Figure 2 Structural characterization of LiNbO 3 . (a) Rietveld analysis of neutron diffraction patterns of LiNbO3. The red dots represent the observed intensity. PI3K inhibitor The black lines represent the calculated intensity. The blue line corresponds to the difference between the observed and calculated intensities. The green line shows the Bragg reflection. In the inset of (a), we show the crystal structure of LiNbO3. (b) Field-emission scanning electron

microscopy (FE-SEM) and (c) high-resolution transmission electron microscopy (HR-TEM) images of LiNbO3. In the inset of (c), we show a medium-resolution TEM image of a LiNbO3 nanowire. Figure  2b,c shows FE-SEM and HR-TEM images of LiNbO3, respectively. All of the LiNbO3 samples had nanowire morphology, with a high aspect ratio of 160 to 600 (width 100 to 250 nm; length 40 to 60 μm). selleck inhibitor Note that the LiNbO3 nanowires, synthesized using the molten salt method, had a relatively short length (<10 μm) [21]. The clear lattice fringe indicated the single-crystalline quality of the LiNbO3 nanowires. Based on the

Rietveld analysis, the LiNbO3 nanowires appeared to grow along the [1–10] direction. To investigate the piezoelectricity of the LiNbO3 nanowires, we used PFM. Figure  3a,b,c shows the topography, amplitude, and phase of the piezoelectric response of a single LiNbO3 nanowire, respectively. The brightness of the amplitude map represents the strength of the piezoelectric response; the contrast of the phase map corresponds to the direction of the electric polarization in the nanowire. From Figure  3b,c, the piezoelectric domains in the LiNbO3 HSP90 nanowire were clearly evident. Figure 3 Piezoelectricity/ferroelectricity of the LiNbO 3 nanowire. (a) Topography, (b) piezoelectric amplitude, and (c) piezoelectric phase for a LiNbO3 nanowire. Applied voltage dependences of (d) piezoelectric amplitude and (e) piezoelectric phase. Figure  3d,e shows the switching of the piezoelectric/ferroelectric amplitude and phase with the application of direct-current (dc) voltage.

An abrupt change in the phase suggests the switching of domains in LiNbO3, which is generally associated with ferroelectric behavior [22]. We estimated the piezoelectric coefficient d 33 value from the linear portion of the piezoresponse amplitude signal as approximately 25 pmV-1. After confirming the piezoelectricity/ferroelectricity of the LiNbO3 nanowire, we fabricated a composite nanogenerator for the e 33 and e 31 geometries, as schematically shown in Figure  4a,c, respectively. Even though the LiNbO3 nanowires were randomly distributed inside the PDMS polymer, the piezoelectric/ferroelectric domains could be vertically aligned after applying a strong electric field for poling.