Abstract
The results of high-resolution measurements of the diffuse X-ray scattering produced by a perovskite-based Na0.5Bi0.5TiO3 ferroelectric single crystal between 40 and 620 K are reported. The study was designed as an attempt to resolve numerous controversies regarding the average structure of Na0.5Bi0.5TiO3, such as the mechanism of the phase transitions between the tetragonal, P4bm, and rhombohedral | monoclinic, R3c | Cc, space groups and the correlation between structural changes and macroscopic physical properties. The starting point was to search for any transformations of structural disorder in the temperature range of thermal depoling (420-480 K), where the average structure is known to remain unchanged. The intensity distribution around the {032} pseudocubic reflection was collected using a PILATUS 100K detector at the I16 beamline of the Diamond Light Source (UK). The data revealed previously unknown features of the diffuse scattering, including a system of dual asymmetric L-shaped diffuse scattering streaks. The topology, temperature dependence, and relationship between Bragg and diffuse intensities suggest the presence of complex microstructure in the low-temperature R3c | Cc phase. This microstructure may be formed by the persistence of the higher-temperature P4bm phase, built into a lower-temperature R3c | Cc matrix, accompanied by the related long-range strain fields. Finally, it is shown that a correlation between the temperature dependence of the X-ray scattering features and the temperature regime of thermal depoling is present.
Highlights
Na0.5Bi0.5TiO3 (NBT) is a ferroelectric material that is interesting both as the foundation of many potential lead-free piezoelectrics (Takenaka et al, 2008) and as a model system for the crystallography of perovskites (Mitchell, 2003)
The first aim of this work is to reinvestigate the exact topology of the X-ray DS by using a state-of-the-art high
As a last step we investigated the relationship between the temperature dependences of the island and matrix Bragg peaks and the DS
Summary
Na0.5Bi0.5TiO3 (NBT) is a ferroelectric material that is interesting both as the foundation of many potential lead-free piezoelectrics (Takenaka et al, 2008) and as a model system for the crystallography of perovskites (Mitchell, 2003). The commonly accepted reference point stems from the seminal neutron powder diffraction study of Jones & Thomas (2002). The mechanism of transition between the structures described by the R3c and P4bm space groups, which lack a group–subgroup relation, remains unexplained
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