Defect engineering electrical properties of lead‐free potassium sodium niobate‐based ceramics

Abstract

Defect engineering plays an important role in property modification for piezoelectric materials. In this work, we pay much attention to the effect of Nb nonstoichiometry on structure and properties of typical 0.95(K0.45Na0.55)Nb1+xO3–0.05Bi0.5Na0.5HfO3 ceramics. Large piezoelectric constant (d33 ~ 425 pC/N and d33∗ ~482 pm/V) together with high Curie temperature (TC ~ 315°C) have been achieved in the ceramics with excess Nb content (x = 0.01). However, the ceramics with deficient Nb element have seriously suppressed cryogenic εr‐T curves and deteriorated electrical properties. Multi‐scale characterizations including phase structure, microstructure, defect structure and domain structure have been adopted to explain the corresponding phenomenon. Defect complex VNb″″′-VnormalO·· caused by deficient Nb induces clamped domain wall motion, leading to blocked polarization vector and poor electrical properties. On the contrary, the enhanced properties for the ceramics with excess Nb are attributed to easier domain switching due to the suppressed vacancies. We believe that defect engineering, for example nonstoichiometry, cannot only modulate electrical properties but also help us to understand some fundamental and critical problems about KNN‐based ceramics.

Optimizing Output Power Density in Lead-Free Energy-Harvesting Piezoceramics with an Entropy-Increasing Polymorphic Phase Transition Structure

“…With the increased incorporation of atomic species, the symmetry of the system decreases, and the lattice will inevitably become distorted because the interactions between the different atoms cause the bond lengths to increase or shorten. 34,35 The tetragonality (c/a) can reflect the distortion of the KNN-based ceramics 36 and the c/a characteristics of the three systems increased with increasing ΔS conf (Figure 2(g)), confirming that the entropy-increasing PPT structure has a greater tetragonal distortion (see the inset of Figure 2(g)). In addition, the average ionic size difference (δ) is the parameter that is most commonly used to describe the lattice distortion of the high-entropy phase, and the δ of the B-site can be calculated as 22 i k j j j j j j j j y…”

Mechanochemical Synthesis of Orthorhombic Nickel Niobate (NiNb2O6) as a Robust and Fast Charging Anode Material for Lithium-Ion Batteries

“…This may have resulted from oxygen vacancies that form from highly distorted NbO 6 octahedra. , The existence of a lower valence state of transition metal ionsin this case, Nb 4+ has also been related to electron polaron formation, which causes irregularities in the dielectric properties of a material, as described in several literature studies. − Figure c shows two peaks in the spectra for the O 1s orbital, corresponding to lattice O 2– in the M–O bond (M = Ni and/or Nb) and O adsorbed at 531.0 and 534.0 eV, respectively. The binding energies of Ni–O and Nb–O range between 529 and 531 eV, , and thus, it cannot be specified in the XPS analysis. The O adsorbed could be assigned to weakly adsorbed water or other hydroxyl-containing compounds on the surface. , …”

“…After lithiation and delithiation, a peak that corresponds to ROCO 2 Li located around 534–535 eV was detected, which reinforces the idea of SEI layer formation and partial decomposition as its intensity decreases after charge. Another peak located at about 531 eV corresponds to M–O (M = Ni and/or Nb) , and is present in all three stages, with only a slight increase in binding energy after charge (delithiation). Last, the C 1s XPS spectra in Figure f show various C-containing groups and compounds.…”

Superior Electromechanical Compatibility in Lead-Free Piezoceramics with Mobile Transition-Metal Defects

“…Defect engineering, especially the introduction of point defects, is a well-established strategy to manipulate the relevant properties in KNN. ,− At a macroscopic level, defects in piezoelectrics are highly influential to specific properties, either in a positive or negative manner . For example, donor doping or the inclusion of certain solution components can effectively tune the polymorphic phase boundaries (PPB) in KNN-based ceramics to realize multiphase coexistence, , flattening the thermodynamic energy profiles and enhancing the intrinsic contribution of spontaneous polarization, thereby strengthening the material’s piezoelectric properties. ,,,− However, the mechanical quality factor ( Q m ) and dielectric loss (tan δ) will experience large deterioration, primarily due to the facilitated domain wall motion. ,,, On the contrary, acceptor doping introduces an oxygen vacancy (V O ·· ) providing a strong pinning center that clamps the domain wall motion, accounting for the greatly decreased loss and enhanced Q m , but there is a significant sacrifice in piezoelectric coefficient …”