Dielectric anomalous peaks accenting ferroelectricity prospects of Li and Mg co-doped ZnO ceramics

Abstract

This paper presents effects of lithium (Li) and magnesium (Mg) dopants on the dielectric properties of ZnO ceramics with emphasis on ferroelectricity prospects of co-doped samples with Zn0.7Li0.28Mg0.02O compositions. Ceramics with average relative density ∼97% were produced by solid-state-reaction of mechanically activated powder precursors using 1000 °C for 2 h sintering conditions. Room temperature A.C. conductivity σa.c(ω) and temperature-frequency (T-ω) dependence of dielectric permittivity (ε′) and loss (ε″) of the samples are measured within temperature range from −100 to 150 °C in air and in a vacuum cryostat with liquid nitrogen coolant. Undoped ZnO σa.c(ω) data exhibits a nearly insensitive dependence to the ω while that of doped samples show significant ω dependence and higher σa.c(ω) values than undoped ZnO ceramics. Anomalous ε′ and ε″ peaks were observed in Zn0.7Li0.28Mg0.02O specimens around TC of −25 °C during cooling and −10 °C during heating measurements in air. However, dielectric properties of the same Zn0.7Li0.28Mg0.02O ceramics obtained in vacuum cryostat and from undoped ZnO ceramics in air and in vacuum cryostat did not reveal any ε′ and ε″ transition peaks at low temperature.