Spectroscopic and magnetic properties of the MNi(AsO4) (M = Li, Na) arsenates and crystal structure refinement of LiNi(AsO4)

摘要

Two compounds of general formula M Ni(AsO4) (M = Li, Na) have been synthesized and characterized by spectroscopic and magnetic techniques, The crystal structure of the LiNi(AsO4) phase was refined using X-ray powder diffraction data. The compound crystallizes in the orthorhombic system, space group Pnma, 10.284(2)Angstrom, b=5.909(1)Angstrom and c =4.853(1) Angstrom. The lithium compound adopts the olivine structure, whereas the sodium phase exhibits a layered structure. Diffuse reflectance spectra for both compounds show bands belonging to Ni(II) ions in an octahedral environment. Magnetic susceptibility measurements indicate antiferromagnetic interactions for both the lithium and sodium compounds. The magnetic behavior of LiNi(AsO4) is consistent with a 3D antiferromagnetic system, with an exchange parameter J/k =-9.9 Ii and a g-value of 2.19, The NaNi(AsO4) phase exhibits 2D antiferromagnetic behavior, which was analyzed by using a honeycomb model. The J/k value obtained is -7.0 ii, with g = 2.20, (C) 1998 Academic Press. [References: 25]