R. Nitsche et al., KINETICS AND THERMODYNAMICS OF INTRACRYSTALLINE FE-GA DISTRIBUTION INY3(FE, GA)5O12, Journal of Materials Science, 29(11), 1994, pp. 2903-2910
Garnets of composition Y3Fe5-xGaxO12, with x = 0-5, were synthesized f
rom oxides. Samples with various Ga content were annealed at temperatu
res between 700-1290-degrees-C; the heating duration varied between 90
s and 1350 h. Cation distribution was measured by Mossbauer spectrosc
opy at room temperature. The standard free energy change for the excha
nge reaction Fe3+ (tet) + Ga3+ (oct) <-> Fe3+ (oct) +Ga3+ (tet) is abo
ut 20 kJ mol-1, and decreases slightly with increasing Fe content. The
specific rate constants for the ordering process were determined acco
rding to the Mueller model for order-disorder kinetics. The activation
energies for the ordering process between 200-250 kJ mol-1 were calcu
lated from the temperature dependence of the specific rate constants.