Phase Transformations of Individual Ti 3 O 5 Nanocrystals Studied by In Situ Electron Microscopy

Phase changes in individual sub-micron crystals of Ti$_3$O$_5$ are studied by in-situ transmission electron microscopy. An irreversible transition from the stable beta- to the metastable lambda-phase is induced by slow temperature changes in thermal equilibrium or by nanosecond laser pulses. The expansion of the crystals during the phase transformation is measured in real space by imaging and in reciprocal space by electron diffraction. An incomplete or suppressed phase transformation under slow heating indicates that the kinetic barrier for the thermal transformations from the beta- to the lambda-phase and to the high-temperature alpha-phase is higher than in bulk material. On the other hand, a single nanosecond laser pulse at 1064 nm is found to induce a complete transformation from the beta- to the lambda-phase in sub-micron-size crystals of Ti$_3$O$_5$. As in previous studies, laser pulses at longer wavelengths (1064 nm) are found to be more appropriate than at shorter wavelength (532 nm) where inter-band transitions and the rupture of bonds occur. Here, the laser pulses lead to a purely thermal switching from the beta- to the lambda-phase.