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Kinetics of Cation Redisribution in Ferrospinels
Author(s) -
Sujata K.,
Mason Thomas O.
Publication year - 1992
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1992.tb07842.x
Subject(s) - nucleation , kinetics , homogeneous , activation energy , chemistry , electrical resistivity and conductivity , ionic bonding , redistribution (election) , kinetic energy , analytical chemistry (journal) , relaxation (psychology) , materials science , ion , thermodynamics , engineering , social psychology , psychology , physics , organic chemistry , chromatography , quantum mechanics , politics , political science , law , electrical engineering
In situ electrical resistivity measurements were employed to follow the kinetics of cation redistribution in ferrospinels, x Fe 3 O 4 –(1 – x )MeFe 2 O 4 (Me = Co, Mg, Mn, or Ni) or x Fe 3 O 4 –FeMe 2 O 4 (Me = Al) with x ≥ 0.2. Relaxation temperatures (at 20°C/min heating rate) were established and kinetic parameters—activation energies and time constants—were determined for each cation. These parameters were insensitive to grain size, cation ratio, and oxygen nonstoichiometry. The mechanism was shown to be a local “homogeneous” point defect reaction in contrast to the “heterogeneous” nucleation and growth mechanism reported to take place in ferrispinels lacking Fe 2+ . Electron hopping between Fe 2+ and Fe 3+ in ferrospinels apparently screens the excess ionic charge associated with the diffusing species and enables homogeneous point defect reactions with lower attendant activation energies to take place.