Fig. 1.

Microstructure and mechano-electrical properties of P-BTO nanoparticles. (a) TEM images & HRTEM images (insert) of P-BTO nanoparticles. The lattice spacings were 0.399 and 0.402 nm for the (100) and (001) planes of the tetragonal phase, respectively. (b) XRD patterns of P-BTO nanoparticles and the enlarged (002) and (200) peaks around 2θ = 45° (insert). Standard JCPDS of PDF#75-0462 corresponds to the tetragonal BaTiO₃ structure. (c) PFM amplitude curve and phase curve of P-BTO nanoparticles when applying a ramp voltage from −10 to 10 V at room temperature. (d) Digital source meter records of the open-circuit voltages of U-BTO and P-BTO nanoparticles under the same LIPUS (1 MHz, 1.0 W/cm²). The x-axis refers to the time axis of signal recording. The on/off sign represents the time period of LIPUS on/off. (e) COMSOL simulation of piezoelectric potential distribution in U-BTO and P-BTO nanoparticles under the same pressure. The red arrow represents the vector of the spatial electric field formed by the piezoelectric potential difference between the upper and lower surfaces under the action of the external force field. These results indicated that the tetragonal phase P-BTO nanoparticles exhibited desirable piezoelectricity, which could generate wireless electrical stimulation with high efficiency.