Synthesis and structural properties of thermoelectric Ca3-xAgxCo4O9+delta powders

摘要

A series of Ca3-xAgxCo4O9+delta (0 <= x <= 0.2) powders is prepared by the Pechini sol-gel method. The effect of dispersants on the size and morphology of the Ca2.9Ag0.1Co4O9+delta powders is investigated. The desired powders are obtained after calcinations of the dried powders at 800 degrees C for 12 h. The structural and morphological properties are studied with the help of XRD patterns, FE-SEM images, FT-IR spectra, Raman spectra, and XPS spectra. It is found that a mixed valence (+ 3 and + 4) of Co exists in a CdI2-type CoO2 layer, while a mixed valence (+ 2, + 3, and + 4) exists in the CoO of a rock salt-type Ca2CoO3 layer. The mixed-valence state in the CoO2 layer can improve the high-temperature thermoelectric properties of Ca3Co4O9 systems.