Piezoresponse force microscopy (PFM) was used to investigate the
ferroelectric properties of sol-gel derived LiNbO3 nanoparticles. To
determine the degree of ferroelectricity we took large-area images and
performed statistical image-analysis. The ferroelectric behavior of single
nanoparticles was verified by poling experiments using the PFM tip. Finally we
carried out simultaneous measurements of the in-plane and the out-of-plane
piezoresponse of the nanoparticles, followed by measurements of the same area
after rotation of the sample by 90∘ and 180∘. Such
measurements basically allow to determine the direction of polarization of
every single particle