The polarization and strain behavior of Ba(Ti1−xZrx)O3 (x=0–0.3) ceramics are studied. The unipolar strain levels of ∼0.18% at 40 kV/cm and of ∼0.25% at ∼120 kV/cm with small hysteresis were obtained for the ceramics with 0.03⩽x⩽0.08. The remnant polarization is ∼13–18 μC/cm2 for 0.03⩽x⩽0.08 and below 2 μC/cm2 for 0.15⩽x⩽0.3 at room temperature. The electromechanical coupling coefficient K33=56.5% and the piezoelectric stain coefficient d33=236 pC/N were obtained for the ceramics with x=0.05. These results indicated that the Ba(Ti1−xZrx)O3 system is a promising lead-free high strain material for applications.
The effect of dc electric field (E) on the dielectric properties of Ba(Ti0.7Zr0.3)O3 ceramics with an obvious ferroelectric-relaxor behavior (Tm∼229 K, 10 kHz) is reported. The dielectric constant is greatly suppressed and a low loss is obtained under dc electric fields (⩽40 kV/cm). The low loss (tan δ∼0.002) and high tunability (∼45%) were obtained for the Ba(Ti0.7Zr0.3)O3 ceramics around 300 K, indicating that it is a promising candidate for tunable materials at room temperature. The field dependence of the temperature (Tm) of the dielectric constant maximum follows the ΔTm∼E2/3 relation, indicating a second-order phase-transition-like behavior.
The dielectric properties, ferroelectric polarization, and piezoelectric strain behavior of Ba(Ti1−xZrx)O3 (x=0.05 and 0.08) single crystals are studied for different crystal orientations. The study of dielectric properties suggests that the three phase transitions in BaTiO3 are pinched by substituting Ti with Zr but the anisotropic dielectric behavior is present in crystals of various orientations. The remnant polarization and strain behavior are also studied for different crystal directions. Higher strain and lower polarization are obtained along the pseudocubic 〈001〉 direction compared to those observed along the 〈110〉 and 〈111〉 directions in both orthorhombic (x=0.05) and rhombohedral (x=0.08) phase. The results for the 〈001〉 oriented orthorhombic crystals with x=0.05 indicate the highest strain level (∼0.25%) with almost hysteresis-free behavior and high piezoelectric coefficient (d33=500 pC/N).
Grain-oriented glass-ceramics of LizSizOs, fresnoite (BazTiSizOs), and its isomorphs Sr2TiSi208 and BazTiGe2Os, were prepared by recrystallizing glasses in a temperature gradient. Electromechanical and hydrostatic piezoelectric properties of these glass-ceramics were measured. Piezoelectric voltage coefficients g , and hydrostatic voltage coefficient gh of these glass-ceramics are comparable to those of polyvinylidene fluoride and an order of magnitude higher than the corresponding values of lead zirconate-titanate. These glass-ceramics seem to be attractive candidate materials for hydrophones and several piezoelectric devices. Hydrostatic piezoelectric properties of BazTiSizOs and BazTiGeZO8 single crystals were also measured. The unusually high values of gh in fresnoite single crystals and glass-ceramics are supposed to be due to positive d3, in these materials. A composite model is proposed to explain the positive sign of d3, in fresnoite based on its crystal structure and internal Poisson's ratio stress.
Ferroelectric (Pb,Sr)TiO3 (PSTO) thin films were epitaxially grown on (001) LaAlO3 (LAO) by using pulsed laser deposition. Microstructural characterizations with x-ray diffraction and transmission electron microscopy indicate that the as-grown films have excellent single crystalline quality and a (001)PSTO∕∕(001)LAO and [100] PSTO∕∕ [100] LAO interface relationship. Dielectric property measurements reveal that the as-grow films have a very high dielectric constant value of 3100 and very large dielectric tunability of 48% at 40V∕cm at room temperature. These excellent results suggest that the highly epitaxial ferroelectric (Pb,Sr)TiO3 thin films can be developed for room-temperature tunable microwave elements in wireless communication applications.
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