Structure instability-induced high dielectric properties in001-oriented 0.68Pb(Mg_1/3Nb_2/3)O₃-0.33PbTiO₃ crystals

The structure evolution and origin of ultrahigh dielectric properties have been investigated in the low temperature range from 300 K to 5 K for001-oriented 0.68Pb(Mg_1/3Nb_2/3)O₃-0.33PbTiO₃ (PMN-33PT) crystal. The experimental results reveal that a short-range ordered monoclinic M_A is the dominant phase at ambient temperature. As the temperature drops below 270 K, the M_A transforms into monoclinic M_C, and the M_C remains stable until 5 K. Although no phase transition occurs from 5 K to 245 K, polar nanoregions (PNRs) display visible changes. The instability of PNRs is suggested as responsible for the low temperature relaxation. The ultrahigh dielectric constant at room temperature is associated with the instability of local structure and phase transition. Our research provides an insight into the design of high-performance ferroelectric materials.