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 Ruddlesde n-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 symmetr y lowering at low temperature, such as occurs for n = 1; however, no eviden ce for this is found in low-temperature neutron data. Re-refinement of the n = 3 phase reveals significant strain within the perovskite-type layers th at appears to increase with n, This strain is used to explain the absence o f low temperature phase transformations for n > 1, In the absence of a phas e transformation, possible origins for the resistivity and susceptibility a nomalies are considered, (C) 2000 Academic Press.