Abstract: A series of La_(2-x)Sr_xNiO_4(0.0≤x≤1.0) oxides with the tetragonal K_2NiF_4 structure were prepared. The cell parameters were measured by powder X-ray diffraction (XRD) technique; the reducibility was determined by temperature programmed reduction(TPR). Results show that the changing orders of the highest reducing peak temperature with composition(x) contrast to that of cell parameter a, but agree with that of c. The reducing mechanism for La_(1.7)Sr_(0.3)NiO_4 was investigated by TPR and XRD technique. We found that the first two reducing peaks in TPR profile correspond mainly to the reducing process from Ni~(3+) ion to Ni~(2+). This point was also identified by the calculation of axial ratio indirectly; therefore the highest reducing peak is the structural destroying peak.

Key words: La_2-xSr_xNiO₄, La_1.7Sr_0.3NiO₄, XRD technique, TPR