Microstructure and thermoelectric performance of La‐doped (Ca_0.9Ag_0.1)₃Co₄O₉/nano‐sized Ag composite ceramics

Abstract

Ca 0.9-x Ag 0.1 La x ) 3 Co 4 O 9 /nano-sized Ag thermoelectric composite ceramics were fabricated by solid-state reaction method. The influences of La 3+ dopants on the microstructure, band gaps, and thermoelectric properties were investigated. X-ray photoelectron spectroscopy fitting results showed that the reduction of oxygen vacancy and the increment of trivalent cobalt concentration could significantly improve thermoelectric performance. With the increasing of La 3+ dopants level, the band gaps of samples enlarged. Electrical resistivity decreased from 21.3 to 17.2 mΩ·cm, while Seebeck coefficient increased from 113.3 to 182.3 μV/K. Furthermore, the peak ZT value of 0.18 was obtained at 1073 K for the x = 0.03 sample, resulting from the lower thermal conductivity of 1.05 W/(m·K). The obtained results suggest that the La 3+ substitution, oxygen vacancy, and Ag inclusions can dramatically improve the thermoelectric performance of Ca 3 Co 4 O 9 composites. K E Y W O R D S (Ca 0.9-x Ag 0.1 La x ) 3 Co 4 O 9 , electrical conductivity, nano-sized Ag, thermoelectric composites 8 | SHI et al.

Exfoliation of Ca3Co4O9 to Two-Dimensional Single-Crystalline Misfit Calcium Cobaltates for Energy Storage Applications

“…Figure S5a,b in the Supporting Information shows the XPS wide spectra for CCO-B and CCONS where the binding energy peaks located at 349.6, 780.2, and 530.6 eV correspond to Ca 2p, Co 2p, and O 1s, respectively. The oxidation state of cobalt in CCO-B (Ca 2 CoO 3 –CoO 2 ) is a topic of controversy, with various researchers utilizing different approaches to deconvolute the Co 2p 3/2 peak in CCO-B. ,− Here, we have deconvoluted the Co 2p 3/2 peak based on several measurements found in the existing literature on CCO-B, including magnetic studies and X-ray absorption studies. ,,− In CCO-B, both cobalt atoms in the Ca 2 CoO 3 and CoO 2 layers are situated in an octahedral coordination environment. The cobalt atoms in the Ca 2 CoO 3 layer have a +3 oxidation state, while those in the CoO 2 layer exhibit a mixed oxidation state, including both +3 and +4 states .…”