Cr6+ ion doping effects in layered Ca3Co4O9 system

Abstract

The effects of Cr doping on structural, magnetic, electrical and thermal transport properties of Ca3Co4−xCrxO9 (0⩽x⩽0.3) have been investigated systematically. Based on the analysis of X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) data, the Cr ions are suggested to be doped at Co4+-sites in CoO2 layers in the form of Cr6+. The introduction of the nonmagnetic Cr6+ ions results in the decrease of the average effective magnetic moment, which confirming that the ferrimagnetic state of Ca3Co4O9 system can be well suppressed by Cr doping. The magnitude of resistivity and the metal–insulator-transition temperature increase monotonously with increasing x, indicating the enhanced carrier localization and the more stable spin-density-wave state in these Cr-doped samples. As Cr6+ ions are doped into system, the thermopower increases obviously. Correspondingly, the room-temperature thermopower reaches the maximum value of 140μV/K for x=0.3 sample. These results of magnetism and electrical/thermal transport are mainly originated from the variations of carrier concentration and electronic correlation resulted from the partial substitution of Cr6+ for Co ions.