Fig. 4: Antiferroelectric order in incommensurately modulated (Na0.65Ag0.20Ca0.15)(Nb0.85Ti0.15)O3.
From: Improper antiferroelectricity in NaNbO3-based perovskites driven by antiferrodistortive modulation
a ADF-STEM image projected along [001]p zone axis. The mirror planes (or “tilt-twin boundaries”) are denoted by vertical dashed lines. b Cation displacement map with respect to the reference lattice derived from (a). Arrows in yellow and cyan show displacement of A and B cations, respectively. c Weight factor map of PCA2 derived from (a) showing incommensurate AFD modulation. The AFD modulation wave can be manifested by the spatial variation of the PCA2 weight factors. d Vertically averaged displacement profiles for A (dA) and B (dB) cations along [100]p extracted from (b). e Vertically averaged weight factor profile extracted from (c). The displacive modulation wave shown in (d) and the AFD modulation revealed in (e) are in quadrature (90° out of phase), signifying the AFD-polar coupling. Error bars indicate ±1 SD.
