Non-metallic electrical transport properties of a metastable λ-Ti3O5 thin film epitaxially stabilized on a pseudobrookite seed layer

A metastable phase of Ti3O5, λ-Ti3O5, has been studied as a promising optoelectronic material applicable to optical memories and switching devices because it undergoes structural phase transitions, accompanied by changes in optical and electrical properties, under a variety of external stimuli such as heat, visible light, pressure, and electrical current. Theoretical calculations and optical and magnetic measurements have suggested that λ-Ti3O5 is a metal. However, its electrical transport properties have not been directly measured to date because λ-Ti3O5 has so far been synthesized only as nanocrystals or aggregates thereof. In this study, we synthesized (100)-oriented λ-Ti3O5 epitaxial thin films on perovskite LaAlO3 (110) substrates by pulsed laser deposition. Precise control of oxygen supply during the growth and introduction of a MgTi2O5 seed layer with a pseudobrookite structure enabled epitaxial growth of λ-Ti3O5. These λ-Ti3O5 epitaxial thin films showed a lower electrical resistivity ρ (∼7.9 × 10−2 Ω cm) than bulk single crystals of β-Ti3O5 (high resistance phase) at 300 K. On the other hand, the ρ value of the λ-Ti3O5 thin films exhibited a semiconducting temperature dependence with negative dρ/dT.