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The functional properties of piezoelectric ceramic materials, such as barium titanate, are highly dependent on grain size. Lead-free polycrystalline Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) samples were prepared with a combination of the hydrothermal method and spark plasma sintering to achieve grain sizes from 100 nm to 10 μm by varying the maximum sintering temperature. In this range, a transition from a nearly linear dielectric to a ferroelectric response can be seen in macroscopic electromechanical measurements, demonstrating the importance of grain size on functional properties in BCZT. Furthermore, in situ electric field-dependent synchrotron x-ray diffraction measurements were performed to quantify the intrinsic and extrinsic strain contributions and their variations with grain size. At lower grain sizes, the data revealed a significant loss of extrinsic contributions in the piezoelectric behavior, limiting the response to intrinsic contribution associated with lattice strain. For BCZT, a critical grain size between approximately 0.08 and 0.18 μm is proposed, below which no piezoelectric response was observed. [ABSTRACT FROM AUTHOR]

Despite the extraordinary significance of high-temperature piezoelectric ceramics in engineered systems, understanding their macroscopic electromechanical response in terms of local underlying phenomena, in particular the domain dynamics at elevated temperatures that directly influence the stability of device performance, remains a significant challenge. Here, we investigate the relationship between domain evolution with temperature and its piezoelectric response utilizing 0.7Bi1.05FeO3-0.3BaTiO3 (BF30BT), a critical alternative to lead-based ferroelectrics for high-temperature applications. By analyzing the frequency and loading amplitude-dependent Rayleigh behavior, we are able to demonstrate the importance of the intrinsic contributions in piezoelectric response. The re-entrant relaxor nature of BF30BT results in active locally heterogeneous nanodomains that display reversible rapid response contributions rather than typical extrinsic contributions due to their low activation energy. Decoding the complicated domain dynamics of BF30BT allows for the further integration of microstructures and macroscopic characteristics, guiding the design and utilization of further high-temperature piezoelectric ceramics. [ABSTRACT FROM AUTHOR]

BiFeO3 is a ferroelectric with a Curie temperature of 830 °C, however, its piezoelectric performance at high temperature remains unclear. The current work reveals a disappearance/recovery of piezoelectricity in BiFeO3 at elevated temperature and upon cooling. In particular, that temperature is strongly frequency‐dependent and ranges from 280 to 430 °C between 0.5 and 140 Hz, respectively. Meanwhile, in situ and ex situ X‐ray diffraction and piezoresponse microscope analysis demonstrate thermally‐resistant domain texture to temperatures as high as 750 °C. This demonstrates that the piezoelectricity of BiFeO3 is strongly influenced by its resistance/conductance variations due to charge carrier motion limiting the operational frequency. The investigation enhances the understanding of BiFeO3 complex piezoelectric behavior at various temperatures, offering insights into its potential applications. [ABSTRACT FROM AUTHOR]

This study investigates the development of freestanding thick films (FSFs) of lead-free (Ba,Ca)(Zr,Ti)O3 and the role of grain growth on the electromechanical response. During deposition, room temperature powder aerosol deposition rapidly produces thick films with a nano-grain structure that limits the electromechanical properties. In this study, the films are removed from the substrate using a sacrificial buffering layer to avoid thermal treatment and allow for an initial as-processed state. Following this, FSFs were thermally treated at various annealing temperatures from 800 °C to 1400 °C to induce grain growth, which was characterized with scanning and transmission electron microscopy. X-ray diffraction revealed an increase in the crystallite size consistent with an increase in grain size and a decrease in internal residual stress. The temperature-dependent dielectric behavior and the large-field ferroelectric response were also characterized, revealing significant differences of the FSFs from the bulk properties. [ABSTRACT FROM AUTHOR]

Recent research has found that by introducing A‐site deficiency into Ba/Ni co‐doped (K,Na)NbO3 ABO3‐type perovskite, a beneficial interface for photoferroelectric applications is formed between the perovskite and tungsten bronze (TB) phases. To date, such an interface is formed only spontaneously, and the growth mechanism of the TB phase in the perovskite phase is unclear. This work investigates controlled interface formation using KNBNNO (K0.50Na0.44Ba0.04Ni0.02Nb0.98O2.98) annealed at different temperatures for different durations, and in various atmospheres. Structural, microstructural, and chemical analyses suggest that vacuum, N2, and O2 atmospheres promote the growth of the TB phase from the sample surface, of which the thickness increases with annealing temperature and duration. In contrast, annealing in air does not promote such growth due to lower evaporation of K and Na. Among all atmospheres, the growth starts the earliest, i.e., at 800 °C, in vacuum compared to that as late as 1000 °C in O2. The association of growth of the TB phase with the degree of alkali volatilization that is dependent on the atmosphere, and that with the resultant variation in diffusion rate, uncovers the formation mechanism of the beneficial interface that may also be applicable to other KNN‐based materials for advanced photoferroelectric applications. [ABSTRACT FROM AUTHOR]

