Influence of non-stoichiometry on the structural and electronic metal-insulator transition in 18O isotope-doped vanadium oxide films

Abstract

The synthesis of vanadium oxide compounds, V₂¹⁸O_3-x, with oxygen non-stoichiometry and heavy oxygen isotope doping (¹⁸O), was achieved via the cathode arc sputtering method. The microstructural characteristics and stoichiometric properties of the resulting nanocrystalline films were examined using X-ray diffraction, atomic force microscopy and Rutherford backscatter spectrometry. The concentration of defects leading to the suppression of the structural and electronic metal-insulator transition was evaluated through Raman spectroscopy and the analysis of electrophysical properties. A semi-empirical simulation of the lattice dynamics of vanadium oxide was also performed. Notable temperature anomalies in resistance, impedance, and relaxation time were observed. A model involving the deformation of octahedra and the splitting of oxygen vacancies multiplets was proposed to explain the formation of impurity subbands. Furthermore, a change in the sign of magnetoresistance and magnetoimpedance at specific temperatures, along with the effect of photoconductivity, was discovered.