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The dielectric response of hard (Fe-doped) and soft (Nb-doped) rhombohedralPb(Zr0.58Ti0.42)1-xMexO3 (PZT; Me= Fe or Nb) ceramics was studied atsubswitching conditions over a wide range of temperatures (50 C to 450 C) andfrequencies (10 mHz to 10 kHz). The results show qualitative differences inbehavior of the acceptor and donor doped samples. Hard materials exhibit asteep increase of the complex permittivity with decreasing frequency. The onsetof the dispersion is thermally activated with activation energy of about0.6-0.8 eV and is attributed here to oxygen vacancy hopping. Activation energyfor ac conductivity observed in soft materials is estimated to about 1.7 eV,corresponding to the half of the energy gap of Pb(Zr,Ti)O3 and is thusconsistent with electronic conduction. The relevance of ionic hoppingconductivity in hard materials to ferroelectric aging / deaging and hardeningis analyzed. Strong ionic conductivity in hard and its absence in soft samplesagree well with the dipolar mechanism of ageing in hard materials and theabsence of significant ageing in soft materials.

Charge migration in Pb(Zr,Ti)O3 ceramics and its relation to ageing, hardening and softening