Thermogravimetric investigation of the relation between oxygen stoichiometry, temperature and oxygen partial pressure in Nd1−xCaxMnO3+δ perovskites (x≈0.5) Original Research Article

The temperature and O2 partial pressure dependence of the oxygen stoichiometry (3+δ) in Nd0.52Ca0.48MnO3+δ 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 ΔH0=278 kJ/mol, ΔS0=119 J/mol K as typical values for the formation of oxygen vacancies. In the oxygen-excess regime δ is related to the formation of cation vacancies, and only an empirical relation between temperature and pO2 for δ=0 can be given. The defect-chemical data set can be used as a tool to prepare Nd1−xCaxMnO3+δ perovskites with well-defined oxygen stoichiometry.