Structure and transport properties of titanium oxide (Ti2O, TiO1+δ, and Ti3O5) thin films

Abstract Titanium oxides have partially filled or empty d orbital and are stable at various oxidation states with different structures and unique properties. Here, three kinds of titanium oxide thin films of hexagonal Ti 2 O metal, cubic TiO 1+ δ superconductor, and monoclinic γ-Ti 3 O 5 semiconductor, were successfully grown on α-Al 2 O 3 substrates by a pulsed laser deposition technique, through ablating a pure titanium target under different oxygen pressures. The electrical resistivities of these films increase with increasing oxygen content. The metallic behaviors of Ti bulk and Ti 2 O film can be described by the Bloch–Gruneisen formula, and the semiconducting behaviors of TiO 1 +δ films in normal state and γ-Ti 3 O 5 film obey the variable range hopping and the small polaron hopping conduction mechanisms, respectively. For titanium monoxide TiO 1+ δ (1.05 ≤ 1+ δ  ≤ 1.17) films, increasing oxygen content is accompanied by an increase of disorder, a decrease of electron density of states at the Fermi level, and an enhancement of carrier localization, leading to a suppression of superconductivity.