Properties of thermally treated Ti/TiO₂ nanotubes: increased crystalline phase and carrier concentration

Chem. Met. Alloys 16 (2023) 37-42

Olesia SHMYCHKOVA, Tatiana LUK’YANENKO, Alexander VELICHENKO

https://doi.org/10.30970/cma16.0432

As prepared Ti/TiO₂ materials exhibit a notable presence of X-ray amorphous compounds on the surface, likely corresponding to hydrated titanium oxides. The primary crystalline phase observed is titanium dioxide in the anatase form. Traces of metallic titanium are also found on the surface. There is an increase in the proportion of the crystalline phase, with a significant rise in the content of metallic titanium, accounting for approximately one-third of the composition upon thermal treatment at 500°C for 3 hours in an air atmosphere. Through partial electrochemical reduction of nanotubes, it is possible to obtain titanium suboxides with improved electrical conductivity. Subsequent cathodic reduction of nanotubes for one hour results in the uniform deposition of a galvanic coating composed of metallic platinum on the material’s surface. The thermally treated Ti/TiO₂ nanotubes exhibit n-type semiconductor behavior, with a flat-band potential of -0.589 V and a carrier concentration of 6×10²⁰ cm^-3. During thermal treatment, the flat-band potential and carrier concentration increase, possibly due to the more crystalline structure of the material. This structural change is accompanied by an increase in the proportion of metallic titanium, which acts as an electron donor. A similar phenomenon is observed when a discontinuous platinum coating is applied to the surface of reduced nanotubes. In this case, heat treatment causes platinum migration into the bulk of the composite, which, when dispersed within the oxide, further increases the number of carriers.

Semi-logarithmic quasi steady-state polarization curves for reduced Ti/TiO₂-Pt nanotubes.

Keywords

Carrier concentration / Thermal treatment / Phase composition / Nanotubes