2D porous nanosheets of Y-doped ZnO for dielectric and ferroelectric applications

Abstract

Ferroelectricity in pure ZnO nanocrystals is an unlikely physical phenomenon. Here, we show origin of high temperature ferroelectricity in ZnO as a result of yttrium (Y) doping. First, we briefly introduced the wet chemical synthesis of pure and yttrium (Y) doped ZnO nanocrystals. The crystalline phase and morphological appearance of as synthesized pure and Y-doped ZnO nanocrystals were examined using powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. By Y-doing, the morphology of ZnO crystals evolved from 1D nanopencil (pure ZnO) to 3D flower-like architectures assembled by 2D porous nanosheets (Y-ZnO). Crystallite size, deformation stress, energy density and lattice strain of both the nanoparticles were evaluated using Scherrer and Williamson-Hall methods. Frequency as well as temperature dependence of dielectric constant, dielectric loss and ac conductivity of Y-doped ZnO nanosheets were investigated. Ferroelectricity in Y-doped ZnO nanosheets was established using the temperature dependent curve of dielectric constant and the room temperature polarization hysteresis loop. The temperature dependent curve of dielectric constant displayed a ferroelectric to paraelectric transition peak at 138 °C. The Y-ZnO nanosheets exhibit weak ferroelectric polarization hysteresis loop with a remnant polarization (Pr) of 0.09 µC/cm2 and a coercive field (Ec) of 5.87 kV/cm (@ RT). The nature of the leakage present in Y-ZnO sample was extracted from the time-dependent compensasted (TDC) hysteresis study. Leakage current density was found to decrease due to Y-doping in ZnO nanocrystals.