Phase equilibria and crystal structures of phases in the La-Fe-Ni-O system at 1370 K in air

The phase equilibria in the La-Fe-Ni-O system have been studied at 1370 K in air, and the La-Fe-Ni-O phase diagram at constant temperature and pressure has been constructed. Based on x-ray diffraction results for samples prepared by standard solid-state reactions and via citrate and nitrate routes, the following solid solutions have been shown to exist at 1370 K in air: LaFe1 - xNixO3 - delta (0 < x <= 0.4, sp. gr. Pbnm; 0.6 <= x <= 0.8, sp. gr. R<(3)over bar> c), La-4(Ni1 - yFey)(3)O10 - delta (0 < y <= 0.3), La-3(Ni1 - zFez)(2)O7 - delta (0 < z <= 0.05), La2Ni1 - vFevO4 + delta (0 < v <= 0.05), NikFe3 - kO4 (0.81 <= k <= 1.05), Ni1 - mFemO (0 < m <= 0.05), and Fe2 - p NipO3 (0 < p <= 0.04). The lattice constants and structural parameters of single-phase samples have been refined by the Rietveld profile analysis method.