Ferroelectricity in Undoped ZnO Nanorods

Abstract

The technological interest in developing novel
\nfunctional nano-objects that exhibit new properties arising
\nfrom their nanoscopic nature is undoubtful. Although bulk
\nZnO is considered to be non-ferroelectric, herein, the
\nferroelectric behavior of undoped and self-standing ZnO
\nnanoparticles is reported for the first time. The nanoparticles
\n(NPs) under study are synthesized by an organometallic
\napproach. When dispersed in a PMMA dielectric matrix, clear
\npolarization loops and antisymmetric switching currents are
\nrecorded for the NPs with the larger volume, in coherence with
\nthe significant polar response of these NPs in solution,
\nmeasured by polarization-resolved second harmonic scattering
\nexperiments. Structural characterizations reveal that ferroelectricity is related to the appearance of a new hexagonal
\ncrystalline phase, its unit cell being swelled with respect to the well-known wurtzite ZnO cell. The volume fraction of this new
\nphase, the polar SHS response, and the amount of ferroelectric polarization response are all linearly linked, underlining the
\nconsistency between these complementary physical characterizations.