Speaker
Description
Titanium oxide Ti$_3$O$_5$ is a remarkable transition-metal oxide that exists in a few crystal phases and can be switched reversibly between them by temperature, pressure or light excitation[1]. The transition between its $\beta$ and $\lambda$ phases is first-order and is accompanied by a change in its electronic and optical properties, which makes the material a good candidate for optical switching and storage, heat-storage ceramics and solar steam generation[2]. Understanding how fast such a transition can be driven, and what limits its reversal, is therefore essential for any use of this material. [3,4]
Ultrafast transmission electron microscopy (UTEM) makes it possible to follow these processes directly. A laser pump excites a nanometre-thin Ti$_3$O$_5$ lamella, and a time-delayed electron pulse records the diffraction pattern, from which the structural response is followed from nanoseconds up to milliseconds. In such experiments the sample is thermally connected to its surroundings only through its mount, so heat transport plays a central role in how the system returns to its initial phase.
This presentation covers the numerical modelling developed to support the UTEM experiments performed on Ti$_3$O$_5$ lamellae. We describe a three-dimensional heat-diffusion model that includes the first-order character of the transition and the thermal coupling between the lamella and its mount. The simulations are presented as time-dependent relaxation curves of the transformed phase fraction and as spatial maps of temperature and phase, for different excitation conditions and thermal contacts, in a form that can be compared directly with the measured diffraction data.
[1] S. Ohkoshi et al., Nature Chemistry 2, 539–545 (2010).
[2] H. Tokoro et al., Nature Communications 6, 7037 (2015).
[3] C. Mariette et al., Nature Communications 12, 1239 (2021).
[4] R. Mandal et al., Communications Materials 6, 209 (2025).
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