Tuning the Covalency of A–O Bonds to Improve the Performance of KNN-Based Ceramics with Multiphase Coexistence

Abstract

Although a room-temperature multiphase coexistence (MPC) strategy improves the piezoelectric coefficient (d33) of potassium sodium niobate ((K, Na)NbO3, KNN) ceramics, it still suffers from the dependencies on composition and temperature, making it remain challenging to further improve d33 and temperature stability of strain for an already-built MPC. Here we proposed a new route to resolve this issue, that is, tuning the covalency of A-O bonds in an already-built MPC. We chose 0.96(Na0.60K0.40)(Nb0.955Sb0.045)O3-0.04(Bi0.5Na0.5)ZrO3 ceramics as an already-built MPC and replaced (Bi0.5Na0.5) 2+ with Ba 2+ to tune the covalency of A-O bonds. Thus, we synthesized 0.96(Na0.60K0.40)(Nb0.955Sb0.045)O3-0.04(Bi0.5Na0.5)1-xBaxZrO3 ceramics. We not only improved d33 values from 450 pC/N (at x=0) to 500-505 pC/N (at x=0.05-0.10) but also obtained the enhanced temperature stability for strain at x=0.10, outperforming that of samples with x=0 and other KNNbased ceramics. The increased d33 is attributed to the well-preserved MPC and the repaired long-range ordering (LRO), and the improved temperature stability of strain is due to shifting the MPC to a slightly higher temperature than room temperature. Therefore, the new route is useful to further improve the 2 performance of an already-built MPC, benefitting to the future design of MPC and the practical application of KNN-based ceramics.

Meticulously tailoring phase boundary in KNN‐based ceramics to enhance piezoelectricity and temperature stability

“…The component (Bi 0.5 Na 0.5 )ZrO 3 (BNZ) and antimony (Sb) element is used to tune phase transition temperatures to room temperature, which is effective to construct MPC in KNN ceramics 9,10 . Due to the strong hybridization between Bi 6p and O 2p orbitals, Bi is essential for reducing T O–T value and stabilizing the tetragonal phase because it prefers to forming BiO 4 configuration at A‐site and thus induces the [0 0 1] off‐center displacement 11,12 . Inspired by the aforementioned idea, it is certain that slightly replacing Bi content with other ions can suppress the formation of T phase and regulate MPC critically.…”

“…9,10 Due to the strong hybridization between Bi 6p and O 2p orbitals, Bi is essential for reducing T O-T value and stabilizing the tetragonal phase because it prefers to forming BiO 4 configuration at A-site and thus induces the [0 0 1] off-center displacement. 11,12 Inspired by the aforementioned idea, it is certain that slightly replacing Bi content with other ions can suppress the formation of T phase and regulate MPC critically. This strategy is therefore to move the ferroelectric phase transition toward a higher temperature above room temperature and make piezoelectricity not monotonously decline with rising temperature, which is in favor of good thermal stability within the operating temperature range.…”

Pressure- and Temperature-Induced Structural Phase Diagram of Lead-Free (K0.5Na0.5)NbO3–0.05LiNbO3 Single Crystals: Raman Scattering and Infrared Study

“…It is necessary to find the relationships between the lattice symmetry, structure evolution, and KNN-based ferroelectric performances with MPB composition, which can 22−24 In general, the phase boundary in KNN crystals can be regarded as the intrinsic features of polymorphic phase transition (PPT), which can shift to room temperature by adjusting element doping. 25,26 Li + substitution has been studied in depth to construct the O-T phase boundary. 27,28 Moreover, as a comprehensive and useful additive, the Mn ions in MnO 2 have different valence states (+2, +3, and +4).…”

“…Since the first exploration of the phase boundary of KNN-based ceramics in 2004, excellent piezoelectric properties have been continuously obtained in KNN with an O-T phase boundary. Various studies on the O-T phase boundary have accumulated rich experience on how to select effective potential additives for KNN. − In general, the phase boundary in KNN crystals can be regarded as the intrinsic features of polymorphic phase transition (PPT), which can shift to room temperature by adjusting element doping. , Li + substitution has been studied in depth to construct the O-T phase boundary. , Moreover, as a comprehensive and useful additive, the Mn ions in MnO 2 have different valence states (+2, +3, and +4). , On the other hand, the single crystal has leakage current on account of the presence of lattice defects. , Low leakage current and the additional high antifatigue properties in Mn-doped KNN crystals were obtained in recent work . In the condition of KNN-LN doped with MnO 2 , Mn ions substitute A or B sites as electron or hole absorber during oxidation .…”

Comparison of contribution to phase boundary from A-site aliovalent dopants in high-performance KNN-based ceramics

“…For example, the O-T phase boundary was capable of enhancing the piezoelectric constant (d 33 ) to 416 pC N À1 in textured KNNbased ceramics, 7 while higher values of 490-680 pC N À1 and 700 pC N À1 are respectively achieved in conditional and textured KNN-based ceramics with multiphase coexistence of rhombohedral-tetragonal (R-T) or rhombohedral-orthorhombic-tetragonal (R-O-T) phases. [8][9][10][11][12] In recent years, based on the significant contribution of phase boundaries, their deep understanding has gradually increased to further adjust their structure and optimal performance, such as relaxor behavior around the phase boundary, 10,[13][14][15][16] the domain structure of different phase boundaries, 9,[16][17][18][19] the intrinsic and extrinsic contribution based on the phase boundary, 19,20 and dopant impact on multi-layered structures, [21][22][23] etc. Notably, the effective strategy of shifting phase transition temperatures (T R-O and T O-T ) to format new phase boundaries (R-T and R-O-T) has been widely utilized to achieve high piezoelectric properties.…”