Room temperature synthesis and multiferroic response of Li co-doped (Zn, Co)O nanocrystallites

Abstract

We have chemically synthesized Li-doped ZnO and Li co-doped (Zn, Co)O nano-crystallites following a wet chemical sol-gel route. In the structural characterization, we have performed X-ray diffraction (XRD) analysis, which reveals the presence of an impurity free phase. The particle sizes have been calculated utilizing the Scherrer formula which turns out to be lying in the range of 20–24 nm and 30–34 nm for Li-doped ZnO and Li co-doped (Zn, Co)O nanoparticles, respectively which is also confirmed by TEM (Transmission Electron Microscope) micrographs. In the temperature dependent dielectric measurements (which is the main novelty of this work), no phase transitions are observed for un-doped ZnO and also with Li doping up to 2% concentration, but at higher doping concentrations a typical ferroelectric phase transition is observed around 310 K. The frequency dependent dielectric properties show that irrespective of Li concentration, real and imaginary parts of dielectric constant as well as tangent losses show a decreasing trend. In Zn0.96−yCo0.04LiyO samples, we observed that the values of dielectric constant are greatly decreased by the Co-doping. The magnetic characterization displays a diamagnetic behavior of pure ZnO as well as ZnLiO doped samples, while in the Li-doped (Zn, Co)O samples a ferromagnetic trend is observed, achieving a multiferroic response in our samples. In the UV–Vis spectral studies, we observe that the Li-doping (up to 10%) doesn't affect the direct energy band gap of ZnO considerably. Whereas, the band gap of Zn0.95−yCo0.05LiyO display a declining tendency with increasing Li concentrations.