Phase Equilibria and Crystal Structures of Phases in the La-Fe-Ni-O System at 1370 K in Air

摘要

The phase equilibria in the La-Fe-Ni-O system have been studied at 1370 K in air, and the La-Fe-Ni-0 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: LaFe_(1-x)Ni_xO_(3-δ) (0 < x ≤ 0.4, sp. gr. Pbnm; 0.6 ≤ x ≤ 0.8, sp. gr. R3 c), La_4(Ni_(1-y)Fe_y)_3O_(10-δ) (0 < y ≤ 0.3), La_3(Ni_(1-z)Fe_z)_2O_(7-δ) (0 < z ≤ 0.05), La_2Ni_(1-v)Fe_vO_(4+δ) (0 < v ≤ 0.05), Ni_kFe_(3-k)O_4 (0.81 ≤ k ≤ 1.05), Ni_(1-m)Fe_mO (0 < m ≤ 0.05), and Fe_(2-p)Ni_pO_3 (0 < p ≤ 0.04). The lattice constants and structural parameters of single-phase samples have been refined by the Rietveld profile analysis method.