Structural Phase Transition and Magnetism in Ni Intercalated NbSe2

Abstract

In this article, we report the synthesis and structural characterization of polycrystalline NixNbSe2 (x = 0, 0.05, 0.1, 0.15, 0.2, 0.25) and single crystals of NixNbSe2 (x = 0.14, and 0.25). The intercalation limit of Ni in NbSe2 is found to be 25 mole%, above which NiSe remains as an impurity phase. Single crystal diffraction studies show two distinct phase transitions with Ni intercalation in NixNbSe2.The phase evolves from a mixture phase (2H+4H) for the pristine NbSe2 to Ni intercalated 2H phase for 0 ≤ x ≤ 0.2, which transforms to the 2H(I) phase with a 2𝑎𝑜 x 2𝑎𝑜 x 1𝑐𝑜 order superstructure for 0.20 ≤ x ≤ 0.25 in NixNbSe2 at the reaction temperature of 900 °C. The polytype remains intact during the phase formation, but the sub–polytype varies; i.e., the crystal symmetry and atom coordinates change. Intercalation of Ni induces more covalent character in the phases by interacting with the adjacent NbSe2 layers, which is evident from the XPS and theoretical study. Theoretical calculation on Ni0.25NbSe2 shows that the magnetic spins are very weakly spin-polarized, which is also reflected in the magnetic measurement study. Magnetic measurements on NixNbSe2 (x = 0.05, 0.1, 0.2, 0.25) show very weak magnetic properties for all the compounds.