Ferroelectric-to-relaxor transition and ultrahigh electrostrictive effect in Sm³⁺-doped Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ ferroelectrics ceramics

Rare-earth Sm³⁺-doped Pb(Mg_1/3Nb_2/3)O₃–0.25PbTiO₃ (PMN-0.25PT) ferroelectric ceramics with doping amounts between 0%–3% were developed via a conventional solid-state method. The doping effect of Sm³⁺ ions on the PMN-0.25PT matrix was systematically investigated on the basis of the phase structure, temperature-dependent dielectric, ferroelectric, and electrotechnical properties. Due to the disruption of long-range ferroelectric order, the addition of Sm³⁺ ions effectively lowers the T_m (temperature corresponding to maximum permittivity) of the samples, leading to enhanced relaxor ferroelectric (RFE) characteristic and superior electric field-induced strain (electrostrain) properties at room temperature. Intriguingly, a considerable large-signal equivalent piezoelectric coefficient d₃₃^* of 2376 pm/V and a very small hysteresis were attained in the PMN-0.25PT component doped with 2.5 mol.% Sm³⁺. The findings of piezoelectric force microscopy indicate that the addition of Sm³⁺ increases the local structural heterogeneity of the PMN-0.25PT matrix and that the enhanced electromechanical performance is due to the dynamic behavior of polar nanoregions. Importantly, strong temperature-dependent electrostrain and electrostrictive coefficient Q₃₃ are observed in the critical region around T_m in all Sm³⁺-modified PMN-0.25PT ceramic samples studied. This work elucidates the phase transition behavior of Sm³⁺-doped PMN-0.25PT and reveals a critical region where electrostrictive properties can be greatly improved due to a strong temperature-dependent characteristic.