Mn modified rhombohedral Pb(In_0.5Nb_0.5)O₃-Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PIN-PMN-PT:Mn) single crystals poled along [011]_C crystallographic direction exhibit a “2R” engineered domain configuration, with macroscopic mm2 symmetry. The complete sets of material constants were determined using combined resonance and ultrasonic methods, and compared to [001]_C poled PIN-PMN-PT:Mn crystals. The thickness shear piezoelectric coefficient d₁₅ and electromechanical coupling factor k₁₅ were found to be on the order of ∼3000 pC/N and 0.92, respectively, with longitudinal piezoelectric coefficient d₃₃ and coupling factor k₃₃ being on the order of ∼1050 pC/N and 0.90. Of particular importance is that PIN-PMN-PT:Mn single crystals exhibited high mechanical quality factor Q₃₃ ∼ 1000, comparable to “hard” PZT8 ceramics, which can also be confirmed by the low extrinsic contribution, being ≤2% from the Rayleigh analysis.

A high quality orthorhombic (K, Na, Li)(Nb, Ta)O₃ single crystal with a large size of 9 × 9 × 11 mm³ was successfully grown using the top-seeded solution growth method. Its large size allowed us to perform comprehensive investigation on this crystal. A complete set of elastic, dielectric and piezoelectric coefficients was determined using combined resonance and ultrasonic methods. The longitudinal piezoelectric coefficient d₃₃ and the transverse piezoelectric coefficient d₃₁ of this lead-free piezoelectric single crystal are as high as 354 pC N⁻¹ and −163 pC N⁻¹, respectively, which are two times higher than those of KNN-TL ceramics and are comparable with those of PZT5. The electromechanical coupling factor k₃₃ is as high as 82%, much higher than those of KNN-TL ceramics and PZT5. The coefficient d_33,strain was found to be as high as 672 pm v⁻¹ and the extrinsic contribution (~22%) was investigated by Rayleigh analysis. These high piezoelectric properties make this single crystal a promising candidate for replacing lead-based piezoelectric materials.

Mn modified 0.26Pb(In_1/2Nb_1/2)O₃−0.42Pb(Mg_1/3Nb_2/3)O₃−0.32PbTiO₃ (PIN-PMN-PT:Mn) single crystals with orthorhombic perovskite crystal structure were polarized along [011] direction, resulting in the single domain state “1O.” The complete set of material constants was determined using the combined resonance and ultrasonic methods. The thickness shear piezoelectric coefficient d₁₅ and electromechanical coupling factor k₁₅ were found to be on the order of 3100 pC/N and 94%, respectively, much higher than longitudinal d₃₃ ∼ 270 pC/N and k₃₃ ∼ 70%. Using the single domain data, the rotated value of d₃₃* along [001] direction was found to be 1230 pC/N, in agreement with the experimentally determined d₃₃ value of 1370 pC/N, conferring extrinsic contributions being about 10%, which was also confirmed using the Rayleigh analysis. In addition, the mechanical quality factors Q_m were evaluated for different “1O” vibration modes, where the longitudinal Q_m was found to be ∼1200, much higher than the value for “4O” crystals, ∼300.

The piezoelectric properties of the PZT-5H ceramics under various polarization conditions are compared and analyzed. It is worth noting that compared to direct current polarization, the piezoelectric coefficient (d₃₃), free dielectric constant (${\epsilon }_{33}^{\mathrm{T}}$ /${\epsilon }_0$ ), and electromechanical coupling coefficient (k_t) of the PZT-5H ceramics under alternating current polarization (ACP) have increased by 10.7%, 15.9%, and 15.4%, respectively. According to the analysis of the domain distribution patterns in the [001] surface of the PZT-5H ceramics under the two polarization conditions measured using a piezoresponse force microscope, the ACP makes the piezoelectric material have a high density of the domain wall, which greatly enhances its piezoelectric performance. This work provides an effective means to improve the piezoelectric properties of PZT-5H ceramics and will be of great significance to piezoelectric applications using this type of piezoelectric ceramic.

High-performance broadband ultrasound transducers provide superior imaging quality in biomedical ultrasound imaging. However, a matching design that perfectly transmits the acoustic energy between the active piezoelectric element and the target medium over the operating spectrum is still lacking. In this work, an anisotropic gradient acoustic impedance composite material as the matching layer of an ultrasonic transducer was designed and fabricated; it is a non-uniform material with the continuous decline of acoustic impedance along the direction of ultrasonic propagation in a sub-wavelength range. This material provides a broadband window for ultrasonic propagation in a wide frequency range and achieves almost perfect sound energy transfer efficiency from the piezoelectric material to the target medium. Nano tungsten particles and epoxy resin were selected as filling and basic materials, respectively. Along the direction of ultrasonic propagation, the proportion of tungsten powder was carefully controlled to decrease gradually, following the natural exponential form in a very narrow thickness range. Using this new material as a matching layer with high-performance single crystals, the −6 dB bandwidth of the PMN-PT ultrasonic transducer could reach over 170%, and the insertion loss was only −20.3 dB. The transducer achieved a temporal signal close to a single wavelength, thus there is the potential to dramatically improve the resolution and imaging quality of the biomedical ultrasound imaging system.