Relaxor ferroelectrics are chemically modified ferroelectric materials that are structurally disordered at different length scales depending on the nature of the substitution ion. Relaxor ferroelectrics are attractive for energy storage applications because of their slim polarization-electric field hysteresis loops that leads to high recoverable energy density, in contrast to nominal ferroelectric materials. Relaxor state is simply facilitated by disruption of the spatial long-range correlation of B-site displacements in barium titanate based systems. Such lattice disruption can occur on the basis of difference in the ionic radii and/or the valance states of the substituting ion. A larger ionic radius of the substituting ion can induce strain fields hindering B-site displacements, disrupting the ferroelectric order. On the other hand, a different valence state can introduce an added complexity by triggering different charge compensation schemes to maintain lattice electroneutrality. In such case, the disruption of B-site correlation is attained in form of a ferroelectric domain pinning mechanism. In this work, Raman spectroscopy is used to elucidate the short-range mechanisms disrupting ferroelectricity in such complex compositionally graded materials. We demonstrate here new experimental methods and interpretations to Raman spectra of structurally disordered relaxor ferroelectric ceramics. A new theoretical procedure and a combined experimental-theoretical approach to study defect chemistry of barium titanate based relaxors are attempted. The role of localized random fields from substitutional defects on the lattice disorder is further studied using various dielectric and spectroscopic methods to complement the observation from Raman scattering. Finally, evidence to lattice defects stabilizing short polar order in the non-polar phase of nominal FE systems are reported, as testified by the appearance of forbidden Raman modes in the cubic symmetry for barium titanate and in substituted barium titanate materials. The knowledge gained here on the local chemical environment and lattice disorder by studying the local structure and lattice dynamics can improve the understanding of the role of different substitutions and/or defects on macroscopic material properties in perovskite ferroelectrics. Such understanding can then be translated to designing new material systems for various applications (e.g. energy storage or piezoelectric) that are efficient as well as environmentally friendly.
|Translated title of the contribution||Raman Spektroskopie von Bariumtitanat basierten Relaxor-Ferroelektrika|
|Publication status||Published - 2021|
Bibliographical noteembargoed until 15-03-2022
- Raman spectroscopy
- Barium titanate
- Relaxor Ferroelectrics
- Lead-free relaxors