Improved comprehensive properties induced by multi-phase coexistence in KNN ceramics

(1- x ) (K 0.48 Na 0.52 ) (Nb 0.97 Sb 0.03 )O 3 - x (Bi 0.5 Zn 0.25 )ZrO 3 [(1- x ) KNNS - x BZZ] piezoceramics are prepared by traditional solid state method. The phase structure, microstructure, dielectric properties, ferroelectric properties and the piezoelectric properties of KNN piezoceramics are thoroughly investigated. A polymorphic phase boundary (PPB) coexisting with orthorhombic-tetragonal phase (O-T) is formed at 0.01 ≤ x ≤ 0.02 in the ceramics, which is the primary cause of improved piezoelectric properties. Furthermore, the large grain size causes the electric domain within the ceramic easier to deflect, thus resulting in better piezoelectric properties. The best overall properties is obtained at 0.99 KNNS - 0.01 BZZ ( d 33 = 308 pC/N, T C = 334 °C, ε r = 6563) with the PPB, demonstrating that the coexistence of O-T phase plays a positive role in improving the piezoelectric properties of KNN ceramics. This study provides more selectivity for the practical application of piezoelectric ceramics. • A new lead-free piezoelectric material system of KNNS-xBZZ is designed. • The overall performance of KNN is improved by doping to form multiple coexistence. • Large grain size can reduce the electric domain deflection resistance. • Multi-phase coexistence reduces the polarization deflection energy barrier.