The phase transition between gamma-trititanium-pentoxide (γ-Ti3O5) and delta-trititanium-pentoxide (δ-Ti3O5) was clarified from both experimental and theoretical viewpoints. With decreasing temperature, the monoclinic I2/c crystal structure of γ-Ti3O5 was found to switch to a monoclinic P2/a crystal structure of δ-Ti3O5 due to lowering of symmetry. Electrical conductivity (σ) measurement shows that γ-Ti3O5 behaves like a metallic conductor with a σ value of 4.7 S cm-1 at 320 K, while δ-Ti3O5 shows a semiconductive property with a σ value of 2.5 × 10-5 S cm-1 at 70 K. Optical measurement also supports that γ-Ti3O5 is a metallic conductor, while δ-Ti3O5 is a semiconductor with a band gap of 0.07 eV. First-principles calculations show that γ-Ti3O5 is a metallic conductor, and the energy state on the Fermi energy is composed of the 3d orbital of Ti and 2p orbital of O with one-dimensional linkage along the crystallographic c-axis. On the contrary, δ-Ti3O5 has a band gap, and the energy state around the Fermi energy is split into the valence band and the conduction band, which are assigned to the lower and upper Hubbard bands, respectively. Thus, the phase transition between γ-Ti3O5 and δ-Ti3O5 is caused by breaking of a one-dimensionally conducting pathway due to a Mott-Hubbard metal-insulator phase transition.
ASJC Scopus subject areas
- 化学 (全般)