Research suggests a new class of ferroelectric materials

Ferroelectric materials have a wide variety of applications. From electro-optical devices to supercapacitors, their unique piezoelectric responses make ferroelectrics instrumental throughout industry. Part of the complexity in developing these materials is that, in order to produce adequate electric signals, they must be stabilized on the brink of phase transition.

Everhardt et al. met this challenge by growing BaTiO₃, a chemically simple material, on NdScO₃ substrates using strain engineering. The authors were able to freeze transitional states, which were enabled by polarization rotation gradients and engineered in such a way that the BaTiO₃ films can appear with polar phases of different orientations. This allows them to develop huge, temperature-independent dielectric responses and large piezoelectric responses.

“This physical method creates a gradual change in the symmetry which is independent of the temperature – creating a material with the same robust properties at a very broad temperature range,” said author Noheda.

The authors explained that, unlike traditional ferroelectrics, transitional ferroelectrics are not in a well-defined crystalline or periodic state, but in a state that bridges two)phases. As such, they have a crystal structure that is intermediate between the two phases. Using their method, they were able to achieve this using a non-toxic and compositionally simple material.

“This was previously achieved by playing with the composition of the material. Usually, this requires very specific compositions and very often chemical elements that are toxic,” said Noheda. “But here, we show that epitaxial strain (strain engineering) can also be used to achieve that state in compositionally simple and non-toxic ferroelectrics.”

The authors intend on investigating the limitations of this approach by re-creating it using the same transitional state with other simple materials.

Source: “Temperature-independent giant dielectric response in transitional BaTiO₃ thin films,” by Arnoud S. Everhardt, Thibaud Denneulin, Anna Grünebohm, Yu-Tsun Shao, Petr Ondrejkovic, Silang Zhou, Neus Domingo, Gustau Catalan, Jiří Hlinka, Jian-Min Zuo, Sylvia Matzen, and Beatriz Noheda. Applied Physics Reviews (2020). The article can be accessed at https://doi.org/10.1063/1.5122954 .