Study of Mg ion Intercalation in Polycrystalline MoO3 Thin Films

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Abstract
As-deposited amorphous MoO3 films were found to crystallize into a stable orthorhombic phase on annealing in air at 350°C. The feasibility of using Mg ions as intercalants, in polycrystalline MoO3 thin films has been investigated. These ions were intercalated galvanostatically at a constant current density of 166 µA/cm2. Structural studies carried out on intercalated films, show lattice expansion along b axis by 2.35% for x = 0.1 and 3.17% for x = 0.3. Partial restoration of b-axis is observed on deintecalation. The chemical status of Mo and O ions, before and after intercalation has been investigated using Photoemission Spectroscopy (core level spectra). Core level (CL) of Mo 3d levels indicate the presence of Mo+6 oxidation state only in unintercalated films, with a stoichiometry of MoO3. The intercalated ions are found to reduce Mo ions as revealed by the presence of Mo+5, Mo+4 and Mo+3 states in addition to Mo+6 state. Formation of Mg–O bonds is seen from the CL spectrum of O1s levels. From cyclic voltammetry experiments the estimated diffusion coefficient of Mg ions is found to be of the order of 10-19 cm2/s and the films are stable even after 300 cycles.