Stoichiometry, structure, and properties of La(2-x)Sr(x)NiO(4 +- delta) and La2NiO(4 + delta)

摘要

The oxygen content phase diagram of La(sub 2)NiO(sub 4+(delta)) has been studied in detail using x-ray and neutron diffraction data from well-characterized specimens. There are numerous phase separations and phase transitions which are observed with changes in temperature and composition. The complexity of the phase diagram arises primarily from oxygen defect interactions, however the authors have also obtained evidence for coupled charge and spin ordering at (delta) = 0.125 corresponding to organization of holes into ordered domain walls. These domain walls act as antiphase boundaries between stripes of antiferromagnetically ordered nickel moments. Neutron scattering data on Sr-substituted compositions with well-defined oxygen content indicate incommensurate charge and spin correlations closely related to those in the x=0, (delta) = 0.125 composition. The incommensurability approaches 1/4 and the correlation length increases as the hole concentration approaches p = x+2(delta) = 0.25.