The temperature dependence of piezoelectric properties (direct piezoelectric coefficient d33, converse piezoelectric coefficient d33(E = 0), strain S and electromechanical coupling coefficient kp) for two niobate‐based lead‐free piezoceramics have been contrasted. 0.92(Na0.5K0.5)NbO3–0.02(Bi1/2Li1/2)TiO3–0.06BaZrO3 (6BZ/2BLT/92NKN) has a morphotropic phase boundary (MPB) between rhombohedral and tetragonal at room temperature and 0.92(Na0.5K0.5)NbO3–0.03(Bi1/2Li1/2)TiO3–0.05BaZrO3 (5BZ/3BLT/92NKN) features an MPB engineered to be located below room temperature. At 30°C, d33, d33(E = 0), S (at 2 kV/mm), and kp are 252 pC/N, 230 pm/V, 0.069%, 0.51 for 5BZ/3BLT/92NKN; and 348 pC/N, 380 pm/V, 0.106%, 0.57 for 6BZ/2BLT/92NKN, respectively. With increasing temperature, the piezoelectric properties decrease. At 200°C, d33, d33(E = 0), S (at 2 kV/mm), and kp are 170 pC/N, 160 pm/V, 0.059%, 0.36 for 5BZ/3BLT/92NKN; and 181 pC/N, 190 pm/V, 0.061%, 0.39 for 6BZ/2BLT/92NKN. It is found that the electromechanical coupling coefficient has a better temperature stability than the piezoelectric coefficient in the studied system due to a large temperature‐dependent compliance change. The results demonstrate that engineering an MPB is highly effective in tailoring temperature stability of piezoceramics.

The effect of external mechanical fields on relaxor 0.94(Na 1/2 Bi 1/2 )TiO 3 -0.06BaTiO 3 was investigated by means of temperature-and stress-dependent dielectric constant measurements between 223 and 673 K. Analogous to previous investigations that showed an electric-field-induced ferroelectric long-range order in relaxor ferroelectrics, we show that compressive stress can also result in the transition to the long-range ferroelectric order, marked by the formation of an anomaly in the permittivity-temperature curves and a nonlinear, remanent change in permittivity during mechanical loading. In situ stress-dependent high-energy x-ray diffraction experiments were performed at room temperature and reveal an apparent phase transition during mechanical loading, consistent with previous macroscopic electrical measurements. The transition lines between the relaxor states and the stress-induced ferroelectric state were determined at constant temperatures with stress-dependent dielectric constant measurements, providing a stress-temperature phase diagram.

There has been considerable progress in the development of large strain lead-free perovskite ferroelectrics over the past decade. Under certain conditions, the electromechanical properties of some compositions now match or even surpass commercially available lead-containing materials over a wide temperature range, making them potentially attractive for non-resonant displacement applications. However, the phenomena responsible for the large unipolar strains and piezoelectric responses can be markedly different to classical ferroelectrics such as Pb(Zr,Ti)O3 and BaTiO3. Despite the promising electromechanical properties, there is little understanding of the mechanical properties and fracture behavior, which is crucial for their implementation into applications where they will be exposed to large electrical, mechanical, and thermal fields. This work discusses and reviews the current understanding of the mechanical behavior of large-strain perovskite lead-free ferroelectrics for use in actuators and provides recommendations for further work in this important field.

Articles you may be interested inAging-induced two-step ferroelectric-to-paraelectric transition in acceptor-doped ferroelectrics Appl. Phys. Lett. 96, 082906 (2010); 10.1063/1.3309697 Effect of large strain on dielectric and ferroelectric properties of Ba 0.5 Sr 0.5 TiO 3 thin films Appl. Phys. Lett. 95, 012907 (2009); 10.1063/1.3151961 Effect of in-plane shear strain on phase states and dielectric properties of epitaxial ferroelectric thin filmsThe dielectric behavior near the ferroelectric-to-paraelectric phase transition of h001i C -oriented single crystal and polycrystalline barium titanate (BaTiO 3 ) was investigated as a function of uniaxial compressive stress in the temperature range from 25 to 200 C. An increase in the Curie point (T C ) and decrease in the Curie-Weiss temperature (h) were observed with increasing stress for both single crystal and polycrystalline samples, resulting in an increase in the first order nature of the phase transition as measured by the temperature difference (T C -h). With increasing applied stress levels, the permittivity versus temperature curves of polycrystalline samples were found to broaden and flatten near the Curie point, which was not observed for the single crystals. The experimental results were analyzed using a classical 2-4-6 Landau polynomial. The observed increase in the first order nature of the ferroelectric-to-paraelectric phase transition with uniaxial stress was explained by a linear dependence of the quartic coefficient of the Landau series on stress. V C 2013 American Institute of Physics. [http://dx.

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