Strain relaxation and spinodal decomposition in composition adjusted TiO₂-VO₂ films on TiO₂(100) substrates

In this study, we investigate the process of strain relaxation and spinodal decomposition in TiO₂-VO₂ films on TiO₂(100) substrates. Herein, the film composition was adjusted to Ti_0.2V_0.8O₂ for the relaxation of the in-plane tensile c-axis strain in the films. A 115 nm thick Ti_0.2V_0.8O₂ solid-solution film is epitaxially grown on a rutile-type TiO₂(100) substrate using a pulsed laser deposition technique, and is annealed inside the spinodal region. Reciprocal space mapping measurements show that the in-plane tensile c-axis strain is almost fully relaxed in the solid-solution film. Scanning transmission electron microscopy (STEM) observation results reveal that the annealed film causes spinodal decomposition along the c-axis direction, forming vertically aligned multilayer structures. The STEM observations also suggest the presence of interfacial misfit dislocations along the c-axis, indicating the generation of plastic strain relaxation along the c-axis in the film. Composition analysis reveals that the Ti-V interdiffusion between the film and substrate is considerably suppressed. The overall results of this study show that the composition adjustment to Ti_0.2V_0.8O₂ is effective for strain relaxation along the in-plane c-axis and occurrence of spinodal decomposition with reduced Ti-V interdiffusion in the TiO₂-VO₂ films on TiO₂(100). Our study helps establish a method for the formation of nanostructures via spinodal decomposition in the TiO₂-VO₂ films.