ELECTRONIC AND IONIC TRAPPING AT DOMAIN-WALLS IN BATIO3

We have coupled electron paramagnetic resonance (EPR) and polarization -voltage measurements to understand the effects of reducing ambients o n the remanent polarization and density of paramagnetic centers in BaT iO3 single crystals. Two types of reducing ambients were explored; one was done under vacuum (slightly reducing) and the second was performe d in forming gas (very reducing). It is found that the vacuum anneal c aused a reduction in the remanent polarization and a concomitant decre ase in the isolated Fe3+ EPR resonance. The Fe3+-V(o) complex EPR sign al was relatively unaffected by this vacuum anneal. By injecting charg e using an ultraviolet (UV) light and an applied bias combination, the polarization and the isolated Fe3+ signal intensity were restored, th ereby suggesting that the suppression of the remanent polarization is due to trapping of electronic charge at the domain walls. For the form ing gas anneal, we observe a much larger decrease in remanent polariza tion with an accompanying decrease in both the isolated Fe3+ and Fe3+- V(o) complex EPR signals. For this anneal, charge injection by the UV light/bias combination did not restore the polarization nor the EPR de nsities. The remanent polarization, the isolated Fe3+, and the Fe3+-V( o) complex could be restored only by a reoxidizing anneal, suggesting that ionic defects (oxygen vacancies) are now responsible for pinning the domain walls. Collectively, these results suggest reducing anneals can suppress the amount of switchable polarization in BaTiO3 by eithe r electronic or ionic trapping mechanisms.