For a long time now, ferroelectric materials with electric polarization which can be reversed by electrical filed, have received significant attention owing to their technological attributes including large piezoelectric characteristics and ferroelectric hysteresis necessary for nonvolatile memories. ABO3 perovskites are among the many ferroelectric materials that have been good candidates for technological and fundamental interests due to their superior polarization and excellent response of their polarization to stress as well as electric fields.
Pb(ZrxTi1-x)O3 as a ferroelectric material, has been commercialized for decades. However, the presence of lead in this compound is a critical issue for the strict environmental requirements. Therefore, finding a new ferroelectric material with tin belonging to the same group as lead would be a groundbreaking research.
Fortunately, researchers led by Professor Sang-Wook Cheong from Rutgers University fabricated for the first time ferroelectric tin insulator designed with switchable electric polarization. The tin insulator, which was lead-free, exhibited ferroelectricity at ambient conditions and was perfect for ferroelectric applications. Their work is now published in journal, Advanced Materials.
The authors synthesized polycrystalline tin insulator Sr3Sn2O7 using solid-state reaction approach. They realized this through the stoichiometric mixture of Strontium carbonate and tin oxide. The mixture was pelletized, sintered and grinded. The authors confirmed that the polycrystalline tin insulator was a good insulator through the dielectric constant and loss of the Sr3Sn2O7 as a function of temperature and frequency.
The authors applied an in-plane external electric field using a focused electron beam. In a bid to understand the ferroelectric switching mechanism, the authors performed a dark-field transmission electron microscopy analysis. They observed various patches with 180° polarization represented by black arrows. They induced an in-plane electric field represented by black arrow with a white edge by focusing an electron beam on the sample’s edge. Domains with polarization aligned parallel to the induced electric field appeared immediately.
The authors realized two ferroelectric 180° domain walls. One was a ferroelectric charged domain wall while the other was noncharged. Owing to charge dissipation after removing the electron beam, the authors observed an evolution of the ferroelectric domain walls from the images taken from the dark-field transmission electron microscopy. They also observed that the noncharged domain walls moved in a way to decrease the new domain region and they disappeared with approximately 24.6 nms-1. The domain walls stopped at a distorted region. During this time, the charged domain walls didn’t move.
The authors discovered that the layered tin-based insulator with a large optical gap, which was approximately 4.13eV exhibited switchable polarization at ambient temperature. This indicated that they managed to fabricate the first room temperature insulating ferroelectric material containing tin ions. The authors recorded a net electric polarization of about 0.24uC cm-2 at room temperature. This originated from hybrid ferroelectricity. From the results of electron diffraction, and dark-field transmission electron microscopy analyses, they observed the presence of 180° and 90° ferroelectric domain walls, and a few of them were found to be charged. These discoveries revealed the nature of tin containing ferroelectric and provide great opportunities for lead-free ferroelectric applications.
Yazhong Wang1, Fei-Ting Huang1, Xuan Luo2, Bin Gao1, and Sang-Wook Cheong1. The First Room-Temperature Ferroelectric Sn Insulator and Its Polarization Switching Kinetics. Advanced Materials, volume 29 (2017), pages 160-288.Show Affiliations
- Rutgers Center for Emergent Materials and Department of Physics and Astronomy, Rutgers University, Piscataway, NJ, 08854, USA.
- Laboratory for Pohang Emergent Materials and Max Plank POSTECH Center for Complex Phase Materials, Pohang University of Science and Technology, Pohang, 790-784, South Korea.
Go To Advanced Materials