Hui Ding (Düsseldorf / DE), Sonja Egert (St Andrews / GB), Bin-Xiang Huang (Darmstadt / DE), Andreas Klein (Darmstadt / DE), Gerd Buntkowsky (Darmstadt / DE), Hans-Joachim Kleebe (Darmstadt / DE), Leopoldo Molina-Luna (Darmstadt / DE)
Abstract text (incl. figure legends and references)
The classical model of the prototype antiferroelectric material PbZrO3 with antiparallel pairs of Pb displacements of equal magnitude has long been considered a principal guide for the understanding of antiferroelectricity. However, this simplistic picture has raised great concern as it is yet to be found in a real material, and a detailed examination of the 3-dimensional Pb positions is still lacking.
Here, not only the in-plane displacement but also the out-of-plane environment of Pb in PbZrO3 and (Pb,La)(Zr,Sn,Ti)O3 (PLZST) perovskite oxides is considered by jointly employing high-resolution scanning transmission electron microscopy (HRSTEM) and solid-state nuclear magnetic resonance (NMR) spectroscopy.
Displacement studies of PbZrO3 using the high-angle annular dark-field (HAADF) technique revealed an ordered four-fold modulation, which consists of two distinct segments that are nearly perpendicular to each other, contrasting the Kittel model. This ordered in-plane configuration is complemented by two discrete 207Pb NMR signals reflecting alternating displacement magnitudes out-of-plane. On the other hand, PLZST is characterized by an inhomogeneous distribution of the Pb displacement modulation layers and Pb-O bond width calculated from annular bright-field (ABF) image, further manifested by a distribution of 207Pb resonance frequencies revealing a significant increase in the displacement distribution width.
The combination of TEM and NMR techniques allows for a complementary exploration of the 3-dimensional crystal structure, correlating the microstructural displacements with the bulk displacement distribution both qualitatively and quantitatively. The findings rationalize our understanding of the complex polarization configuration in PbZrO3-based antiferroelectrics that go beyond the Kittel model and highlight their highly disordered nature instead.