Commercial lead-based piezoelectric materials raised worldwide environmental concerns in the past decade. Bi 0.5 Na 0.5 TiO 3 -based solid solution is among the most promising lead-free piezoelectric candidates; however, depolarization of these solid solutions is a longstanding obstacle for their practical applications. Here we use a strategy to defer the thermal depolarization, even render depolarization-free Bi 0.5 Na 0.5 TiO 3 -based 0-3-type composites. This is achieved by introducing semiconducting ZnO particles into the relaxor ferroelectric 0.94Bi 0.5 Na 0.5 TiO 3 -0.06BaTiO 3 matrix. The depolarization temperature increases with increasing ZnO concentration until depolarization disappears at 30 mol% ZnO. The semiconducting nature of ZnO provides charges to partially compensate the ferroelectric depolarization field. These results not only pave the way for applications of Bi 0.5 Na 0.5 TiO 3 -based piezoceramics, but also have great impact on the understanding of the mechanism of depolarization so as to provide a new design to optimize the performance of lead-free piezoelectrics.

High-quality broadband ultrasound transducers yield superior imaging performance in biomedical ultrasonography. However, proper design to perfectly bridge the energy between the active piezoelectric material and the target medium over the operating spectrum is still lacking. Here, we demonstrate a new anisotropic cone-structured acoustic metamaterial matching layer that acts as an inhomogeneous material with gradient acoustic impedance along the ultrasound propagation direction. When sandwiched between the piezoelectric material unit and the target medium, the acoustic metamaterial matching layer provides a broadband window to support extraordinary transmission of ultrasound over a wide frequency range. We fabricated the matching layer by etching the peeled silica optical fibre bundles with hydrofluoric acid solution. The experimental measurement of an ultrasound transducer equipped with this acoustic metamaterial matching layer shows that the corresponding −6 dB bandwidth is able to reach over 100%. This new material fully enables new high-end piezoelectric materials in the construction of high-performance ultrasound transducers and probes, leading to considerably improved resolutions in biomedical ultrasonography and compact harmonic imaging systems.

Phase diagram of Bi 0.5 Na 0.5 TiO 3 -BaTiO 3 -K 0.5 Na 0.5 NbO 3 ternary system has been analyzed and ͑0.94− x͒BNT-0.06BT-xKNN ͑0.15Յ x Յ 0.30͒ ceramics have been prepared and investigated. Pseudocubic structures were confirmed by x-ray diffractions and its preliminary Rietveld refinements. P-E, S-E, and S-P 2 profiles ͑where P, E, and S denote polarization, electric field, and strain, respectively͒ indicate electrostrictive behavior of all ceramics. The compositions with x = 0.20 and 0.25 show pure electrostrictive characteristics. The dissipation energy, electrostrictive strain, and electrostrictive coefficient have been determined and compared with other lead-free and lead-containing electrostrictors. The electrostrictive coefficient can reach as high as 0.026 m 4 / C 2 , about 1.5 times of the value of traditional Pb-based electrostrictors. © 2010 American Institute of Physics. ͓doi:10.1063/1.3491839͔Both electrostrictive and piezoelectric ceramics are commercially used in electromechanical devices, such as actuators, space mirrors, etc. Electrostrictors have special advantages over piezoelectrics, because they do not require poling process and there is negligible hysteresis in strain-electric field ͑S-E͒ cycle, which is important for precision position control. [1][2][3] In electrostriction, the sign of the field-induced deformation is independent of the polarity of the field and is proportional to the square of the applied electric fieldwhere Q is the electrostrictive coefficient and P is polarization. 2 In recent years, a lot of attention has been paid to leadfree piezoelectric materials 4,5 but much less effort was devoted to high-performance lead-free electrostrictors. 6-9 One of the reasons might be due to the much smaller commercial market for high performance electrostrictors than for piezoelectric devices. Another reason might be due to the lack of public awareness on the fact that most of currently used electrostrictors are also lead based materials. With increasing pressure from environmental legislations, lead-free piezoelectric and electrostrictive materials are urgently in demand. Therefore, it is just as important to study lead-free electrostrictive materials as lead-free piezoelectric materials.Electrostriction is a general property of all dielectric materials but it is significantly large in ferroelectrics just above the Curie temperature ͑T c ͒, where an electric field can induce energetically unstable ferroelectric phase. In relaxor ferroelectrics, the electrostrictive strain can be kept at a relatively high level in a wide temperature range, because of the diffused phase transition. 2 If the phase transition temperature of a relaxor ferroelectrics is close to room temperature ͑RT͒, the electrostrictive effect can be very large at RT. Therefore, one may adjust the composition or dopants in lead-free relaxor ferroelectrics to produce pseudocubic/cubic crystal structure at RT, which might produce good lead-free electrostrictors. Recently reported electrostrictors, ͑Sr 1−y−x Na y Bi x ͒Ti...