Evolution of microstructure, defect, optoelectronic and magnetic properties of Cu1-xCaxFeO2 ceramics

Abstract

Microstructures, defect characteristics, optoelectronic, and magnetic properties of polycrystalline delafossite Cu1-xCaxFeO2 (x = 0.00–0.08) samples have been systemically investigated. Our investigation results distinctly show that divalent Ca2+ ions can successfully substitute partial Cu+ ions and prompt the grain size and induce the partial Fe3+ valence variation to Fe2+. The positron annihilation lifetime spectra signifies that the cation vacancy clusters exist in all samples, the size and concentration of vacancy defects are redistributed with increasing Ca2+ ions content, while the overall defect environment of CuFeO2 system is not changed. The Hall-effect measurement results indicate the transition of semiconductor type from p-type to n-type. The UV–Visible absorption spectroscopy results indicate that the calculated band gap of the prepared samples is estimated to be 3.42–3.58 eV, indicating the series can be applied to the transparent conductive oxide materials. The magnetic measurements reveal that the transition temperature TN1 and TN2 are independent of Ca2+ content x, while the coexistence of antiferromagnetism and weak ferromagnetism for all the doped samples are observed. A moderate Ca2+ content, i.e. x = 0.02, can distinctly promote weak ferromagnetism. The above internal mechanism is probably relevant to the evolution of lattice structure and defect characteristics caused by Ca2+ ions doping.