Complex impedance studies of the precipitation-hardened lithium sodium niobate ferroelectrics

Precipitation hardening has been demonstrated as a good practice to suppress domain wall mobility and reduce losses in piezoceramics, especially when subjected to high-power drive. The hardening effect is generally determined by the morphology of precipitates introduced during the high-temperature aging treatment. In the present work, impedance spectroscopy is performed on the as-quenched and aged (Li, Na)NbO3 (LNN) solid solution to clarify the influence of aging treatment on the conductivity and electrical heterogeneity of LNN samples. The as-quenched LNN sample shows a lower resistivity due to higher oxygen vacancy concentration, which can be largely eliminated by reoxidation during the aging process. Moreover, the LiNbO3 (LN) precipitate-caused electrical heterogeneity is clarified by analyses of the impedance spectra fitted by an equivalent circuit and the activation energy calculated from relaxation peaks. The revealed impedance changes provide a foundation for future optimization strategies of precipitation-hardened piezoelectric ceramics.