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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 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 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]

Sintering conditions govern the optimized functional properties of ceramics. However, solid-state processing of Bi1/2K1/2TiO3 (BKT), an important end member for lead-free piezoelectric solid solutions suitable for higher temperature (≤ 300 °C) transducer applications, is challenging due to the low melting temperature (≈1070 °C). In this work, the sintering temperature (1030 °C, 1050 °C, and 1060 °C) and dwell time (10 h, 20 h, and 40 h)-dependent functional properties of solid-state processed BKT were investigated, where the sintering condition-dependent dielectric and electromechanical properties were correlated with the variations in crystal structure and microstructure. Although X-ray diffraction data revealed a single-phase tetragonal structure of BKT at room temperature for all sintering conditions, significant changes in both the tetragonal distortion and spontaneous relaxor-ferroelectric transition were observed, which were directly related to the optimized functional properties. In addition, Rayleigh behavior of the piezoelectric coefficient was characterized between −150 °C and 400 °C, demonstrating that the electromechanical response is dominated by the intrinsic contribution, which can be explained by large tetragonal distortion and associated suppression of non-180° domain wall motion. [ABSTRACT FROM AUTHOR]

The temperature-dependent Rayleigh behavior of polycrystalline lead-free Li x (Na 0.5 K 0.5) 1-x NbO 3 ceramics was characterized to measure the reversible and irreversible piezoelectric response of different compositions with varying Li content. The results revealed that all compositions showed peak values of both reversible and irreversible piezoelectric response near the polymorphic phase boundary. Additionally, depending on the crystal structure, Li content affected the irreversible and reversible contributions. Specifically, at room temperature, there was a notable increase in the irreversible contribution with rising Li content, whereas, within the tetragonal region, the change in Li content predominantly influenced the reversible contributions, resulting in their reduction. These results are discussed in conjunction with temperature-dependent X-ray diffraction and transmission electron microscopy data, which indicated that the lattice distortion and domain structure play an important role in the temperature-dependent variation in the piezoelectric response. [Display omitted] [ABSTRACT FROM AUTHOR]

The mechanical behavior of polycrystalline lead-free (1- x )BiFeO 3 - x BaTiO 3 (BF-BT) piezoelectric ceramics was investigated under uniaxial compressive stress from room temperature up to 400 °C with macroscopic stress-strain measurements and in situ stress-dependent neutron diffraction. Stress-strain curves revealed a changing mechanical response with BaTiO 3 content and temperature. With decreasing BaTiO 3 content there was an increase in the coercive stress, which reduced the remanent strain and hysteresis. Full pattern structural refinement of the neutron data reveals both rhombohedral distortion and magnetic moment decreases with increasing BaTiO 3 content. In situ stress-dependent neutron diffraction experiments showed that accommodation of external stress occurs through the changes in tilt magnitude and anisotropy of oxygen octahedra at room temperature. The origin of stress-induced strain at room temperature is a lattice deformation without any apparent change in average crystallographic symmetry or domain switching. Temperature-dependent in situ stress-induced measurement of BF-30BT showed maximum strain close to the rhombohedral - pseudocubic transition temperature, which has been proposed to be due to the lattice deformation as well as to the differing degree of tilting of the (Fe/Ti)O 6 octahedra. [ABSTRACT FROM AUTHOR]

The microscopic contributions to the electric-field-induced macroscopic strain in a morphotropic 0.93(Bi1/2Na1/2TiO3)-0.07(BaTiO3) with a mixed rhombohedral and tetragonal structure have been quantified using full pattern Rietveld refinement of in situ high-energy x-ray diffraction data. The analysis methodology allows a quantification of all strain mechanisms for each phase in a morphotropic composition and is applicable to use in a wide variety of piezoelectric compositions. It is shown that during the poling of this material 24%, 44%, and 32% of the total macroscopic strain is generated from lattice strain, domain switching, and phase transformation strains, respectively. The results also suggest that the tetragonal phase contributes the most to extrinsic domain switching strain, whereas the lattice strain primarily stems from the rhombohedral phase. The analysis also suggests that almost 32% of the total strain is lost or is a one-time effect due to the irreversible nature of the electric-field-induced phase transformation in the current composition. This information is relevant to on-going compositional development strategies to harness the electric-field-induced phase transformation strain of (Bi1/2Na1/2)TiO3-based lead-free piezoelectric materials for actuator applications. [ABSTRACT FROM AUTHOR]

Abstract: The large signal macroscopic strain response during an applied bipolar electric field is calculated from field-dependent in situ XRD data using expressions for, first, a lattice strain contribution and, second, a ferroelastic strain contribution. The lattice strain contribution is estimated using a weighted average of the lattice strains for the observed reflections along the field direction. The ferroelastic strain contribution is calculated by integrating the lattice parameter changes weighted with the ferroelastic domain distribution over all orientations relative to the direction of the applied field. Structural parameters are determined by means of both single peak fitting and Rietveld refinements. A large ferroelastic contribution is found for tetragonal (1− x)Ba(Zr0.2Ti0.8)O3 − x(Ba0.7Ca0.3)TiO3 materials that appears to be the dominant origin for the large signal macroscopic strain. The strong changes in lattice parameters and the decrease in tetragonality as a function of orientation and electric field also indicate a large influence of microstructure constraints on the macroscopic strain response. The total strain calculated from X-ray diffraction using both methods is in good agreement with macroscopic strain measurements. [Copyright &y& Elsevier]

Sintering conditions govern the optimized functional properties of ceramics. However, solid-state processing of Bi1/2K1/2TiO3 (BKT), an important end member for lead-free piezoelectric solid solutions suitable for higher temperature (≤ 300 °C) transducer applications, is challenging due to the low melting temperature (≈1070 °C). In this work, the sintering temperature (1030 °C, 1050 °C, and 1060 °C) and dwell time (10 h, 20 h, and 40 h)-dependent functional properties of solid-state processed BKT were investigated, where the sintering condition-dependent dielectric and electromechanical properties were correlated with the variations in crystal structure and microstructure. Although X-ray diffraction data revealed a single-phase tetragonal structure of BKT at room temperature for all sintering conditions, significant changes in both the tetragonal distortion and spontaneous relaxor-ferroelectric transition were observed, which were directly related to the optimized functional properties. In addition, Rayleigh behavior of the piezoelectric coefficient was characterized between −150 °C and 400 °C, demonstrating that the electromechanical response is dominated by the intrinsic contribution, which can be explained by large tetragonal distortion and associated suppression of non-180° domain wall motion. [ABSTRACT FROM AUTHOR]