Plasma Electrolytic Synthesis and Characterization of Bismuth-Containing Oxide Films on Titanium

Bismuth-containing films on titanium were formed by single-stage plasma electrolytic oxidation (PEO) in the pulsed mode in an electrolyte with dispersed particles containing metallic bismuth. The surface morphology and composition of the prepared films were studied by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). The bismuth modification of Ti/TiO₂ films leads to the appearance of anodic photocurrents in the visible region of the spectrum, a shift in flat-band potentials to the cathodic region, and an increase in concentration of charge carriers. The pulse duration τ (0.02 or 0.05 s) noticeably affects the characteristics and properties of the prepared film composites. At τ = 0.02 s, agglomerates of particles 0.2 to 1 μm in diameter with an increased bismuth content are formed on the oxide film surface. Such film composites have a narrow bandgap of 1.62 eV and exhibit the highest photoelectrochemical activity under the visible light.