Origin of F spots and stress sensitivity in lanthanum lead zirconate titanate

In this study a systematic microstructural characterization of La-modified lead zirconate titanate was carried out by hot- and cold-stage transmission electron microscopy and selected area electron diffraction. The existence of 1/2[111] superlattice reflections (F spots) became evident near 300 degree C on cooling. The intensity of the F spots was found to increase with decreasing temperature, approaching a near constant intensity below 100 degree C. In conjunction with compositional studies, it was proposed that the F spots arise from a doubling of the unit cell associated with a tilting of oxygen octahedra. The presence of F spots at temperatures approaching the onset of local polarization was then interpreted as the existence of a hierarchy of domain states. This hierarchy was proposed to consist of an average-cubic macroscopic structure containing rhombohedral micropolar regions on the scale of 50--100 A that contain ferroelastic microtwins on the scale of several tens of angstroms