Studies on oxygen dissociation pressure of LnMnO3 (Ln = rare earth) with the e.m.f. technique

Abstract

The oxygen dissociation pressure of LnMnO3 (Ln  La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y or Sc) was measured at high temperature (1170–1400 K) by means of e.m.f. using stabilized ZrO2 as a solid electrolyte. Assuming that the decomposition reaction proceeds in a stoichiometric form, a standard Gibbs free energy change of decomposition was determined from the oxygen dissociation pressure. The variation of the free energy change with change in identity of Ln was investigated. It was found that the energy change depends strongly upon both the crystal structure and the ionic radius of Ln3+. The standard Gibbs free energy change of formation for LnMnO3 compounds was obtained from the standard Gibbs free energy change for the decomposition reactions and those for the formation of the decomposition materials.