Na1/2Bi1/2TiO3 (NBT) with varying Bi content has gained significant interest as a potential new material for solid-oxide fuel cells and oxygen separation membranes because of its excellent oxygen-ion conductivity. In this work, the effect of varying Bi content in NBT ceramics of compositions Na1/2BixTiO2.25+1.5x, where x = 0.485–0.510, on the temperature-dependent mechanical and dielectric properties and the crystal structure has been investigated, as these applications expose the components to high thermal and mechanical fields. The effects of Bi variation on phase compositions and structural transitions were systematically investigated by scanning electron microscopy-energy dispersive x-ray analyses and neutron diffraction at room temperature, in situ high-temperature x-ray diffraction, dielectric permittivity, and mechanical measurements. In-depth analysis of the temperature-dependent data shows that the Bi content of the samples does not alter the average crystal structure of the NBT; however, the temperature-dependent behavior of the latter depend on variations in Bi content and the associated oxygen vacancy concentration. This change in phase transition temperature displays a good correlation with the temperature-dependent ferroelastic response and with the Bi content. [ABSTRACT FROM AUTHOR]

Lead-free (Li,Na,K)NbO3-based multilayered piezoceramics were prepared, and their large-signal piezoelectric properties, under combined electrical and mechanical loadings, were characterized from 25 °C to 100 °C. Under zero stress, the multilayer exhibited a high large-signal piezoelectric constant d 33 ∗ (= S max / E max ) ≈ 350 pm/V with an applied unipolar field of 6 kV/mm. The stress-dependent d 33 ∗ , with a unipolar field of 6 kV/mm, featured a pronounced sensitivity to the electric field with an evolving peak at −80 MPa, which was not observed at 100 °C. The disappearance of the evolving peak with increasing temperature suggests a strong influence of the crystallographic phase on the electromechanical properties of (Li,Na,K)NbO3-based multilayers. Further investigations of the stress–strain loop and stress–polarization change revealed that the field-dependent peak below 100 °C was due to the non-180° domain orientation induced by the combined electric field and compressive stress. [ABSTRACT FROM AUTHOR]

The ferroelectric, ferroelastic, and dielectric properties as well as the crystal structure were investigated for polycrystalline donor doped lead zirconate titanate (PZT) with grain sizes ranging from 0.25 to 5 μm, which were prepared using a novel zirconium titanium hydrate precursor (ZTH) with a specific surface area of 310 m2/g. Piezoforce microscopy was used to investigate the change in the domain structure, revealing a change in the domain configuration from a complex 3D structure to a simple lamellar domain formation at a 1 μm grain size that corresponded to a rapidly increasing internal mechanical stress observed with in situ synchrotron x-ray experiments. The correlation between the change in domain configuration, increasing internal stresses, effects of poling on the crystal structure, and the macroscopic ferroelectric and ferroelastic properties are discussed in detail, allowing a deeper understanding of size effects in polycrystalline donor doped PZT ceramics. [ABSTRACT FROM AUTHOR]

The influence of uniaxial compressive stress on small-signal relative permittivity and direct piezoelectric coefficient of polycrystalline Li-modified (K0.5Na0.5)NbO3 (0, 2, and 4 mol. % Li) was characterized as a function of temperature from 25 to 450 °C. These data reveal corresponding anomalies in both the dielectric and piezoelectric properties near the well-known structural phase transitions in (KxNa1 − x)NbO3. In particular, increasing stress was found to shift the orthorhombic–tetragonal (T O − T ) and tetragonal–cubic (T C) phase boundaries to higher temperatures, thereby stabilizing the lower symmetry phases. Experimental results also show that stress up to a critical value flattens the piezoelectric response below T O − T , above which a monotonic decrease is observed. In contrast, permittivity is increased below T O − T with increasing stress. These results are used to construct a stress–temperature phase diagram of Li-modified (K0.5Na0.5)NbO3. [ABSTRACT FROM AUTHOR]

