High Curie temperatures of ferroic materials such as ferroelectrics, ferromagnetics, and ferroelastics have attracted much attention, while their physical origins are not yet clarified. The year 2020 marks hundred years since the discovery of the phenomenon of ferroelectricity. Ferroelectrics have a rich of functionality such as piezoelectric, electro-optic, nonlinear optic, electrocaloric, energy storage, pyroelectric properties. Ferroelectric materials with high Curie temperatures, TC, and tuning of the TC over a large temperature range are very important for the fundamental sciences and engineering. This paper reviews the various types of high-temperature ferroelectrics with perovskite, bismuth layered, tungsten bronze, and perovskite slab structures, especially Sr2Nb2O7 with TC = 1342oC and its family. The superior tunability of the TC is achieved by the substitution of cations in the A- and B-sites of perovskite-like structures. The origin of ferroelectricity with high TC is discussed.
S. Kojima studied at Department of Physics, Faculty of Science, University of Tokyo, Japan, receiving Bachelor of Science in 1974 and Doctor of Science in 1979. He was promoted to the position of full professor at University of Tsukuba, Japan, and worked as the chair of Institute of Materials Science, University of Tsukuba from 2011 to 2015. He continues his research and teaching as professor emeritus of University Tsukuba. Throughout his carrier, he has been a member of editorial boards for these professional magazins, Ferroelectrics, Materials, Current Applied Physics, Japanese Journal of Applied Physics. He was the chairman of the organizing committee of the 8th Russia/CIS/Baltic/Japan Symposium on Ferroelectrics, Tsukuba, 2006 and the 53th Ultrasonic Electronics Symposium, Tokyo, 2014.
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