Decomposition oxygen partial pressures of Ln(1-x)Sr(x)MnO(3) (Ln=La, Nd and Dy)

The decomposition reactions of strontium doped rare earth manganites Ln(1-x)Sr(x)MnO(3) (Ln=La, Nd and Dy) in reducing atmospheres were studied at 1273 K. In the system for Ln=La, La1-xSrxMnO3 for 0.2 less than or equal to x less than or equal to 10.5 decomposed to MnO and (La1-xSrx)(2)MnO4, while the compounds for 0.5<x less than or equal to 1 decomposed to MnO and the oxygen deficient (La1-xSrx)(2)MnO4-delta phase in which the oxidation number of Mn is 3+ only and the oxygen defect delta is x-0.5. The decomposition oxygen pressures of Ln(1-x)Sr(x)MnO(3) were determined in the temperature range 1100 to 1400 K by the e.m.f. measurements using stabilized-zirconia solid electrolytes. The decomposition oxygen pressures of (Ln(1-x)Sr(x))(2)MnO4-delta and those in equilibrium with (Ln(1-x)Sr(x))(2)MnO4 and (Ln(1-x)Sr(x))(2)MnO4-delta were also determined. For all the compounds, their oxygen partial pressures linearly decreased with a decrease of the ionic radii of Ln(3+). The standard Gibbs energy changes of decomposition of the compounds were calculated from their oxygen partial pressures. (C) 1997 Elsevier Science S.A.