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

Complex oxides La2NiO4+δ, La3Ni2O7−δ, La4Ni3O10−δ and LaNiO3−δ, the members of Ruddlesden–Popper series Lan+1NinO3n+1, were prepared using citrate precursors. The stability range of LaNiO3−δ in air as well as the oxygen nonstoichiometry of La3Ni2O7−δ and La4Ni3O10−δ as a function of temperature and oxygen partial pressure was determined by means of thermogravimetric technique. Decomposition temperatures of La3Ni2O7−δ, La4Ni3O10−δ and LaNiO3−δ in air were determined by conductivity measurement method. The boundary of stability for La4Ni3O10−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.