Abstract
•Unveiling the effects of the K/Na ratio on PBE-featured KNN-based ceramics from multiscale view.•Observing the local stress heterogeneity in Na+ rich side and the local polar heterogeneity in K+ side.•Unraveling the role of the coupling between the local stress heterogeneity and the polar heterogeneity in piezoelectric properties and the temperature stability.
Although vast efforts have been given to the phase boundary engineering (PBE) of potassium sodium niobate (KNN) ceramics by using chemical dopants, the inherent issues like the K/Na ratio were not paid enough attention, hindering the further understanding of physical mechanisms. Herein, we investigated the effect of the K/Na ratio on PBE-featured KNN-based ceramics. The K/Na ratio significantly influences the local A-site environment and thereby alters mesoscopic ferroelectric domains and macroscopic structure and performance. A much higher Na+ content results in the local stress heterogeneity, while a much higher K+ content brings in the local polar heterogeneity. Due to the appropriate coupling between the local stress and the polar heterogeneity, piezoelectric properties and the temperature stability of electro-strain are optimized on the Na-rich side. Therefore, beyond seeking appropriate chemical dopants, elaborately tailoring the K/Na ratio is also important for further improving the piezoelectric properties of PBE-featured KNN-based ceramics.