Oxygen Vacancy Relaxation in Ca₃Co₄O_9+δ Ceramics

Abstract:

Ca₃Co₄O_9+δ ceramic powders were synthesized by the polymerized complex (PC) method. The same Ca₃Co₄O_9+δ ceramic bar were treated in turn with three different processes of oxygen treatment: with no treatment, with oxydol (H₂O₂) treatment, and with N₂ treatment. Dynamic mechanical analysis (DMA) was performed from 123 to 623 K at rate of 1 K/min while the measuring frequencies are 0.05, 0.1, 0.25, 0.5, 1, 2, and 5 Hz. Two internal friction peaks are observed: one at the temperature range from 360 to 400 K (a broad peak, peak 1) and the other at around 390 K (a sharp peak, peak 2). Peak 2 is in correspondence with sudden metal-semiconductor transition (MST) near 400 K. Peak 1 is a kind of internal friction relaxation peak. For the sample with H₂O₂ treatment and with no treatment, the activation energy H are 1.24 eV and 1.04 eV, respectively, and the preexponential factor τ₀ are 2.54×10^-17 sec and 7.82×10^-15 sec, respectively. We speculate that the mechanical relaxation process occurs in the Ca₂CoO₃ subsystem of Ca₃Co₄O_9+δ. The relaxation process for sample with no treatment is associated with the migration of OVs clusters in Ca₂CoO₃ subsystem, and the relaxation process for the sample with H₂O₂ treatment is associated with the migration of isolated OVs in Ca₂CoO₃ subsystem.

• Periodical: Solid State Phenomena (Volume 184)
• Pages: 98-103
• DOI: https://doi.org/10.4028/www.scientific.net/SSP.184.98
• Online since: January 2012
• Authors: G.C. Lin, H. Liu, J.X. Zhang
• Keywords: Misfit-Layered Cobaltates, Oxygen Vacancy, Relaxation, Thermoelectric Oxides

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