Oxygen Vacancy Relaxation in Ca<sub>3</sub>Co<sub>4</sub>O<sub>9+δ</sub> Ceramics

Abstract

Ca 3 Co 4 O 9+δ ceramic powders were synthesized by the polymerized complex (PC) method. The same Ca 3 Co 4 O 9+δ ceramic bar were treated in turn with three different processes of oxygen treatment: with no treatment, with oxydol (H 2 O 2 ) treatment, and with N 2 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 H 2 O 2 treatment and with no treatment, the activation energy H are 1.24 eV and 1.04 eV, respectively, and the preexponential factor τ 0 are 2.54×10 -17 sec and 7.82×10 -15 sec, respectively. We speculate that the mechanical relaxation process occurs in the Ca 2 CoO 3 subsystem of Ca 3 Co 4 O 9+δ . The relaxation process for sample with no treatment is associated with the migration of OVs clusters in Ca 2 CoO 3 subsystem, and the relaxation process for the sample with H 2 O 2 treatment is associated with the migration of isolated OVs in Ca 2 CoO 3 subsystem.