Abstract
Great progress in the field of piezoelectricity of (K,Na)NbO3 (KNN) lead-free ceramics, driven by emerging rhombohedral-tetragonal (R-T) phase boundary, has instigated research activity regarding elaborate controls of the phase boundary structure. Through phase-microstructure-property mapping in KNN ceramics doped with Bi-containing perovskite oxides, in this study we for the first time report the existence of a certain R-T phase boundary state by which to create maximum piezoelectric response in KNN systems. This phase boundary condition is usually comprised of approximately 15% R phase and 85% T phase, regardless of the choice of dopant material. Any deviation from this phase composition, either by inclusion of orthorhombic (O) phase or by enrichment of R phase, has a negative effect on the value of d33. These findings can provide useful guidance for chemical doping control associated with the type of phase boundary and the phase composition for advanced KNN-based materials.
Highlights
A great deal of effort is being expended to develop viable and competitive lead-free piezoelectric materials
The highest d33 value (570 pC/N) reported to date among the randomly-oriented KNN-based ceramics is achieved by constructing a R-T phase boundary by doping with Sb5+, BaZrO3 and (Bi,K) HfO310
Even though the current upsurge of research interest has focused on these emerging phase boundaries, little is known about the exact role of ferroelectric R, O, and T phases or their coexistence constructing a phase boundary in piezoelectricity
Summary
According to recent in-situ synchrotron XRD work, there is a close relationship between an electric-induced phase transition and the piezoelectricity of KNN ceramics[13,29,30,31]; the enhanced piezoelectricity achieved by a T-rich R-T phase boundary is attributed to the more positive role of the irreversible tetragonal-electric induced phase transition compared to the rhombohedral-electric induced phase transition with a certain degree of reversibility[13] It has been confirmed via Rayleigh analysis (Fig. S7a–c) that the intrinsic (lattice distortion or reversible domain wall vibration) and extrinsic (irreversible motion of domain wall or phase boundaries) contributions to piezoelectric activity are highest at optimum R-T phase composition. When the ceramics possess an R-T phase boundary with more than 15% of R, doping control is no longer effective because further doping will certainly induce a R-richer phase boundary, accompanied by decreased grain sizes, with poor piezoelectric performance
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
