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A phenomenological treatment of cation distribution in spinels: System (Ni(1-x)Alx)(t)[NixAl2-x](0) O-4

Iyengar, GNK and Balasubramanya, R and Jacob, KT (1997) A phenomenological treatment of cation distribution in spinels: System (Ni(1-x)Alx)(t)[NixAl2-x](0) O-4. In: High Temperature Materials And Processes, 16 (1). pp. 39-48.

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Presented in this paper is a phenomenological model for cation distribution between crystallographically non-equivalent sites of the spinel structure at high temperature. Interactions between ions on each site are characterized by enthalpy parameters. A regular solution model is assumed for mixing of the species on tetrahedral and octahedral sites, independent of the nature of bonding in the solid. The model provides an equation which is functionally similar to that proposed by O'Neill and Navrotsky /15/ based on electrostatic considerations. However, the phenomenological model gives a more realistic interpretation of the constants involved in the equation. Recent experimental data on temperature dependence of cation distribution in NiAl2O4 are used to test the validity of the different models. Since Ni2+ ion in tetrahedral coordination exhibits Jahn-Teller distortion, an entropy corresponding to randomization of the distortion in the cubic phase has been incorporated in the model. Inclusion of the Jahn-Teller entropy in the expression for the cation distribution appears to be as important as introduction of quadratic dependence of enthalpy of disordering (Delta H-D) on cation distribution. Best statistical fit to experimental data is obtained when both Jahn-Teller entropy and energetics of interaction of ions are incorporated in the model.

Item Type: Journal Article
Publication: High Temperature Materials And Processes
Publisher: Freund Publishing House
Additional Information: Copyright of this article belongs to Freund Publishing House
Department/Centre: Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited: 11 Feb 2010 07:04
Last Modified: 11 Feb 2010 07:04
URI: http://eprints.iisc.ac.in/id/eprint/18400

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