Thermally stimulated depolarization current (TSDC) measurements were carried out on 0.1% and 1% iron (Fe)‐doped SrTiO3 crystals to study various effects that are not detected from other electrical characterization methods such as impedance spectroscopy. Using this TSDC technique, the origins of different relaxations in Fe‐doped SrTiO3 crystals were identified, and activation energy of the orientated dipole, energy depth of trap site, and trap density in the polarized samples were then estimated from TSDC measurements. From the resulting activation energy of 0.65±0.08 eV of trap charges, these traps are assigned to oxygen vacancy‐iron defect complexes. The high‐temperature peak at temperature ∼190°C is assigned to the relaxation current of oxygen vacancies and the calculated activation energy of 0.91±0.05 eV is in good agreement with the literature data.

Based on growing evidence linking autophagy to preconditioning, we tested the hypothesis that autophagy is necessary for cardioprotection conferred by ischemic preconditioning (IPC). We induced IPC with three cycles of 5 min regional ischemia alternating with 5 min reperfusion and assessed the induction of autophagy in mCherry-LC3 transgenic mice by imaging of fluorescent autophagosomes in cryosections. We found a rapid and significant increase in the number of autophagosomes in the risk zone of the preconditioned hearts. In Langendorff-perfused hearts subjected to an IPC protocol of 3×5 min ischemia, we also observed an increase in autophagy within 10 min, as assessed by Western blotting for p62 and cadaverine dye binding. To establish the role of autophagy in IPC cardioprotection, we inhibited autophagy with Tat-ATG5 K130R , a dominant negative mutation of the autophagy protein Atg5. Cardioprotection by IPC was reduced in rat hearts perfused with recombinant Tat-ATG5 K130R . To extend the potential significance of autophagy in cardioprotection, we also assessed three structurally unrelated cardioprotective agents-UTP, diazoxide, and ranolazine-for their ability to induce autophagy in HL-1 cells. We found that all three agents induced autophagy; inhibition of autophagy abolished their protective effect. Taken together, these findings establish autophagy as an end-effector in ischemic and pharmacologic preconditioning.

Thermally stimulated depolarization current (TSDC) measurements were carried out on degraded SrTiO3 crystals and ceramics to investigate the relationship between depolarization effects and degradation phenomena. Using this technique, the origins of dielectric relaxations in Fe‐doped SrTiO3 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 1014 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.