Lithium Insertion in La 2 NiO 4+y
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LITHIUM INSERTION IN La 2NiO4+Y
A. V~rez, U. Amador, E. Mor~n & M.A. Alario-Franco Dpto. Quimica Inorginica. Fac. C. Quimicas. Universidad Complutense, 28040 Madrid. SPAIN. ABSTRACT A series of lithium inserted La 2NiO4÷y has been prepared by the soft chemistry route with n-butyllithium at room temperature. The insertion leads to a lowering in symmetry, from the tetragonal K2NiF4 type to an orthorhombic structure. Neutron diffraction experiments show that as in stoichiomeantiferromagnetic. tric La 2NiO 4. the inserted material is Complex impedance measurements indicate it to be an ionic conductor in the temperature range extending from 60 to 300°C. INTRODUCTION Lithium insertion is one of the most interesting areas of research in Solid State Chemistry since, besides the instrinsic these new materials, of synthesis in the interest lithium-inserted materials are potentially useful in a number of In addition, etc [1]. displays, batteries, devices: perovskite-related materials are presently the subject of much work due to the upsurge in research in superconductivity after Bednorz and Muller's discovery [2]. After our lithium insertion work on the so called 1-2-3 and related materials, where extended defects [3], relatively fast Li-ionic conductivity [4] and novel phases have been found (5], we have performed some work in materials based on the K NiF _xM1x CuO44 structure type. Among them, (and besides the obvious La 2"2which, concerning Li-insertion, will be reported in due course) the La 2NiO 4+y constitutes an interesting example since, being it has rather different closely related in structural terms, transport and magnetic properties. When prepared in air, at 1570K, and slow cooling, y-0.17, the material is tetragonal, interstitial S.G.(space group) 14/mmm. At this stoichiometry, oxygen is present in the (1/4, 1/4, -1/4) positions, within a a and the material is tetrahedron of lanthanum ions [6), semiconducting diamagnet. However, the stoichiometric compound, when y=0, is orthorhombic, S.G. Bmab (standard Cmca), and becomes due to the ordering of a semiconducting antiferromagnetic, magnetic moments of the Ni(II) ions. We will show below that, upon insertion of lithium in the oxidized material, rather similar changes take place in both the nuclear and magnetic structures. EXPERIMENTAL La NiO 2
was prepared
by the standard ceramic method
4Ry Mat. Res. Soc. Symp. Proc. Vol. 210.©C1991 Materials Research Society
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La 20 3 and NiO as starting materials annealed in air at 1570K and slow cooling down to room temperature. Lithium insertion has been carried out by the "soft chemistry" route using a solution of n-butyllithium in hexane as described in reference [3]. Powder X-ray diffraction was performed on a Siemens D-500 diffractometer with CuKa radiation filtered by Ni, using silicon as the internal standard. Neutron powder diffraction measurements were made at 300K, 90K, 50K, 20K and 1.5K using the high resolution D2B Diffractometer at the Institute Laue-Langevin (Grenoble). Neutrons of wavelength 1.594 A
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