis of the material’s ferroelectric properties, they discovered a unique feature: the ferroelectric mechanisms switch based on whether the number of layers is odd or even. This finding is expected to significantly advance the development of new electronic devices due to the material’s versatile characteristics. The study was published in the Journal of the American Chemical Society.
Perovskites are a class of materials that share a specific crystal structure made up of calcium titanium oxides. Electronic devices often use perovskites because they exhibit a property called ferroelectricity. Ferroelectricity allows for the control and reversal of electric polarization by an external electric field. This feature makes perovskites useful for electronic devices such as memory, capacitors, actuators, and sensor devices, which use on and off states.
To improve functionality and reduce the environmental impact of these products, researchers are developing new compositions, structures, and lead-free ferroelectrics. Perovskites, especially Dion-Jacobson (DJ)-type layered perovskites, are becoming an important class of materials in this research.
Ferroelectric Properties of DJ-Type Perovskites
DJ-type perovskites have a layered octahedral structure, which makes the layers asymmetrical, giving them ferroelectric properties. The ferroelectric properties are caused by the shifting of positive and negative ions when an outside field is applied, causing rotation and tilting of the octahedra due to size mismatches. This tilting lowers the symmetry of the material, further contributing to ferroelectric behavior.
Minoru Osada, of Nagoya University’s Institute of Materials and Systems for Sustainability (IMaSS), explained that researchers consider layered perovskites unexplored materials due to the decline in thermodynamic stability as the thickness of the perovskite layers increases.
To overcome this, the research group developed a new synthesis method, known as the template synthesis method, that enables the synthesis of multilayer structures by layering perovskite layers one by one and aligning their octahedrons in the manner of building blocks.
“In the template synthesis method, the number of layers can be increased by one layer by using a three-layer system as the starting material and reacting it with SrTiO3,” Osada said. “By repeating the reaction, the number of perovskite layers can be digitally controlled according to the number of reactions, allowing the synthesis of a multilayer structure. By applying the template synthesis method, we synthesized four- and five-layered perovskites for the first time.”
Unique Behavior of Multilayer Perovskites
Intriguingly, when they tested the material, they found that it behaved strangely, exhibiting different dielectric constants and Curie temperature depending on the number of layers.
“We found that the number of layers plays an important role in this system, and that it has a unique function to switch to the conventional direct ferroelectricity model when the number of layers is odd and to the new indirect ferroelectricity model when the number is even,” Osada said.
Their approach provides a new opportunity to expand the range of ferroelectric materials beyond the thermodynamically stable phases. This achievement is expected to greatly expand the material search space in the development of ferroelectrics and provide important guidelines for the development of new materials and functions that are difficult to realize with existing materials and technologies.
Reference: “Atomic Layer Engineering of Ferroelectricity in Dion–Jacobson Perovskites” by Shu Morita, Daisuke Urushihara, Keita Nishibashi, Makoto Kobayashi, Eisuke Yamamoto, Toru Asaka, Hiroshi Nakajima, Shigeo Mori and Minoru Osada, 26 August 2024, Journal of the American Chemical Society.
DOI: 10.1021/jacs.4c09214