Piezoelectric single-crystal composites (PSCCs) have been studied and applied because of their improved resolution and power source level performance in underwater acoustic transducer applications relative to traditional piezoelectric ceramic composites (PCCs). Currently, the methods to fabricate curved PSCCs are mostly derived from PCCs, including molding with flexible backing, molding with heating, and molding with the casting rubber method. Unfortunately, the methods mentioned above are not suitable for preparing curved PSCCs for underwater acoustic transducer applications because of their brittleness, the large anisotropy of piezoelectric single crystals, and the high thickness (>2 mm) of PSCCs for achieving the low operating frequency (<700 kHz). In the present work, we proposed a preparation method, 3D-printing-assisted dice and insert technology, and successfully prepared curved PSCCs with high performance. Although the PSCCs have a low volume fraction of single crystals in this work (∼33%), a high thickness electromechanical factor k t of 86% and a large piezoelectric coefficient d 33 of 1550 pC/N were achieved in the curved 1−3 PSCCs, which are superior to other reported PSCCs and PCCs with nearly the same volume fraction of single crystals and piezoelectric ceramics. This work presents a paradigm for fabricating curved PSCCs for underwater acoustic transducers, and this method shows the potential for large-area, special-shaped PSCCs, which are key materials for next-generation underwater acoustic transducers.

Electrodes are critical to piezoelectric single crystal composites (PSCCs) as they directly determine the efficiency and reliability of piezoelectric devices. Currently, a comprehensive comparison of the major properties of different electrodes on PSCCs, particularly their adhesive performance, is highly needed because the cross-linked structure and large surface-displacement fluctuations of PSCCs likely cause the peeling and failure of electrodes. Herein, we compared electronic conductivity and adhesive performance of different electrodes for PSCCs including magnetron sputtering Au (MS Au), electron beam evaporation Au (BE Au), and low-temperature silver paste (LTSP) electrodes. The results demonstrate that the LTSP electrodes exhibited the highest adhesion strength of 3.5 MPa compared to MS Au (2.1 MPa) and BE Au (0.9 MPa) electrodes on PSCCs. In addition, the adhesion strength of electrodes on PSCCs was lower than that on piezoelectric single crystals owing to the existence of the polymer phase. In terms of electrical conductivity, the LTSP electrodes displayed the highest resistivity of 2.25 × 10 −6 Ω•m, and MS Au and BE Au electrodes showed similar resistivities of 6.8 × 10 −8 and 7.6 × 10 −8 Ω•m, respectively. This work provides important information in choosing electrodes for PSCCs, thus benefiting the design for underwater acoustic transducers.

Pb-based relaxor piezoelectric single crystal composites (PSCCs) have attracted widespread attention for improving the bandwidth and sensitivity performance of acoustic transducers due to their excellent electromechanical and piezoelectric properties. Alternating current polarization (ACP) has been proven as an effective method for enhancing the dielectric and piezoelectric properties of relaxor-PbTiO3 single crystals. Herein, we investigated the effects of the amplitude, frequency, and cycle number of the poling electric field on the piezoelectric and dielectric performances of PSCCs and obtained the optimum poling condition of ACP. Compared with the traditional direct current poling method, both the dielectric permittivity (ε33T/ε0) and piezoelectric coefficient (d33) of the AC-poled PSCCs were both increased by up to 20%. Notably, the ACP PSCC with a volume fraction of 60% exhibited a high d33 of 1610 pC/N, which is superior to values previously reported for PSCCs. This work provides an alternative strategy for enhancing the properties of PSCCs and may contribute to the further development of piezoelectric applications.

Large-area and conformal piezoelectric elements are highly desired for acoustic transducers to possess a large power source level and wide detecting range. To date, single-crystal piezocomposites attract much attention on enhancing the power source level and bandwidth for next-generation acoustic transducers, owing to their higher piezoelectric and electromechanical coupling properties compared to traditional piezocomposites. Unfortunately, it is still challenging to achieve large-area and conformal single-crystal piezocomposites because of the fragile nature, large anisotropy, and the limited grown size of piezoelectric single crystals. Here, we successfully fabricate the conformally large-area single-crystal piezocomposite with an area of 160 × 50 mm 2 and a bending angle of 162°by a modified 3D-printingassisted inserting method. The single-crystal piezocomposite exhibits a high thickness electromechanical coupling factor k t of 85% and a large piezoelectric coefficient d 33 of 1150 pC/N, surpassing those of the reported large-area piezocomposites. The influence of the volume fraction and curvature radius of single-crystal PCs and acoustic transducers was investigated. Furthermore, we designed an acoustic transducer based on the conformal single-crystal piezocomposite. Benefiting from the excellent piezoelectric and electromechanical properties of the single-crystal piezocomposite, the transducer indicates a high maximum transmitting voltage response of 171.8 dB. Especially, its bandwidth (−3 dB) achieves 60 kHz with a resonant frequency of 292 kHz, which is about 1.8 times superior to the conformal acoustic transducer based on the ceramic piezocomposite with a similar resonant frequency. This work may benefit the future design and fabrication of high-performance and complex-shape piezoelectric composites as key materials for next-generation transducers.