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The correlation between the ferroelectric fatigue and variations in piezoelectric properties in a 8/65/35 (Pb, La) (Zr, Ti)O3 thick film was studied by simultaneous measurements of the polarization hysteresis loop, the strain-field loop, the piezoelectric constant, and the dielectric constant during cycling. It was found that the fatigue reflects itself in the variations of the piezoelectric constant and the induced strain. Namely, during cycling both quantities decrease for the same relative amount as the remanent polarization. In addition, the effective electrostriction constant as a function of switching cycles was determined.

We report on the frequency and stress dependence of the direct piezoelectric d33 coefficient in BiFeO3 ceramics. The measurements reveal considerable piezoelectric nonlinearity, i.e., dependence of d33 on the amplitude of the dynamic stress. The nonlinear response suggests a large irreversible contribution of non-180{\deg} domain walls to the piezoelectric response of the ferrite, which, at present measurement conditions, reached a maximum of 38% of the total measured d33. In agreement with this interpretation, both types of non-180{\deg} domain walls, characteristic for the rhombohedral BiFeO3, i.e., 71{\deg} and 109{\deg}, were identified in the poled ceramics using transmission electron microscopy (TEM). In support to the link between nonlinearity and non-180{\deg} domain wall contribution, we found a correlation between nonlinearity and processes leading to deppining of domain walls from defects, such as quenching from above the Curie temperature and high-temperature sintering. In addition, the nonlinear piezoelectric response of BiFeO3 showed a frequency dependence that is qualitatively different from that measured in other nonlinear ferroelectric ceramics, such as "soft" (donor-doped) Pb(Zr,Ti)O3 (PZT); possible origins of this dispersion are discussed. Finally, we show that, once released from pinning centers, the domain walls can contribute extensively to the electromechanical response of BiFeO3; in fact, the extrinsic domain-wall contribution is relatively as large as in Pb-based ferroelectric ceramics with morphotropic phase boundary (MPB) composition, such as PZT. This finding might be important in the search of new lead-free MPB compositions based on BiFeO3 as it suggests that such compositions might also exhibit large extrinsic domain-wall contribution to the piezoelectric response., Comment: 38 pages, 11 figures

High-density KTaO3 ceramics were synthesized and studied by means of microwave, terahertz, infrared, and Raman spectroscopies. The results were analyzed together with recently published radio-frequency data. [S. Glinsek et al., J. Am. Ceram. Soc. 94, 1368 (2011)] Three polar modes expected for the cubic structure were observed. As in single crystals, the lowest-frequency TO1 mode (soft mode) strongly softens on cooling, while the TO2 and TO4 mode frequencies do not change with temperature. The permittivity does not show any significant dispersion below the soft mode frequency and its value in the kHz and GHz range is mainly given by the intrinsic polar lattice modes contribution. The soft mode frequency agrees with the values found in single crystals; this indicates a negligible influence of the grain boundaries on the dielectric response in KTaO3 unlike in other ferroelectric or incipient ferroelectric perovskite ceramics.

The electrocaloric effect (ECE), i.e., the conversion of electric energy into heat, is of great importance for application in new generation cooling or heating devices that would be friendlier to the environment. Here, utilizing direct measurements of the ECE change of the temperature ΔT via a high resolution calorimeter, we study the ECE as a function of the magnitude of the electric-field step E in the vicinity of the critical point in several bulk relaxor ferroelectric ceramic systems. Relatively large ΔT of ∼2 to 3 K were obtained at modest fields of 90 kV/cm, even in the case of ceramic materials. The effective responsivity ΔT/E as a function of the electric field shows a characteristic peak near the critical point, which demonstrates the importance of proximity to the critical point for the enhancement of the electrocaloric effect. Experimental results are in good agreement with the theoretical calculations based on the spherical random-bond random-field model.

Direct measurements of the motion of domain walls in disordered ferroelectrics provide important information on their interaction with defects, which is crucial for the functioning of various ferroelectric devices such as high-K capacitors and ferroelectric-based memories. In this work, we report on the results of the nanoscale measurements of domain-wall velocity and static domain-wall roughness in disordered (Pb,La)(Zr,Ti)O3 (PLZT) ceramics prepared by hot press sintering. Relaxation of domain walls to their equilibrium configurations at short length scales yields the apparent roughness exponent ζ ≈ 0.67 in PLZT 9.5/65/35. At the same time, the dynamical exponent μ was found to be about 0.25 from the independent measurements of domain-wall creep under local application of electric field. An analysis of these two values points to the effective dimensionality deff = 1 for the domain walls in PLZT with high La content. This result is confirmed by the layer-by-layer polishing followed by the imaging of an a...

