Temperature dependence of the direct piezoelectric effect in relaxor-ferroelectric single crystals: Intrinsic and extrinsic contributions

The direct piezoelectric response d₃₃ of [001]_C-poled 0.955Pb(Zn_1/3Nb_2/3)O₃–0.045PbTiO₃ [PZN-4.5PT] and 0.98Pb(Zn_1/3Nb_2/3)O₃–0.08PbTiO₃ [PZN-8PT] has been investigated as a function of temperature upon heating above 40 °C to the paraelectric phase. Using a Rayleigh-law based analysis, it is shown that both the reversible/intrinsic and irreversible (extrinsic) contributions to the response increase in both compositions as the phase transition to a tetragonal phase is approached. The latter is likely due to an increased domain wall mobility close to the first order transition temperature, which also gives rise to an increased frequency dispersion. Large reversible direct piezoelectric responses d₃₃≫1600pm/V are observed for both compositions, which increase dramatically close to the transition temperature. Most importantly, the reversible contribution is always much larger than the irreversible part in the low temperature, domain-engineered phase, the latter accounting for around 20% of the response in PZN-8PT, at 40 °C, and 5% in PZN-4.5PT. The importance of this result to the validity of the adaptive phase model is discussed.