3D hierarchical Ho-doped ZnO micro-flowers assembled with nanosheets: A high temperature ferroelectric material

Abstract

A novel high temperature ferroelectric (Tc ∼205 °C, Ec ∼4.72 kV/cm & Pr ∼0.05 μC/cm2) marigold-like holmium (Ho)-doped ZnO nanocrystals were developed using wet chemical co-precipitation method. Herein, we have studied the impact of Ho-doping on structural, morphological, dielectric and ferroelectric properties of ZnO nanocrystals. Interestingly as a result of Ho-doping, the 1D nanopencils (NPCs) of pure ZnO were transformed to 3D hierarchical micro-flowers made up of nanosheets (NSs). Crystallite size (L), deformation stress (σ), energy density (u) and lattice strain of both nanopencils and nanosheets were evaluated using the Scherrer equation and Williamson-Hall methods. The temperature dependent plot of dielectric constant (ε′) displayed a (dielectric anomaly) ferro-to para-electric transition peak at 205 °C. The flower-like Ho-doped ZnO nanosheets exhibit a weak ferroelectric polarization hysteresis characteristic with a coercive field (Ec) of 4.72 kV/cm and a remnant polarization (Pr) of 0.05 μC/cm2 at room temperature. Electric conduction properties were studied for both pure ZnO NPCs and Ho-doped ZnO NSs. Our study opens up the door of inducing high temperature ferroelectric switching characteristics in bio compatible pristine ZnO nanostructures by doping it with rare earth holmium (Ho3+) and to use the ferroelectric material in designing components for memory applications.