OXYGEN NONSTOICHIOMETRY AND CRYSTAL AND DEFECT STRUCTURE OF PRMNO3+Y AND NDMNO3+Y

Praseodymium and neodymium manganates LnMnO(3+y) have been prepared an d characterized by powder X-ray and neutron diffraction together with thermogravimetric and chemical titration analysis. Both ternary oxides have an orthorhombically distorted perovskite-like structure (Pbnm sp ace group) with unit cell parameters a = 5.4562(7), b = 5.5914(7), c = 7.672(1)Angstrom and a = 5.4116(9), b = 5.6928(9), c = 7.599(1) Angst rom for praseodymium and neodymium manganates, respectively. A small d eficiency in manganese has been found together with an oxygen excess, which can likely be described by the cation disorder: Pr0.95Mn0.94O3 a nd Nd0.97Mn0.95O3. The thermodynamics of the oxygen exchange process h ave been described in terms of partial molar enthalpy and partial mola r entropy of the oxygen dissolution in the lattice. (C) 1995 Academic Press, Inc.