Crystal structures and electronic configuration of the low valent layered nickelates are quite similar to those in high temperature superconducting cuprates.  In particular, Ni1+/Ni2+ nickelates as well as Cu2+/Cu3+ cuprates possess the same electronic state of transition metal (3d9/3d8) in a square planar coordination.  Therefore, the nickelates have a potential to exhibit properties similar to the cuprates. Ln4Ni3O8, Ln = La and Nd have been prepared in a pure form allowing a detailed investigation of their magnetic and electronic properties.  The La4Ni3O8 phase exhibits spin fluctuation and a magnetic transition at 105 K.  Our recent X-ray and neutron diffraction data suggest that the magnetic transition originates from the Yahn Teller effect.  Even at low temperatures the La4Ni3O8 phase shows evidences of Ni atoms being in a high spin state that makes it different in comparison to the cuprates.  However, the spin state of Ni changes under high pressure.  Crystal structure and resistivity of La4Ni3O8 and Nd4Ni3O8 have been measured up to ~100GPa.  It was found that both phases exhibit structural phase transition in which fluorite Ln/O2/Ln block transforming to rock salt structural block leaving the infinite NiO2 layers intact.  Thus, at high pressure the structural motive, electronic configuration and the spin state of Ni1+/Ni2+ nickelates are identical to those in the superconducting cuprates.  The resistivity of Ln4Ni3O8 drops as pressure increases.  The nature of the pressure induced metal-insulator transition will be discussed.

Synthesis, structure, and electronic properties of low valent layered nickelates: La4Ni3O8 and Nd4Ni3O8

246th National Meeting (2013)

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