Advisory Committee Chair
Mary Ellen Zvanut
Advisory Committee Members
Gregg M Janowski
Andrei Stanishevsky
Document Type
Thesis
Date of Award
2008
Degree Name by School
Master of Science (MS) College of Arts and Sciences
Abstract
In this investigation we studied the thermal stability of defects in as-received (100) strontium titanate substrate during isochronal and isothermal anneals in vacuum and oxygen ambients. Using electron paramagnetic resonance spectroscopy, our purpose was to correlate the responses of the Fe+3Vo associate defect to either oxygen movement in substrates or to changes in the charge states of the Fe+3Vo defect. Isochronal vacuum anneals at T < 600 0C show increases in the relative EPR intensity of Fe+3Vo, implying increases in oxygen vacancies, but the decreases at T > 600 0C are not as yet clear. Isochronal oxygen anneals were conducted to compare/contrast responses of Fe+3Vo to thermal treatments in different ambients. Vacuum and oxygen anneals produced surprisingly similar results, suggesting that similar effects were occurring even though the ambients were different. Also, the isothermal anneals at 400 and 700 0C indicate that the order magnitude of the decay time of Fe3+Vo is the same in vacuum and oxygen ambients. The vacuum and oxygen anneal data was reviewed more thoroughly and two clear distinctions can be made. Analysis of Fe3+Vo/Fe3+ ratio showed that although the value of this ratio remained constant for the oxygen anneals, it consistently increased during the vacuum anneals. The sequential anneals demonstrated that the effects of oxygen anneal can be reversed by a subsequent vacuum anneal. However the vacuum-vacuum sequential iii anneals showed that a second treatment in vacuum does not always reverse the effect of the first heat treatment, thus confirming that the oxygen and vacuum ambients do cause different physical changes. Although the basic mechanisms for defect changes during annealing are not clear, our work does provide practical information about the stability of point defects during annealing. Since substrates from commercial vendors were used our results can be applied directly to film deposition conditions. Using a range of temperatures, we have shown that the Fe3+Vo defect is stable at temperatures less than 500 0C during thermal treatments in vacuum and oxygen ambients.
Recommended Citation
Jeddy, Shehnaz, "Thermal Stability Of Defects In Strontium Titante Substrates For Multiferroic Materials" (2008). All ETDs from UAB. 3591.
https://digitalcommons.library.uab.edu/etd-collection/3591