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The overpoling effect of alternating current poling (ACP) was studied on [001]-orientated rhombohedral Pb(Mg1/3Nb2/3)O3-0.26PbTiO3 (PMN-0.26PT) single crystals. Our experimental results showed that the property enhancement from the ACP was remarkable only when the poling cycle number (NL) was kept low. When ACP was continued after the saturation, dielectric and piezoelectric properties gradually dropped down to traditional direct current poled levels or even lower. Such a decrease in material properties caused by the large NL during ACP was defined as the "overpoling effect of ACP" in this study. The following lattice symmetry and domain structure characterization studies were performed through x-ray diffraction (XRD) and piezoelectric force microscopy (PFM) to find the origin of the overpoling effect. The XRD measurements combined with temperature dependence of dielectric properties demonstrated that the field-induced phase transition continued when the samples became overpoled. Further PFM measurements illustrated that the domain density of the overpoled ACP sample was significantly lower than that of the normal one, while the "2R" domain configuration was maintained through the ACP process. In addition, the hysteresis loop characterization indicated large decreases in the coercive fields. The discovered overpoling effect of ACP could help us understand the mechanisms of ACP and optimize the ACP process. [ABSTRACT FROM AUTHOR]

Alternating current (electric field) poling (ACP) was applied on [001]-oriented 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-0.3PT) single crystal samples with dimensions of 5 × 1.25 × 1.25 mm3 (with electrodes on the 1.25 × 1.25 mm2 surfaces), and the influence of ACP frequency (fACP) was studied. Compared to those from traditional direct (electric field) poling samples, the piezoelectric coefficient (d33) and free dielectric constant (εT33/ε0) of ACP samples could gain up to a 67% increase to 3200 pC/N and 10 500, respectively. The influence of fACP was studied on two main aspects: saturated properties and dynamic saturation process. In general, ACP samples with lower fACP had higher saturated d33, εT33/ε0, and coupling factor k33, as well as lower dielectric loss and faster saturation speed. The ACP dynamics during the saturation process were studied by measuring the polarization-vs-electric field hysteresis loops (P-E loops). The P-E loops illustrated that the coercive field of ACP samples could be further tuned from 1.84 kV/cm to 3.03 kV/cm by changing fACP (0.1–10 Hz). This work demonstrated the enormous potential of ACP optimization in relaxor-PT single crystal-based low-frequency transducer applications. [ABSTRACT FROM AUTHOR]

In this work, the piezoelectric and dielectric properties of [001]-oriented 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 single crystals under alternating current poling (ACP) at different temperatures were studied. The piezoelectric coefficients (d33 ∼ 1930 pC/N, d31 ∼ −850 pC/N) and free dielectric permittivity (εT33/ε0 ∼ 7570) reached their highest values when the poling temperature (Tpoling) was 70 °C. Compared with traditional direct current electric field poling at 20 °C, 70 °C-ACP samples showed an enhancement of 40%, 35%, and 49% for d33, d31, and εT33/ε0, respectively. Meanwhile, d33 and εT33/ε0 were enhanced by about 9% when Tpoling increased from 20 °C to 70 °C under ACP, while d31 remained the same value and the dielectric loss was lowered from 0.29% to 0.22%. Moreover, ACP samples with different Tpoling have similar electromechanical coupling factors (k31 ∼ 0.44, kt ∼ 0.60). A discussion of the mechanism for the ACP enhancement was based on the domain observation using piezoresponse force microscopy, and the results showed that the domain densities of ACP samples with different Tpoling were positively correlated with their piezoelectric properties. This work demonstrated the enormous potential of ACP optimization for relaxor-PT single crystal applications. [ABSTRACT FROM AUTHOR]

Operation at temperatures well above ambient is desired for applications such as smart structures integrated within aircraft and space vehicles. Piezoelectric yttrium calcium oxyborate single crystal YCa4O(BO3)3 (YCOB) was found to exhibit no phase transition until its melting temperature around ∼1500 °C. The temperature characteristics of the resonance frequency, electromechanical coupling, and dielectric permittivity were studied in the temperature range of 30–950 °C for different orientations. The electrical resistivity at 800 °C was found to be greater than 2×108 Ω cm. Together with its temperature independent electromechanical coupling factor (∼12%) and engineered resonance frequency behavior, these make YCOB crystals excellent candidates for sensing applications at ultra high temperatures. [ABSTRACT FROM AUTHOR]