The internal friction (IF) of tantalum and niobium doped with different amounts of oxygen (0.1-0.7 at.%) was studied with an inverted torsion pendulum. With increasing 0 contents we observed in a (1/T)-plot a symmetrical broadening of the IF peak and a shift to slightly higher temperatures. This is in contrast to earlier studies of these alloys in which the existence of 0 agglomeration (pairs, triplets etc.) was suggested from the assumption of an asymmetrical broadening of the IF peak. A physical model to explain these results has to be developed

Ca3Co4O9+δceramic powders were synthesized by the polymerized complex (PC) method. The same Ca3Co4O9+δceramic bar were treated in turn with three different processes of oxygen treatment: with no treatment, with oxydol (H2O2) treatment, and with N2treatment. 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 H2O2treatment and with no treatment, the activation energyHare 1.24 eV and 1.04 eV, respectively, and the preexponential factor τ0are 2.54×10-17sec and 7.82×10-15sec, respectively. We speculate that the mechanical relaxation process occurs in the Ca2CoO3subsystem of Ca3Co4O9+δ. The relaxation process for sample with no treatment is associated with the migration of OVs clusters in Ca2CoO3subsystem, and the relaxation process for the sample with H2O2treatment is associated with the migration of isolated OVs in Ca2CoO3subsystem.

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