ANELASTIC RELAXATION OF PROTONIC DEFECTS IN ND-DOPED BACEO3

The internal friction technique has been employed to study the interaction of protons with other defects in 2, 3 and 5% Nd-doped BaCeO3. The compounds, after saturation with protons, give rise to two broad anelastic relaxation peaks near 340 K and 273 K at 5800 Hz, with activation energies centered at 0.63 and 0.51 eV, respectively. Using defect symmetry arguments, it will be established that the 273 K peak results from the reorientation of Nd-OH pairs, while the 340 K peak is probably due to the relaxation of higher order Nd-OH clusters. These results show for the first time that protons are associated with dopants in BaCeO3. The relaxation strength is found to depend on the square of dopant concentration. Thermodynamic analysis reveals that the amount of associated protons which produce the relaxation peaks makes up only less than 10% of total;proton concentration. In contrast, no anelastic relaxation peak has been detected in off-stoichiometric A(3)(Ca1+xNb2-x)O-9-delta. Therefore, creating negative charges by off-stoichiometry produces a different defect structure for protons than when dopants are introduced. In other words, the presence of dopants is essential for protons to produce anelastic relaxation in perovskite-type oxides.