Phase stabilities of LnMn(2)O(5) (Ln=rare earth)

Decomposition temperatures of LnMn(2)O(5) (Ln = Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Y) were measured by thermogravimetry (TG) and differential thermal analysis under various oxygen partial pressures P-o2 = 10(-4)-1 atm. The decomposition reactions were confirmed by identifying the decomposition products with powder X-ray diffractometry and determining weight loss from TG as follows. LnMn(2)O(5) --> LnMnO(3) + 1/3Mn(3)O(4) + 1/3O(2) Among LnMn(2)O(5) phases the most stable phases are GdMn2O5 and DyMn2O5, while the most unstable phase is PrMn2O5. The Gibbs free energy, enthalpy and entropy changes of the decomposition reactions for LnMn(2)O(5) phase were determined from the oxygen partial pressure at the decomposition temperature. The standard enthalpies and entropies of formation of LnMn(2)O(5) were estimated