Abstract
Lead-based relaxor ferroelectrics are key functional materials indispensable for the production of multilayer ceramic capacitors and piezoelectric transducers. Currently there are strong efforts to develop novel environmentally benign lead-free relaxor materials. The structural origins of the relaxor state and the role of composition modifications in these lead-free materials are still not well understood.
In recent years solid-state NMR spectroscopy, combined with quantum-chemical modelling, is evolving into a key technique for the investigation of these important materials. In the first part of the talk we give a brief introduction into the relevant techniques of solid-state NMR spectroscopy.
Next we demonstrate how these techniques were employed to tackle thepreviously unsolved question on the structure of relaxor ferroelectrics at the atomic level by characterizing lead-free piezoceramic solid solutions (100-x)(Bi1/2Na1/2)TiO3-xBaTiO3(BNT-xBT) (for x=1,4,6, and 15). Based on the relative intensity between spectral components in quadrupolar perturbed 23Na Nuclear Magnetic Resonance (NMR), we present direct evidence of the coexistence of cubic and polar local symmetries in these relaxor ferroelectrics. In addition to that, we demonstrate how the cubic phase vanishes whenever a ferroelectric state is induced, either by field-cooling or changing dopant amount, supporting the relation between this cubic phase and the relaxor state.
In the next step the spectral properties of the non-cubic portions are studied in detail. For the first time it is shown that the peculiar composition dependence of the EFG distribution width (ΔQISwidth) correlates strongly to the dispersion in dielectric permittivity, a fingerprint of the relaxor state. Significant disorder is found in the local structure of BNT-xBT, as indicated by the analysis of the electric field gradient (EFG) in 23Na 3QMAS NMR spectra.
Finally an outlook and some first preliminary results on other classesof lead-free materialsare presented.

Buntkowsky_CV_2016.pdf