Although
multiphase coexistence endows potassium sodium niobate
(KNN)-based ceramics with enhanced piezoelectric properties and promising
potential in electronic devices, the physical mechanisms are still
left way far behind. In this paper, (1–x)K0.48Na0.52Nb0.95Sb0.05O3–x(Bi0.5Ag0.5)(Zr0.9Hf0.1)O3 ceramics were selected
as an example to probe the physical mechanisms. By tailoring the x value, a diffused rhombohedral–orthorhombic–tetragonal
(R–O–T) coexistence was obtained at x = 0.04, affording a large piezoelectric coefficient d33 of 510 pC/N and a high Curie temperature Tc of 219 °C. The piezoelectricity enhancement mainly
originated from the enhanced dielectric response and abundant submicron
striped domains (50–100 nm) consisting of hierarchic nanodomains
(10–15 nm). Importantly, although the diffused R–O–T
multiphase coexistence exhibited facilitated domain switching, it
was also bothered by reduced effectively reoriented domains and increased
back-switching of already reoriented domains. Therefore, understanding
the related physical mechanism is helpful to the further design of
high-performance KNN-based ceramics used for electronic devices.