Thermally Stimulated Relaxation in Fe‐Doped SrTiO 3 Systems: II. Degradation of SrTiO 3 Dielectrics

Thermally stimulated depolarization current (TSDC) measurements were carried out on degraded SrTiO 3 crystals and ceramics to investigate the relationship between depolarization effects and degradation phenomena. Using this technique, the origins of dielectric relaxations in Fe‐doped SrTiO 3 crystals and ceramics have been verified; the physical origins of relaxation mechanisms were later linked to the transient leakage behavior of the samples undergoing degradation from oxygen vacancy migration. In the course of degradation in a single crystal system, the migration of oxygen vacancies , , and the build‐up of an internal bias are detected through the TSDC measurements on samples with different degradation levels. Using a curve fitting method, trap charge concentration on the order of 10 14 cm −3 is obtained in the single crystal system. Other than those relaxation mechanisms identified in the single crystal system, extra relaxation mechanism was found in the polycrystalline systems and was attributed to the relaxation of oxygen vacancies across grain boundaries. Using the initial rise method, the activation energies estimated for the relaxation of defect dipoles, the in‐grain oxygen vacancies pile up at grain boundaries, and relaxation of oxygen vacancies across grain boundaries are 0.73±0.03, 0.86±0.07, and 1.1±0.09 eV, respectively. An ionic demixing model is applied to account for the evolution of TSDC spectra and to bridge changes to the leakage behavior of the degraded samples. In the case of the polycrystalline system, it is suggested that a strong degradation to the insulation resistance occurs when oxygen vacancies migrate across grain boundaries and start to pile up at the cathode region of metallic electrodes. Before that point, the vacancies accumulate at partial blocking grain boundaries in each of the crystallites.