Phase diagram of La2NiO(4+delta) (0 less than or equal to delta less than or equal to 0.18). 1: Phases at room temperature and phase transition above delta equal to 0.15

La2NiO(4+delta) was prepared in the range of 0.00 less than or equal to delta less than or equal to 0.18. Oxygen stoichiometry, structure and phase transition were studied by TG-DTA (Thermogravimetric and Differential Thermal Analysis) and powder X-ray diffraction measurements. Five phases, orthorhombic Bmab (delta = 0.00), pseudo-tetragonal (delta = 0.02), orthorhombic (0.05 less than delta less than 0.09), tetragonal I4/mmm (0.1 less than delta less than 0.15) and orthorhombic Fmmm (delta greater than or equal to 0.15), appear in sequence of delta with intervals of coexistence range at room temperature. The orthorhombic phase (Fmmm) shows a first-order phase transition to a tetragonal phase (I4/mmm) with elevating transition temperatures from 320 K for delta = 0.15 to 430 K for delta = 0.18. A tentative phase diagram of La2NiO(4+delta) is also shown.