Recently, Professor Li Wei, School of Materials Science and Engineering and National Institute for Advanced Materials, Nankai University, at the invitation of Science（journal）, published the prospective article “Metal-Free Perovskite Ferroelectrics”.
As a class of certain materials with a spontaneous electric polarization that can be reversed by the application of an external electric field, ferroelectric materials are widely used in the fields of capacitance, sensing, and data storage. Since the 1940s, perovskite oxide has occupied almost half of the industrial ferroelectric materials. However, due to the high cost of preparation and production of perovskite oxide film materials and the presence of toxic heavy metal components, researchers have been working to find alternatives to their components.
Iron electrodeposition mechanism in perovskiteoxides BaTiO3 (left) and metal-free perovskites (right).
The XiongRengen’s team of Southeast University used molecular design principles to replace metal sites in perovskites with NH4+ and assembled a series of metal-free perovskite ferroelectrics by hydrogen bonding, published in the recent issue of Science. (Science 2018, 361, 151). They introduced asymmetric ammonia ions to direct the synthesis of perovskite ferroelectric materials, which are comparable to classical ferroelectrics in performance. Li Wei believes that the superior ferroelectric property of metal-free perovskites has the same application prospects with perovskite oxide ferroelectrics. In addition, the multi-polarization properties of such materials make them easily flipped under the action of an external electric field and are thus easily polarized. Li Wei further noted that the inclusion of a large amount of organic components in such materials makes them flexible in structure, facilitating film formation and regulation and control of performance. In addition, the new type of metal-free perovskite ferroelectrics has many advantages such as ease of synthesis, low cost, and low density.
In the article, Li Wei forecasted many issues worthy of exploration in the field. For instance, the binding force between NH4+ and halogen ions is not completely limited to hydrogen bonding, and the electron nature of its bonding is worthy of further study. At the same time, the symmetry breaking of such metal-free ferroelectric perovskites is accompanied by large lattice strain and unique twin wall dynamics. A deep understanding of these properties from a microscopic perspective will help to explore its potential applications on high density memory devices. In addition, the chirality of these metal-free perovskites makes the arrangement of electric dipoles more confusing, and understanding the coupling mechanisms of chiral and electric dipoles at the macro and nano scales may be helpful in discovering more noveltyof such materials.
Source: Nankai News
Written by Junhui Wu
Edited by Kuqing Li and Ruoyan Yan