Structure investigation and thermoelectric properties of [Ca₂CoO₃][CoO₂]_1.61 based p-type materials

Oxide-based thermoelectric materials are being considered for applications in both power generation and energy recovery from waste heat. Among them, transition metal oxide [Ca₂CoO₃][CoO₂]_1.61 has demonstrated to be one of the most promising high-temperature (800-1000k) thermoelectric candidates. The crystal structure of [Ca₂CoO₃][CoO₂]_1.61 consists of two subsystems: a distorted rock-salt-type [Ca₂CoO₃] (RS) layer sandwiched between two hexagonal Cdl2 type [CoO₂] (H) layers stacked along the c-axis. The two subsystems share common lattice parameters a, c but a misfit along b-axis leading to an incommensurately modulated structure. In present study, the influence of cation doping on the thermoelectric properties of [Ca₂CoO₃][CoO₂]_1.61 was studied by the evolution of crystal structure with the combination of synchrotron powder diffraction and X-ray absorption near-edge spectroscopy. In addition, the influence of sample density and measuring atmosphere on the carrier transports properties was also studied.