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Dielectric loss caused by oxygen vacancies in titania ceramics

✍ Scribed by Robert C. Pullar; Stuart J. Penn; Xiaoru Wang; Ian M. Reaney; Neil McN. Alford

Publisher
Elsevier Science
Year
2009
Tongue
English
Weight
533 KB
Volume
29
Category
Article
ISSN
0955-2219

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✦ Synopsis

Undoped TiO 2 exhibited deterioration in microwave (MW) dielectric loss as it reached its maximum density due to the reduction of Ti 4+ to Ti 3+ causing oxygen vacancies at high sintering temperatures. By adding small amounts of acceptor dopants with ionic radii between 0.5 and 0.95 Å, reduction during sintering was suppressed. The upper limit of ionic radius was discrete with almost no observed effect using dopants >0.96 Å ionic radius. In addition, the microwave dielectric loss of undoped TiO 2 could be improved by annealing at 1500 • C for 10 h in air, presumably as a result of re-oxidation. High loss samples exhibited a dark 'core' to the naked eye which was absent in low loss ceramics. Transmission electron microscopy revealed that grains in the dark core contained planar defects attributed to the condensation of O vacancies onto specific crystallographic planes, in a manner similar to that observed in Magnelli phases.

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