Fig. 2: Preparation and characterization of transparent PIN-PMN-PT crystals.

a Illustration of the transparency enhancement process via a.c. poling. The domain structures were characterized by scanning electron microscopy (SEM, upper figure) from the (100) surface and birefringence imaging microscopy (BIM, below the SEM figure) from the (001) surface. The 71^o domain wall (DW) and 109^o DW are indicated by the orange and red arrows in SEM figures, respectively. The colors in BIM images reveal the orientation angles (φ) of the projection of the principal optical axis of the ferroelectric domains on the (001) plane. Specifically, the blue and red colors represent the projection of the principal optical axis along the diagonal faces on the (001) plane, that is, φ of 45° and 135°, respectively. b Photo of a.c.-poled PIN-PMN-PT, LN, and traditional d.c.-poled PIN-PMN-PT crystals. c Piezoelectric coefficients (d₃₃) of PIN-PMN-PT crystals poled by various amplitudes of a.c. electric field. d d₃₃ with respect to cycle number of a.c. electric field. e d₃₃ with respect to frequency of a.c. electric field. f Comparison of piezoelectric and dielectric properties of a.c.-poled PIN-PMN-PT and LN crystals. g Simulated electric impedance (at 34 MHz) of the PIN-PMN-PT- and LN-based transducers as a function of the aperture size. h Simulated peak-to-peak amplitude of pulse-echo response for the PIN-PMN-PT- and LN-based transducers with different aperture sizes. The pulse-echo amplitudes were normalized by the maximum amplitude of the PIN-PMN-PT-based transducer.