Fig. 1.

Structural characterization and piezoelectric properties of BTO NPs. (A) XRD pattern of t-BTO NPs and the enlarged region in the red dot circle. (B) SEM image and the size distribution (inset) of t-BTO NPs. (C) TEM image of t-BTO NPs. (D) HRTEM image of t-BTO NPs and corresponding SAED pattern showing in the inset. (E) EDX surface-scan element distribution of Ba, Ti and O of t-BTO NPs. (F) Raman spectra of t-BTO NPs. (G, H) Height, piezoelectric amplitude and phase images of t-BTO NPs (G) and c-BTO NPs (H). (I, J) Amplitude loop curve and phase loop curve of c-BTO NPs (I) and t-BTO NPs (J) at an ac voltage from −4 V to 4 V. (K) The polarization-electric field (P–E) hysteresis curves of c-BTO NPs and t-BTO NPs. (L) COMSOL simulation of the piezopotential generated by one single t-BTO NP under varied US intensities. Inset displays the piezopotential distribution under 2 W cm⁻² US stimulation.