The temperature-dependent energy storage properties of four tungsten bronze-type ceramics are studied together with an investigation of their structure and temperature-dependent permittivity response, i.e., Ba6Ti2Nb8O30 (BTN), Ba6Zr2Nb8O30 (BZN), Sr3TiNb4O15 (STN) and Sr3ZrNb4O15 (SZN) ceramics. With different cations at A and B sites, those four ceramics exhibit different crystal structures and show significantly different microstructure features and dielectric responses with changing temperatures. It was observed under SEM that BZN has smaller grains and a more porous structure than BTN. SZN shows the most porous structure among all samples, exhibiting a much lower permittivity response than other samples with no signs of phase transitions from room temperature to 400 °C. Though the energy storage response of those samples is generally quite low, they exhibit good temperature stability together with low dielectric loss. It was suggested that by obtaining a denser structure through chemical modification or other methods, those tungsten bronze ceramics with good temperature stability could be promising as energy storage devices when improved energy storage properties are achieved. [ABSTRACT FROM AUTHOR]

Tailoring the electromechanical properties of a material without altering the original composition is an emerging phenomenon for the optimization of functional properties. Post-sintering annealing with varying maximum temperatures, cooling rates, and atmospheres can influence the crystallographic phases, domain structures, conductivity, mechanical properties, and the temperature stability of the electromechanical properties. K1/2Bi1/2TiO3 (KBT) is a high-temperature stable >280 °C A-site complex perovskite piezoelectric and is critical for high-temperature applications. However, the influence of annealing conditions on crystal structure, domain structure, and functional properties is not well-known. This work demonstrates the effect of annealing cooling rate and maximum temperature on the macroscopic electromechanical response as well as the crystal and domain structure. It is shown that the room-temperature state of KBT can be reversibly switched between the ferroelectric and relaxor state, where the slow cooling from 900 °C favors the stabilization of the relaxor state and quenching induces the ferroelectric state. Importantly, the quenched sample showed a stable piezoelectric coefficient up to 368 °C in the depolarization temperature, an increase of 78 °C. The origin of ferroelectric-relaxor state change is proposed to be related to the A-site cation redistribution and the associated change in the crystal structure and domain structure. [ABSTRACT FROM AUTHOR]

The influence of stress on the small‐signal dielectric permittivity and piezoelectric coefficient of polycrystalline lead‐free perovskite 0.92(Na1/2K1/2)NbO3–(0.08 − x)Bi1/2Li1/2TiO3–xBaZrO3 (x = 0, 0.02, 0.04, 0.06, and 0.07) was characterized under different constant uniaxial stress up to −200 MPa within a temperature range of −150 to 450°C, revealing stress‐induced suppression of the electromechanical response as well as shifts in the phase boundaries. For all compositions, the interferroelectric and ferroelectric–paraelectric phase transitions were shifted to higher temperatures under the uniaxial compressive stress. Interestingly, the sensitivity to the applied stress was found to increase with increasing BZ/BLT ratio in the system. The origin of a different extent of stress‐sensitivity with BZ/BLT ratio is suggested to be related to the change in the crystal structure. Additionally, at temperatures below −50°C, the relative permittivity showed a significant increase under applied compressive stress. [ABSTRACT FROM AUTHOR]

Antiferroelectric AgNbO3 ceramic is investigated with a focus on the effects of uniaxial compressive stress on dielectric response and phase transitions as well as its frequency-dependent ferroelastic behavior. The application of uniaxial compressive stress leads to diffused phase transitions, higher phase transition temperatures, and increased permittivity parallel to the stress application direction for low-temperature phase regions (MI, MIIa). The stress-dependent permittivity response at different phase regions reveals the influence of stress on domain wall motion and phase changes. Additionally, loading rate-dependent stress–strain measurements demonstrate easier ferroelastic domain switching under a lower loading frequency, where the coercive stress increases with frequency initially while getting saturated above 5 mHz. This study reveals the impact of external stress, which can alter the dielectric response and affect domain wall movement at different extents depending on the loading frequency and shift phase boundaries of AgNbO3, implying positive prospects of property engineering of energy storage materials by stress application. [ABSTRACT FROM AUTHOR]

Antiferroelectric AgNbO3 ceramic is investigated with a focus on the effects of uniaxial compressive stress on dielectric response and phase transitions as well as its frequency-dependent ferroelastic behavior. The application of uniaxial compressive stress leads to diffused phase transitions, higher phase transition temperatures, and increased permittivity parallel to the stress application direction for low-temperature phase regions (MI, MIIa). The stress-dependent permittivity response at different phase regions reveals the influence of stress on domain wall motion and phase changes. Additionally, loading rate-dependent stress–strain measurements demonstrate easier ferroelastic domain switching under a lower loading frequency, where the coercive stress increases with frequency initially while getting saturated above 5 mHz. This study reveals the impact of external stress, which can alter the dielectric response and affect domain wall movement at different extents depending on the loading frequency and shift phase boundaries of AgNbO3, implying positive prospects of property engineering of energy storage materials by stress application. [ABSTRACT FROM AUTHOR]