The impact of chemical heterogeneity in lead-free (K, Na)NbO3 piezoelectric perovskite: Ferroelectric phase coexistence

(K, Na)NbO3 (KNN)-based solid solutions are outstanding lead-free piezoelectric materials, yet stable reproduction of these materials has always been an obstacle. In the present study, significant ferroelectric phase coexistence was observed in the polycrystalline ceramic sample after sintering. The ferroelectric phase coexistence can be well explained by the chemical heterogeneity in the calcined powder, which is a consequence of using monoclinic Nb2O5 as the precursor. It was demonstrated that the ferroelectric phase coexistence, as well as the chemical heterogeneity, could be a barrier of the reproducibility of performances. Therefore, we suggest that extra attention should be paid on the processing of KNN-based materials, from the very beginning, that is, the choice of precursors.