Ferroelectrics under the Synchrotron Light: A Review

Abstract

Currently, an intensive search for high-performance lead-free ferroelectric materials is taking place. ABO3 perovskites (A = Ba, Bi, Ca, K and Na; B = Fe, Nb, Ti, and Zr) appear as promising candidates. Understanding the structure–function relationship is mandatory, and, in this field, the roles of long- and short-range crystal orders and interactions are decisive. In this review, recent advances in the global and local characterization of ferroelectric materials by synchrotron light diffraction, scattering and absorption are analyzed. Single- and poly-crystal synchrotron diffraction studies allow high-resolution investigations regarding the long-range average position of ions and subtle global symmetry break-downs. Ferroelectric materials, under the action of electric fields, undergo crystal symmetry, crystallite/domain orientation distribution and strain condition transformations. Methodological aspects of monitoring these processes are discussed. Two-dimensional diffraction clarify larger scale ordering: polycrystal texture is measured from the intensities distribution along the Debye rings. Local order is investigated by diffuse scattering (DS) and X-ray absorption fine structure (XAFS) experiments. DS provides information about thermal, chemical and displacive low-dimensional disorders. XAFS investigation of ferroelectrics reveals local B-cation off-centering and oxidation state. This technique has the advantage of being element-selective. Representative reports of the mentioned studies are described.

Piezoelectric Ceramics of the (1 − x)Bi0.50Na0.50TiO3–xBa0.90Ca0.10TiO3 Lead-Free Solid Solution: Chemical Shift of the Morphotropic Phase Boundary, a Case Study for x = 0.06

“…The fraction of the ferroelectric R3c symmetry in BNBT6 ceramics increases after application of an electric field at the expense of the Pm-3m cubic symmetry [31]. That is, the short-range polar order (nanodomains) of the globally non-polar component of the material becomes a long-range polar order (macroscopic ferroelectric domains) under the action of the electric field.…”

“…However, the coexistence of ferroelectric rhombohedral R3c and ferroelectric tetragonal P4mm is well documented at the tetragonal edge of the 0.08 < x < 0.11 [15]. Besides, the wide peaks at the low-angle side of the strong perovskite peaks (marked with arrows in Figure 6) disappear after powdering the poled samples, thus indicating that this is a structural feature related to a surface structure [31] but not to the coexistence of ferroelectric phases.…”

“…In Figure 6 we can see that the three mentioned features observed at XRD patterns of BNBT6 sol-gel autocombustion ceramics [27,31], are not observed in all samples. Specifically, the wide peaks associated with a surface structure [27,31,32,33] are only observed in most of the ceramics prepared by the Pechini route (marked with arrows).…”

Characterization of Pb-Free KNbO3- and (Na,Bi)TiO3-Based Piezoelectric Single-Crystals Using X-ray and Neutron Diffraction

“…Indeed, advanced diffraction experiments on polycrystalline ceramics have elucidated several electric field and/or stress-induced structural mechanisms that are unique to Pb-free piezoelectrics. A review of these developments can be found in references [41,42]. Nevertheless, similar reviews on single-crystal diffraction experiments of Pb-free piezoelectrics are absent.…”

“…The crystallographic structural changes can be characterized from data collected in a diffraction experiment by monitoring changes in some essential features, such as hkl diffraction peak position to determine changes in lattice planes spacing and splitting of hkl reflections to identify changes in crystallographic symmetry. In addition, change in intensities of hkl reflections can reflect various crystallographic and microstructural changes such as relative positions of different ions, state of microstructural defects, as well as internal strains, which can be distinguished based on quantitative modeling [36,37,[41][42][43][44].…”