Neutron Diffraction Study of La3Ni2O7: 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. Rerefinement 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.