Role of charged defects on the electrical and electro-mechanical   properties of rhombohedral Pb(Zr,Ti)O3 with oxygen octahedra tilts
  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. 
Tadej Rojac, Silvo Drnovsek, Andreja Bencan, Barbara Malic, and Dragan   Damjanovic
cond-mat.mtrl-sci