Super-high Curie temperature ferroelectrics and superior TC tunability: lattice instability and ferroelectric phase transitions

Abstract

Ferroelectric materials with high Curie temperatures, TC, and tuning of the TC over a large temperature range are very important for the basic 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 = 1342 °C and its family. The lattice instability of the high-temperature ferroelectric phase transitions is also discussed. The superior tunability of the TC is achieved by the substitution of cations at the A- and B-sites in the perovskite-like structures. The variation of the soft optic and relaxation modes and elastic anomalies related to structural phase transitions were discussed in relation to the A- and B-site substitutions of oxygen octahedral ferroelectrics, especially Ba2NaNb5(1-x)Ta5xO15 with a tungsten bronze structure and (BaxSr1-x)2Nb2O7, Sr2(Nb1-xTax)2O7 with the perovskite slab structure.