  Oxygen octahedra tilting is a common structural phenomenon in perovskites and
has been subject of intensive studies, particularly in rhombohedral Pb(Zr,Ti)O3
(PZT). Early reports suggest that the tilted octahedra may strongly affect the
domain switching behavior, dielectric and piezoelectric properties of PZT
ceramics. In a way similar to that proposed for tilts, however, charged
defects, associated with oxygen vacancies, may also inhibit the motion of the
domain walls, resulting macroscopically in pinched hysteresis loops and reduced
piezoelectric response. Here, we revisit the early studies on rhombohedral PZT
ceramics with tilted octahedra by considering a possible role of both tilts and
charged defects on domain-wall motion. We show that the observed pinched
hysteresis loops are likely associated with the presence of defect complexes
containing charged oxygen vacancies, and not tilts as suggested in some cases.
Regardless of the presence or absence of long-range ordered tilts in
rhombohedral PZT, the effect of charged defects is also prominent in weak-field
permittivity and piezoelectric properties, particularly at sub-Hz driving
conditions where the conductivity, related to the motion of oxygen vacancies,
gives rise to strong frequency dispersion.
