Neutron diffraction study of La2Ni2O7:: Structural relationships among n=1, 2, and 3 phases Lan+1NinO3n+1

Structural relationships among the n = 1, 2, and 3 members of the Ruddlesden-Popper series Lan+1NinO3n+1 are used to predict a lowering of symmetry in the n = 2 phase, subsequently observed and refined against neutron powder diffraction data. Resistivity and magnetic susceptibility measurements are presented for n = 2 and 3 that suggest the possibility of a further symmetry lowering at low temperature, such as occurs for n = 1; however, no evidence for this is found in low-temperature neutron data. Re-refinement of the n = 3 phase reveals significant strain within the perovskite-type layers that appears to increase with n, This strain is used to explain the absence of low temperature phase transformations for n > 1, In the absence of a phase transformation, possible origins for the resistivity and susceptibility anomalies are considered, (C) 2000 Academic Press.