Impact of Li doping on the microstructure, defects, and physical properties of CuFeO2 multiferroic ceramics

Abstract

An investigation on the microstructure, defects, and physical properties for Cu1-xLixFeO2 (x = 0.00–0.08) ceramic samples is here presented. The delafossite structure with R3‾m space group for all samples is retrieved using Powder X, whereas the grain growth can be effectively inhibited by Li doping. Positron annihilation results demonstrate that the vacancies are formed in all specimens, defect size and concentration can be effectively affected by Li doping. Electric properties measurements show that all the prepared samples exhibit giant dielectric behavior, while the undoped CuFeO2 sample exhibits maximum value around 3.5 × 104. The internal barrier capacitance model (IBLC) can be used to systematically explain the dielectric mechanism of CuFeO2 system. Optical analysis shows that an obvious absorption peak occurs at around 225 nm, and a decrease of direct optical band gap with the increase in Li doping content is observed. Magnetic properties measurements reveal that the antiferromagnetic transition temperature has almost no change with the increase in Li content, and that the co-existence of ferromagnetism and antiferromagnetism is observed. The magnetization increases with the Li doping amount, in which the x = 0.08 sample exhibits the maximum magnetization (about 24 emu/g). The evolution of magnetic properties is seen to be related to lattice distortion, vacancy defect, and disturbance of the spin structure induced by Li doping.