Abstract
Hard-mode Raman spectroscopy was applied to analyze the temperature-induced transformation processes in perovskite-type single crystals of (NBT- in a wide temperature range between 100 and 1010 K and a composition range of across the morphotropic phase boundary (MPB). The results show abundant uncoupled ferroic structural distortions even at 1010 K and coexistence of two types of mesoscopic-scale ferroic order at lower temperatures. Octahedral tilting is typical of pure NBT, while the incorporation of A-site suppresses the tilting and promotes the off centering of octahedra. The temperature evolution of the phonon modes clearly reveals the two macroscopically observed critical temperatures and as well as, in the case of , two characteristic temperatures and preceding the and , respectively, which are attributed to mesoscopic-scale antiferroelectric and ferroelectric coupling processes within the A-site-cation subsystem. At the two sublattices, off-centered A-site cations and off-centered B-site cations, remain incoherent in the entire temperature range. Only when the amount of Ba reaches the two subsystems couple dynamically, which can explain the enhancement of properties at the MPB. The overall ferroic distortion, however, has a minimum at the MPB, probably because at the ferroelectric coupling between B-site cations is reduced to a greater extent than the enhancement of ferroelectric coupling between A-site cations.
4 More- Received 11 September 2017
- Revised 2 November 2017
DOI:https://doi.org/10.1103/PhysRevB.96.214102
©2017 American Physical Society