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Adding excessive metal oxide doping to a powder batch is a known way to compensate for the loss of volatile cation species during high temperature sintering. An important case in the piezoelectric ceramics is the bismuth oxide in the lead-free ferroelectric ceramic bismuth sodium titanate (BNT). Building from the earlier knowledge about excessive bismuth oxide's influences on the properties of BNT, we further note that varying the sintering temperature can both control the distribution of excessive Bi3+ and impact the relaxor/normal ferroelectric behaviors and corresponding phase transition. In addition to the nature of polarization, the sintering temperature also significantly manipulates the electrical conductivity. A hypothetical mechanism for the resistive grain boundary is proposed, based on inferences from electrical—microstructure—processing relations in 85% Bi0.5Na0.5TiO3-15% BaTiO3 with batched Bi2O3 excess and acceptor Mg2+ in a co-doped strategy. [ABSTRACT FROM AUTHOR]

The sintering of functionalized particles is an approach often used to obtain high performance functional ceramics. When molecular surfactants are used to functionalize particles, conventional sintering cannot be applied due to extremely high processing temperatures. Here, BaTiO3 particles are grafted with different coverages using a catechol (CA) surfactant, and then these particles are densified under cold sintering with a (BaOH2)⋅8H2O transient flux. The adsorption of CA is equilibrated with various concentrations on BaTiO3 particles at room temperature. The modeling (Langmuir and Freundlich adsorption) and the quantification (UV–vis absorption and thermogravimetric analysis) of CA coverage enable us to rigorously determine the degree of functionalization and conduct thorough cold sintering kinetics investigations as a function of CA coverage using a dilatometer. Microstructure is observed with electron microscopy techniques to determine the grain and grain boundary interfaces that result with the competition of surfactant coverage and densification driven by the dissolution and reprecipitation processes at the interfaces. A mechanism with the retardation of cold sintering kinetics is discussed based on these experimental observations. [ABSTRACT FROM AUTHOR]

The dielectric property relations of a series of BaTiO3–polymer composites with a uniquely high-volume fraction of ceramic [(1 − x)BaTiO3–x polytetrafluoroethylene (PTFE), with volume fractions x = 0.025, 0.05, 0.1, and 0.2] are studied. Such high-volume fraction of the BaTiO3 phase is achieved by using the cold sintering process, as it enables a single-step densification of oxides at an extremely low temperature; typically, the volume fractions from other processing methods are limited to ceramic filler volume fractions of ∼0.6. Microstructural and resistivity analyses suggest that the optimal range of the polymer content to effectively enhance the functions is x = 0.05, as higher volume fractions of the polymer hinder the densification of the ceramic. The composite exhibits improved properties such as lower loss tangent, higher resistivity, and high permittivity that vary systematically with x following an empirical mixing law. Here, we consider the composite mixing law trends and the changes to properties, which indicate that size effects are also being induced in the dielectric response, including shift of Tc, broadening of transition, and reduction of permittivity with respect to volume fraction of the PTFE. Our findings provide a new and simple strategy for the fabrication of ceramic–polymer composites with extremely high relative permittivities and resistivities, and these observations all point to a route that can allow us to engineer new types of advanced dielectric materials. [ABSTRACT FROM AUTHOR]

Hierarchical domain structures associated with oxygen octahedra tilting patterns were observed in lead-free (Bi1/2Na1/2)TiO3 ceramics using aberration-corrected high-resolution transmission electron microscopy (HRTEM). Three types of domains are induced by distinct mechanisms: the 'orientation-domain' is induced at micrometer scale formed by different tilting orientations of the oxygen octahedra, the 'meso-chemical-domain' occurs at a few tens of nanometer scale by chemical composition variation on the A-site in the ABO3 perovskite structure, and the 'nano-cluster-region' runs across several unit-cells with apparent A-site cation segregation with oxygen vacancies clustering around Na cations. Based on HRTEM amplitude contrast imaging (ACI), the correlation between the oxygen octahedral tilting pattern and compositional non-stoichiometry was established. The role of the hierarchical domain structure associated with the tilting patterns of the oxygen octahedra on the ferroelectric behavior of (Bi1/2Na1/2)TiO3 is also discussed. [ABSTRACT FROM AUTHOR]

Hierarchical domain structures associated with oxygen octahedra tilting patterns were observed in lead-free (Bi1/2Na1/2)TiO3 ceramics using aberration-corrected high-resolution transmission electron microscopy (HRTEM). Three types of domains are induced by distinct mechanisms: the 'orientation-domain' is induced at micrometer scale formed by different tilting orientations of the oxygen octahedra, the 'meso-chemical-domain' occurs at a few tens of nanometer scale by chemical composition variation on the A-site in the ABO3 perovskite structure, and the 'nano-cluster-region' runs across several unit-cells with apparent A-site cation segregation with oxygen vacancies clustering around Na cations. Based on HRTEM amplitude contrast imaging (ACI), the correlation between the oxygen octahedral tilting pattern and compositional non-stoichiometry was established. The role of the hierarchical domain structure associated with the tilting patterns of the oxygen octahedra on the ferroelectric behavior of (Bi1/2Na1/2)TiO3 is also discussed. [ABSTRACT FROM AUTHOR]

