Kinetic demixing of a solid solution oxide should occur during deformation if the cations have different mobilities and if the rate of stress-directed diffusion is not limited by oxygen diffusion. A theoretical treatment of kinetic demixing in mixed oxides due to a nonhydrostatic stress has been developed. Both the magnitude of the steady-state composition difference and the time constant which characterizes the transient behavior have been determined. Kinetic decomposition of a stoichiometric, ternary oxide can occur when the transport rates of the constituent oxides are different, provided that the magnitude of the driving force exceeds a certain limit. The critical differential stress for kinetic decomposition is a function of the free energy of formation of the compound and the transport coefficients of the species. The growth rate of the constituent oxide phase has also been evaluated.
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Acknowledgemenfs-Theauthorsare deeply indebted to ProfessoHrermannSchmalzriefodr introducingthemtothe (75) topicof kineticdemixinganddecompositionandfor numer-ous stimulatingdiscussionson the subject.Discussionswith G. Brian StephensonandMervyn S. Patersonwerealsovery helpful. Support from the National Science Foundation through Grants. No. DMR-8100131,DMR-8500480.and INT-8504802is gratefullyrecognized.
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