Fig. 1: Structural and optical changes upon phase transition in Ti3O5 nanocrystals at thermal equilibrium.
a, b Atomic structure of the β- and λ- phases, respectively, with the calculated charge density for the two bands centered at 1.1 eV (yellow) and 0.3 eV (cyan) below the Fermi level, strongly localized around Ti2-Ti2 and Ti3-Ti3 dimers; ϕβ and ϕλ are the monoclinic angles of respectively β- and λ- unit cell. c, d Calculated density of state projected on Ti1 (dotted lines), Ti2 (dashed lines), and Ti3 (solid lines) in the β- and λ- phases, respectively. The black arrow is the energy transfer corresponding to the 1.55 eV pump photons. e, f Mean calculated optical conductivity (σ) for β- and λ- phases, respectively (black line). Yellow (cyan) curve is the contribution from the band at −1.1 eV (−0.3 eV). Diagonal contributions to the conductivity are shown in Fig. S1. g, h X-ray powder diffraction data on Ti3O5 nanocrystals: g change in c-parameter of the monoclinic unit cell with a jump showing the first order phase transition at TSM = 460 K between the β- and λ-phases; h Temperature dependence of the monoclinic angle ϕ with the first order phase transition at TSM = 460 K (between the β- and λ-phases which co-exist in these nanocrystals below TSM), and a continuous locking at 90° characterizing the symmetry change towards the Cmcm high temperature α-phase. The critical temperature Tc = 500 K for this second order phase transition is shown with a dotted vertical line.
