Suppressed spin-density-wave transition and enhanced electrical conductivity in chlorine doped Ca3Co4O9−xClx ceramics

The structural, magnetic, electrical and thermal transport properties of the Cl-doped Ca3Co4O9−xClx (x = 0, 0.225, 0.45, 0.675, 0.9) ceramics have been investigated systematically. The degree of orientation of grains increases with increasing Cl-doping content. Obvious shoulder is observed in the dχ−1(T)/dT versus T curve for the Cl-doped samples and the shoulder shifts to lower temperature as Cl-doping content increases, indicating the long-range spin-density-wave state becomes unstable in these Cl-doped samples. Cl-doping also has a suppression effect on the ferrimagnetic state. The resistivity ρ of the Cl-doped samples is lower than that of Ca3Co4O9 in whole measured temperature range, which is suggested to be related to the increased carrier mobility induced by Cl-doping. The power factor P of the x = 0.9 sample is about 1.6 times larger and ZT is 1.3 times larger than that of the un-doped sample Ca3Co4O9.

► Present a new way to investigate the thermoelectric properties of layered cobaltite.
► Obvious shoulder is observed in the dχ−1(T)/dT versus T curve for the Cl-doped samples.
► Cl-doping has a negative effect on the ferrimagnetic state.
► The resistivity ρ of the Cl-doped samples is lower than that of Ca3Co4O9 in whole measured temperature range.
► Both the power factor P and the dimensionless figure of merit ZT increase as Cl doped into the system.