Thermodynamic properties of complex oxides in the La-Ni-O system

Complex oxides La₂NiO_4+δ, La₃Ni₂O_7−δ, La₄Ni₃O_10−δ and LaNiO_3−δ, the members of Ruddlesden-Popper series La_n+1Ni_nO_3n+1, were prepared using citrate precursors. The stability range of LaNiO_3−δ in air as well as the oxygen nonstoichiometry of La₃Ni₂O_7−δ and La₄Ni₃O_10−δ as a function of temperature and oxygen partial pressure was determined by means of thermogravimetric technique. Decomposition temperatures of La₃Ni₂O_7−δ, La₄Ni₃O_10−δ and LaNiO_3−δ in air were determined by conductivity measurement method. The boundary of stability for La₄Ni₃O_10−δ was determined by EMF measurements of galvanic cell with oxygen conducting solid electrolyte. The isothermal (1400 K) projection of La-Ni-O system phase diagram to the plane “log(PO₂)-relative mole fraction of metal components” was suggested.