The influence of thermal stresses versus the phase composition for 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 (0.65PMN–0.35PT) thick films is being reported. The thermal residual stresses in the films have been calculated using the finite-element method. It has been observed that in 0.65PMN–0.35PT films a compressive stress enhances the thermodynamic stability of the tetragonal phase with the space group P4mm.

Phase transitions of sodium niobate, prepared by the solid state synthesis method, were examined using dielectric measurements, differential scanning calorimetry, and high temperature x-ray diffraction, in order to contribute to the clarification of its structural behavior below 400 °C. Four phase transitions were detected in the ceramic sample using dielectric measurements and differential scanning calorimetry and the obtained temperatures were in a good agreement with previous reports for the transitions of the P polymorph. The anomaly observed by dielectric measurements in the vicinity of 150 °C was frequency dependent and could be related to the dynamics of the ferroelectric nanoregions. The phase transitions of the as-synthesized NaNbO3 powder were investigated using differential scanning calorimetry and high temperature x-ray diffraction. The results show the existence of the Q polymorph at room temperature, not previously reported for the powder, which undergoes a transition to the R polymorph upon...

The dielectric, ferroelectric, piezoelectric, and electrostrictive properties of K0.5Na0.5NbO3 single crystals (KNN s.c.) prepared by solid-state crystal growth are reported. The dielectric constant (e), dielectric losses (tan δ), remanent polarization (Pr), and coercive field (Ec) for KNN s.c. in the [13¯1] direction at room temperature are 1015, 1%, 17 μC/cm2, and 24 kV/cm, respectively. The influence of 180° domains to the linear piezoelectric response and quadratic electrostrictive response of KNN s.c. is discussed. The piezoelectric coefficient d33 and the electrostrictive coefficient M33 of KNN s.c. measured using atomic force microscopy at 2 Hz was 80 pm/V and 2.59×10−14 m2/V2, respectively. The extremely high M33 value can be explained by the extrinsic strain from the domain-wall motion. The properties of the surrounding polycrystalline KNN ceramic are added for comparison.

The electromechanical behavior of 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 (0.65PMN-0.35PT) thick films, screen printed and fired on alumina substrates, was investigated using an atomic force microscope. A quadratic relation between the induced strain and the electric field was found and is discussed here. The electrostrictive coefficient M33 was determined to be 7.6×10−16 m2/V2. The determined tetragonal crystal structure, the frequency independence of the dielectric maxima as a function of temperature, and the hysteresis loop with a remanent polarization of 31 μC/cm2 and a coercive field of 40 kV/cm confirm the ferroelectric nature of the developed 0.65PMN-0.35PT thick films.

We have detected a typical relaxor/glasslike dielectric response in the derived lead-free (1−x)K0.5Na0.5NbO3-(x)SrZrO3 ceramic system. In the compositional range 0.10≤x≤0.33, where solid solubility was observed, the system exhibits a broad dispersive dielectric maximum, a Vogel–Fulcher temperature dependence of the characteristic relaxation frequency, and a paraelectric-to-glass crossover in the temperature dependence of the dielectric nonlinearity. As the relatively high values of the dielectric constant, exceeding 5000 in the x=0.15 compound, are only weakly dependent on the frequency in the range of 20 Hz–1 MHz, and, furthermore, the history-dependent effects play only a minor role in comparison to some widely used lead-based relaxors, this environmentally friendly system seems to be very promising for a variety of applications.

The elastic strain of lead-free relaxor K0.5Na0.5NbO3–SrTiO3 ceramic system, induced by applied electric fields with amplitudes up to 40kV∕cm, has been investigated. The strain response, being similarly low (order of 10−5) as in the classical lead magnesium niobate relaxor, is shown to be of solely electrostrictive origin, as a pure quadratic relation holds between induced strain and electric polarization. The strain dependence on the SrTiO3 content is presented and discussed. Furthermore, electrostrictive coefficients are shown to be constant over a broad temperature range and, similar to dielectric properties, independent of electric-field cycles, which suggests possible applications of this translucent, high-dielectric constant, and environmental-friendly ceramic system.