A conventional and high-resolution synchrotron X-ray diffraction study of phase separations in Pr2NiO4+δ

Several Pr₂NiO_4+δ samples with varying oxygen content have been examined by conventional and high-resolution synchrotron X-ray powder diffraction techniques. Three different phase separation regions have been identified with synchrotron diffraction, and the room temperature lattice parameters of each phase are reported, as well as conventional X-ray powder diffraction data on four single-phase regions of the phase diagram. The low temperature behavior of a sample with an average excess oxygen content of 0.020 was also studied, revealing phase coexistence and a tetragonal to orthorhombic phase transition on heating at 118 K. A semiquantitative oxygen concentration phase diagram is proposed on the basis of the amount of excess oxygen in the individual phases, as estimated from iodometric titrations and relative phase volumes. In addition, the overall stability field of Pr₂NiO_4+δ, showing the oxygen fugacity at the reduction and oxidation boundaries as a function of temperature, is reported.