摘要：Using electron diffraction, trends in the local structural behaviour of the K𝑥Na1−𝑥NbO3 (KNN x) and the (1 − 𝑥)Na0.5Bi0.5TiO3 +
𝑥BaTiO3 (NBT-(𝑥)BT) systems are investigated. In KNN, electron diffraction shows a single plane of diffuse intensity perpendicular
to [010] across the entire phase diagram, indicating the existence of ferroelectric disorder along this axis. An additional characteristic
pattern of diffuse scattering is also observed, involving rods of diffuse intensity running along the [100]p
∗ and [001]p
∗ directions
of the perovskite substructure and indicative of octahedral tilt disorder about these axes. Similarly, in the NBT-xBT system,
rods of diffuse intensity running along the ⟨100⟩p
∗ directions of the perovskite substructure are observed, again indicating
octahedral tilt disorder. Ferroelectric-like disorder is also observed in highly BT doped samples, and a continuous change from
the “rhombohedral” structure of NBT to the “tetragonal” structure of NBT-12BT is seen from characteristic variation in observed
superstructure reflections. A crystal chemical rationalisation of these results is performed, and the implications for structure and
properties are discussed.
