Low-frequency dynamics of 0.45PMN-0.55PSN solid solution

Abstract

Lead magnoniobate-scandoniobate (PMN-PSN) solid solutions are important functional materials for transducer/actuator devices due to their extraordinary dielectric and electromechanical properties. These unique properties are related to the unusual low-frequency relaxation dynamics, which has not been sufficiently understood until now. In our paper the low-frequency relaxation dynamics of 0.45Pb(Mg1/3Nb2/3)O3–0.55Pb(Sc1/2Nb1/2)O3 single crystal is studied in frequency range 10 mHz–1 MHz at temperatures near the dielectric permittivity maximum. Four relaxation processes are identified. Low-frequency mode demonstrating the critical divergence around 306 K is revealed. However, the phase transition into ferroelectric phase at this temperature does not occur. Near 306 K, the appearance of M-type superstructure is found related to the combination of oxygen octahedral rotation and anti-parallel shifts of lead ions. The appearance of the additional order parameter suppresses the slowing down of the ferroelectric mode and the phase transition into the ferroelectric phase occurs only below 295 K. In addition, two relaxation processes, similar to reorientation and “breathing” polar nanoregion (PNR) modes reported for PMN, are found. The sharp softening of “reorientation mode” is observed on cooling from 315 to 295 K with Tf ∼288 K. The fourth relaxation process is the Debye process, and we assume that it is associated with defects relaxation. Below 295 K, all four relaxation processes still exist, but their parameters are practically temperature independent. The low-temperature phase is not exactly a “normal” ferroelectric phase, the PNRs persist in the FE phase.