Kinetics and thermodynamics of intracrystalline Fe-Ga distribution in Y3(Fe,Ga)5O12 |
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Authors: | R Nitsche G Tippelt G Amthauer |
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Affiliation: | (1) Institut für Mineralogie, 5020 Salzburg, Austria;(2) Present address: Technische Hochschule Darmstadt, Fachbereich Materialwissenschaft, 64295 Darmstadt, Germany |
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Abstract: | Garnets of composition Y3Fe5–x
Ga
x
O12, withx=0–5, were synthesized from oxides. Samples with various Ga content were annealed at temperatures between 700–1290° C; the heating duration varied between 90 s and 1350 h. Cation distribution was measured by Mössbauer spectroscopy at room temperature. The standard free energy change for the exchange reaction Fe3+ (tet)+ Ga3+ (oct) Fe3+ (oct)+Ga3+ (tet) is about 20 kJ mol–1, and decreases slightly with increasing Fe content. The specific rate constants for the ordering process were determined according to the Mueller model for order-disorder kinetics. The activation energies for the ordering process between 200–250 kJ mol–1 were calculated from the temperature dependence of the specific rate constants. |
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