The polarization wake‐up process is demonstrated here for ferroelectric switching in epitaxial Al0.93B0.07N films on W coated c‐axis oriented Al2O3 (sapphire) substrates. During the wake‐up process, the remanent polarization grows from ≈0 to >100 µC cm−2. As it does so, both the reversible and irreversible Rayleigh coefficients rise substantially, suggesting that the concentration of mobile interfaces that separate regions of opposite dipole orientation is increasing. The irreversible Rayleigh coefficient is very small (≈3.5 × 10−4 cm kV−1), four to five orders of magnitude below those of perovskite ferroelectric films such as PbZr0.52Ti0.48O3. These small values are consistent with the high coercive fields observed in the nitride ferroelectrics. The temperature dependence of the Rayleigh coefficients suggests that the interface motion is thermally activated. On increasing frequency, the Rayleigh coefficients drop, suggesting time‐dependent pinning processes also occur in this family of materials. With information from anisotropic etching experiments upon field‐cycling, a self‐consistent model that describes a polar domain microstructure evolution process during wake‐up is proposed. [ABSTRACT FROM AUTHOR]

Advancing the atomistic level understanding of aqueous dissolution of multicomponent materials is essential. We combined ReaxFF and experiments to investigate the dissolution at the Li1+xAlxTi2−x(PO4)3-water interface. We demonstrate that surface dissolution is a sequentially dynamic process. The phosphate dissolution destabilizes the NASICON structure, which triggers a titanium-rich secondary phase formation. [ABSTRACT FROM AUTHOR]

(Bi1/2Na1/2)TiO3 (BNT) is a lead-free ferroelectric material, which has shown promising electromechanical properties and energy storage capacities. These attractive functionalities and property performances are attributed to the relaxor behavior of BNT. However, the nature of the dielectric relaxation is not well understood in these materials, and the physical meaning of some important parameters associated with the permittivity is still under debate. In this Letter, we focus on the dielectric "shoulder," Ts, that is readily seen in the ε′–T curve of every BNT-based relaxor. It is found that the Ts is controlled by not only the typical compositional engineering but also by the thermal, electrical, or mechanical history. From a moderate temperature (≤250 °C), a sample can be rapidly cooled to room temperature or slowly cooled under an electrical bias or a mechanical bias in the form of a compressive stress. All three treatments lead to a nearly identical effect, which is to alter the Ts with respect to rest of the ε′–T curve that remains unperturbed. Therefore, the internal stress is identified to be a general perturbance to the polarization dynamics. Finally, the "breathing" model is revisited to interpret the physical meaning of Ts for these BNT materials under these metastable conditions. [ABSTRACT FROM AUTHOR]

(Bi1/2Na1/2)TiO3 (BNT) is a lead-free ferroelectric material, which has shown promising electromechanical properties and energy storage capacities. These attractive functionalities and property performances are attributed to the relaxor behavior of BNT. However, the nature of the dielectric relaxation is not well understood in these materials, and the physical meaning of some important parameters associated with the permittivity is still under debate. In this Letter, we focus on the dielectric "shoulder," Ts, that is readily seen in the ε′–T curve of every BNT-based relaxor. It is found that the Ts is controlled by not only the typical compositional engineering but also by the thermal, electrical, or mechanical history. From a moderate temperature (≤250 °C), a sample can be rapidly cooled to room temperature or slowly cooled under an electrical bias or a mechanical bias in the form of a compressive stress. All three treatments lead to a nearly identical effect, which is to alter the Ts with respect to rest of the ε′–T curve that remains unperturbed. Therefore, the internal stress is identified to be a general perturbance to the polarization dynamics. Finally, the "breathing" model is revisited to interpret the physical meaning of Ts for these BNT materials under these metastable conditions. [ABSTRACT FROM AUTHOR]

In the design of the ceramic capacitor, high capacitance, temperature stability, and high operating voltage must be balanced against the failure mechanisms of degradation. Cold sintering is used to develop dense BaTiO3 – poly (p‐phenylene oxide) (PPO) nanocomposites with PPO throughout the grain boundary microstructure. To obtain the desired PPO distribution, a process is introduced that distributes the polymers on the BaTiO3 powders prior to the cold sintering process. With the cold sintering enabled by a Ba(OH)2·8H2O transient phase, theoretical densities ≈95% could be obtained at a sintering temperature ≈225 °C with up to 15 vol% PPO content. The rationale is to influence the local electric field distribution within the dielectric, to maximize resistivity (1013–1014 Ω cm) and degradation resistance, minimize temperature dependence of permittivity, and minimize the field dependent permittivity. All these properties are investigated as a function of the volume fraction of PPO. The magnitude of the permittivity follows a logarithmic mixing law: 1460 to 680 for the nanocomposite with 5 to 15 vol% PPO content, respectively, at room temperature. The BaTiO3‐PPO composite dielectrics are contrasted under accelerated lifetime testing conditions, noting superior resistance toward degradation kinetics, indicating an important breakthrough opportunity towards the development of high reliability dielectrics. [ABSTRACT FROM AUTHOR]