Substitution effects on the structural and magnetic behaviour of Na0.63CoO2

Abstract

This paper discusses the effects of cation substitutions on the structural (and linked electronic) transition which has been observed in Na_0.63CoO₂. The effects of the following substitutions are reported: Ca on the Na site; Fe and Ni on the Co site. Ca doping suppresses the transition and is suggested to interfere with the Na ordering and hence causes a variation in the electronic structure. Fe and Ni doped samples all show transitions, but the transition temperature decreases with the dopant cation concentration. This implies that the replacement of Co by Fe and Ni may enhance the instability in the low-temperature regime. The influence of the substitution is also reflected in the structure and magnetic behaviour of the doped samples.