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oxides; magnetic materials; thermogravimetric analysis (TGA); defects; thermodynamic properties
Abstract:
The temperature and O-2 partial pressure dependence of the
oxygen stoichiometry (3+delta) in Nd0.52Ca0.48MnO3+delta has
been investigated by means of thermogravimetry (TG). The data
have been successfully interpreted in terms of a defect-
chemical model distinguishing between regimes of oxygen
deficiency and oxygen excess. In the regime of oxygen
deficiency we find DeltaH(0)=278 kJ/mol, DeltaS(0)=119 J/mol K
as typical values for the formation of oxygen vacancies. In the
oxygen-excess regime delta is related to the formation of
cation vacancies, and only an empirical relation between
temperature and pO(2) for delta=0 can be given. The defect-
chemical data set can be used as a tool to prepare Nd1-
xCaMnO3+delta perovskites with well-defined oxygen
stoichiometry. (C) 2003 Published by Elsevier Science Ltd.
