Phase transition behavior and high electrostrictive strains in Bi(Li_0.5Nb_0.5)O₃-doped lead magnesium niobate-based solid solutions

Bi(Li_0.5Nb_0.5)O₃ (BLN) was adopted to tailor the Curie temperature (T_C) and the resulting ferroelectric and electrostrictive properties of solid solutions of the morphotropic phase boundary relaxor ferroelectric 0.67 Pb(Mg_1/3Nb_2/3)O₃-0.33PbTiO₃ (0.67PMN-0.33 PT). The ceramic samples were synthesized by a solid reaction method, and the BLN content was set to 2.5 at.%, 5 at.%, 7.5 at.%, and 10 at.%. X-ray diffraction results suggested that BLN cannot enter the 0.67PMN-0.33 PT crystal lattice completely, resulting in the formation of a second phase (Pb₂Ti₂O₆ with pyrochlore structure) in all the samples. With increasing BLN content, a decrease in T_C and a ferroelectric-to-relaxor transition were revealed by the dielectric and ferroelectric properties. High electric-field-induced strains of 0.167%–0.228% with low hysteresis (<7%) were observed in the samples. Most importantly, an almost purely electrostrictive strain of 0.184% with ultralow hysteresis (<2%) was obtained in the 7.5 at.% BLN-doped sample. The thermal stability of the strains in the bipolar and unipolar modes were evaluated from 30 to 120 °C. The longitudinal electrostrictive coefficient Q₃₃ ranged from 0.150 to 0.185 m⁴/C² and was insensitive to temperature. Our results suggest that BLN-doped 0.67PMN-0.33 PT ceramics could have potential applications in actuator devices owing to their high strain response and ultralow hysteresis.