Electrical after-effects in Pb(Ti, Zr)O3 ceramics

Abstract

Pb(Ti, Zr)O3 ceramics doped with Al, Mn or Fe exhibit constricted or asymmetrically displaced hysteresis loops. This distortion is due to an internal bias field Ei which can exceed the coercive field strength. Ei depends on the Ti/Zr ratio and on the kind of dope, and it increases with increasing doping concentration.After repeated cycling of the hysteresis loop the distortion disappears. This process, called “hysteresis relaxation,” obeys a time law of the form Ei(t) ∼exp(-t/τ)and is found to behave both like a field and thermally activated process. The activation energy of all investigated specimens doped with transition metal ions (Mn, Fe) lies between 0.6 and 0.7 eV, that of Al-doped samples is about 0.8 eV.Comparison of the behaviour of the dielectric and mechanical losses with that of the internal bias shows that these effects are closely correlated. From this correlation some conclusions can be drawn concerning the nature of Ei, the physical causes of the observed after-effects, and the influence of the kind of dope on the losses.Al-doped Pb(Ti, Zr)O3 ceramics exhibit an intergranular second phase which collects space charges during aging. The resulting space charge field is equivalent to an internal bias field which impresses an overall preferred direction of polarization on each crystallite.Fe and Mn are incorporated into the lattice. The resulting defects can either act as pinning points for the domain walls or give rise to anisotropic centres which favour a certain direction of polarization. This in turn stabilizes the domain configuration and reveals itself experimentally as an internal bias field.