Ultrafast dynamics of a photoinduced phase transition in single-crystal trititanium pentoxide

We investigate photoinduced phase transition of $Ti 3 O 5$ using the pump-probe method in an ultrafast electron microscope. We measured time-resolved electron diffraction patterns of single-crystal lamellae of $Ti 3 O 5$ excited by the femtosecond laser at the wavelength of 800 and 400 nm. Under 800 nm laser excitation, the photoinduced phase transition from the β-phase to the λ-phase with a similar timescale to previous measurements conducted using nanocrystals was observed. This indicates that the photoinduced phase transition is not a phenomenon influenced by the material surface, size, or boundary, but an intrinsic property in a bulk crystal of $Ti 3 O 5$⁠. The photoinduced phase transition was not detected, when excited by the laser at the wavelength of 400 nm. The results are discussed based on the electronic states of β- $Ti 3 O 5$ and λ- $Ti 3 O 5$⁠. The density of the dissociated interatomic bonds between Ti at the specific site should be an important factor for triggering the photoinduced phase transition.