The effects of the phase structure of the polymorphic phase boundary on the piezoelectric properties of (K,Na)NbO3-based ceramics

• Effect of R, O, and T phases on piezoelectric property of KNN-based ceramics was investigated.
• Formation of R-T phase boundary by O phase shrinkage enhances piezoelectric performance.
• Enrichment of T phase in R-T phase boundary negatively affects piezoelectric activity.
• Electrical poling on piezoelectric property strongly depends on nature of phase boundary.

We report the effects of the phase, i.e., the rhombohedral (R), orthorhombic (O) and tetragonal (T) phase, within a polymorphic phase boundary on the piezoelectric properties of (K,Na)NbO3 ceramics doped with Bi(Na,K,Li)ZrO3 and (Bi,Na)TiO3. For the R-O-T phase boundary, the formation of an R-T phase boundary by O phase shrinkage is clearly beneficial to enhance the piezoelectric performance, whereas the enrichment of the T phase in the R-T phase boundary negatively affects the piezoelectric activity. Electrical poling in relation to the piezoelectric property strongly depends on the nature of the phase boundary, requiring the optimization of temperatures corresponding to the R-T phase boundary without the O phase.