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The study of PSN-PT ferroelectric relaxor ceramics exhibiting extreme values of some physical parameters near the morphotropic phase boundary is reported. The results are discussed to account for the relaxor properties related to defects and disordering of the PSN-PT system.

The growing interest in disordered relaxor ferroelectrics is due to unusual properties mainly related to the existence of broad phase transitions characteristic to the systems. The effects of bias field on the dielectric response and polarisation switching are studied in the 0.5 PbNi 1/3 Nb 2/3 O 3 – x PbTiO 3 –(0.5− x ) PbZrO 3 system at different PbTiO 3 :PbZrO 3 ratio. Thermal behaviour of normalised remnant polarisation P r / P max of compositions with content of lead titanate x =0.33 and x =0.35 at frequency 0.1 Hz and different values of field E o are measured. Results of measured polarisation and depolarisation currents are compared with characteristics of polarisation switching. In the case of composition with x =0.33 the value of P r / P max does not depend on the field amplitude in the range 4–10 kV/cm within the thermal interval from 50 to 135 °C. In composition with x =0.35 the interval of P r / P max independent of E o (5–10 kV/cm) is observed closer to the temperature of dielectric permittivity maximum T m ≈180 °C

The growing interest in disordered relaxor ferroelectrics is due to unusual properties mainly related to the existence of broad phase transitions, which are characteristic to the systems. The effects of bias field on the dielectric response and polarisation switching are studied in the 0.5PNN-xPT-(0.5-x)PZ system at different PT:PZ ratio. Thermal behaviour of normalised remnant polarisation P r /P max of compositions with lead titanate content x = 0.33 and x = 0.35 at frequency 0.1 Hz and different values of field E o are measured. In these compositions independent ranges of field amplitude was determined. Results of measured polarisation and depolarisation currents are compared with characteristics of polarisation switching.

Reversible dielectric permeability l ' r (E = ) of 0.5PbNi 1/3 Nb 2/3 O 3 - 0.5Pb(Zr,Ti)O 3 ferroelectric ceramics is studied at different lead titanate to zirconate ratios. Particular features of dielectric response - fractures and small plateaux on the l ' r (E = ) curve are observed at some values of the bias field E = . The anomalies are explained by phase transformations induced by applied field and suggest of broadening of the morphotropic phase boundary in the system.

Lead titanate solid solutions exhibits extreme values of some physical parameters. We have investigated a ferroelectric relaxor ceramics of PSN-PT composition near the morphotropic phase boundary. Results are discussed with account for the relaxor properties related to defects and disordering of the PSN-PT system.

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