Non-equivalent ionic dopants and their impacts on properties of potassium sodium niobate-based lead-free ceramics

In the work, (1-x) (K0.48Na0.52) (Nb0.96Sb0.04)O3-x(Bi0.5K0.5)0.7Ca0.3ZrO3 [(1-x)KNNS-xBKCZ] lead-free piezoceramics are prepared to investigate location and associated impacts of non-equivalent ionic dopants on phase transition and property enhancement. Results of XRD refinement and analysis of transmission electron microscopes (TEM) strongly prove that Rhombohedral-Tetragonal (R-O-T) phase coexistence for 0 ≤ x ≤ 0.04. According to lattice parameters, R phase should be ascribed to lattice deformation subjected to shear stress owing to the cooperation of multiple ionic dopants in A sites and B sites. Based on the variation of temperature-dependent capacitances with the frequencies and atomic-resolution HR-O-TEM image, much more oxygen vacancies are investigated because of major substitution of Ca2+ in B site, which leads to an obvious decrease of TC in (1-x)KNNS-xBKCZ besides c/a of O phase. Additionally, domain wall motion is demonstrated to become easier through calculating intrinsic piezoelectric response using Rayleigh law and consequently, piezoelectric properties of (1-x)KNNS-xBKCZ are greatly enhanced (d33∼440 pC/N and d*33-500 pm/V) in R-O-T phase coexistence region.