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Ti₃O₅ exhibits a photoinduced insulator-to-metal transition (IMT) at room temperature, offering promising technological applications such as optical data storage based on the bistability of its insulating and metallic phases at the nanoscale, and thermal energy storage enabled by the transition’s large latent heat [1,2]. Understanding the mechanisms governing the transition dynamics remains a major challenge in photoinduced phase transitions.
The IMT in Ti3O5 is particularly interesting as this isosymmetric (both phases retain the same space group C2/m) transition involves a substantial unit-cell volume expansion of approximately 6%, dominated by a ~5% expansion along the c-axis, while the a- and b-axes change by only ~1% [2,3]. Previous studies of Ti3O5 have shown that photoinduced strain waves drive the phase transition in polycrystalline samples at picosecond timescales, followed by crystallite-size-dependent dynamics during heat diffusion [3,4]. These observations, together with the pronounced anisotropy of the structural changes, raise important questions regarding the dependence of the phase-transition dynamics on crystal morphology and crystallographic orientation relative to the excitation geometry. Addressing these questions requires single-crystal specimens with controlled morphologies and orientations.
In this work, we present the first study of the photoinduced IMT in single-crystal nanoscale samples using nanosecond time-resolved electron diffraction. We observe the complete transformation to the metallic phase within 10 ns at the largest fluence used. We also provide evidence of phase coexistence both during the relaxation dynamics (~10–100 μs) and at the excitation plateau, with the extent of the transformation depending on the excitation fluence. These results establish a first step towards investigating the photoinduced IMT in dedicated nanoscale specimens and demonstrate their suitability for future studies at picosecond timescales.
Before observing the photoinduced phase transition, we identified several photoinduced macroscopic sample motions, ranging from random displacements of freestanding Ti₃O₅ nanocrystals to coherent cantilever-like oscillations [5] in focused ion beam (FIB)-prepared samples. To disentangle these motions from the structural signatures of the phase transition, we implemented a pattern-matching approach analogous to those used in 4D-STEM phase and orientation mapping [6]. This method quantitatively determines the photoinduced changes in sample orientation, enabling reliable separation of macroscopic sample motion from the phase transition dynamics.
References
[1] S. Ohkoshi et al., Nat. Chem., vol. 2, no. 7, pp. 539–545, Jul. 2010, doi: 10.1038/nchem.670.
[2] H. Tokoro et al., Nat. Commun., vol. 6, no. 1, p. 7037, May 2015, doi: 10.1038/ncomms8037.
[3] C. Mariette et al., Nat. Commun., vol. 12, no. 1, p. 1239, Feb. 2021, doi: 10.1038/s41467-021-21316-y.
[4] R. Mandal et al., Commun. Mater., vol. 6, no. 1, p. 209, Sep. 2025, doi: 10.1038/s43246-025-00896-y.
[5] J. S. Baskin, H. S. Park, and A. H. Zewail, Nano Lett., vol. 11, no. 5, pp. 2183–2191, May 2011, doi: 10.1021/nl200930a.
[6] E. F. Rauch and M. Véron, Mater. Charact., vol. 98, pp. 1–9, Dec. 2014, doi: 10.1016/j.matchar.2014.08.010.
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| Figure caption | Sample layout for UED/UTEM experiment on Ti3O5 (Orange) Relative change of the (0,0,-6) lattice vector length, with the expected change expected for the β→λ transition. Red-shaded region corresponds to the coexistence of the β and λ phases respectively. |