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Synthesis of a metal oxide with a room-temperature photoreversible phase transition


Photoinduced phase-transition materials, such as chalcogenides, spin-crossover complexes, photochromic organic compounds and charge-transfer materials, are of interest because of their application to optical data storage. Here we report a photoreversible metal–semiconductor phase transition at room temperature with a unique phase of Ti3O5, λ-Ti3O5. λ-Ti3O5 nanocrystals are made by the combination of reverse-micelle and sol–gel techniques. Thermodynamic analysis suggests that the photoinduced phase transition originates from a particular state of λ-Ti3O5 trapped at a thermodynamic local energy minimum. Light irradiation causes reversible switching between this trapped state (λ-Ti3O5) and the other energy-minimum state (β-Ti3O5), both of which are persistent phases. This is the first demonstration of a photorewritable phenomenon at room temperature in a metal oxide. λ-Ti3O5 satisfies the operation conditions required for a practical optical storage system (operational temperature, writing data by short wavelength light and the appropriate threshold laser power).

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Figure 1: Synthesis procedure for λ-Ti3O5 nanocrystals in a SiO2 matrix.
Figure 2: Formation and crystal structure of λ-Ti3O5.
Figure 3: Magnetic and optical properties, and electronic structures of λ-Ti3O5.
Figure 4: Reversible photoinduced phase transition in λ-Ti3O5.
Figure 5: Phase transition between λ-Ti3O5 and β-Ti3O5 induced by one-shot laser pulses.
Figure 6: Mechanism of the photoinduced phase transition in λ-Ti3O5.


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This work was performed under the management of the Project to Create Photocatalyst Industry for Recycling-oriented Society supported by the New Energy and Industrial Technology Development Organization. We are grateful to T. Nuida and K. Takeda for drawing the colour figures, K. Tomono for measuring the infrared spectra, Y. Kakegawa, H. Tsunakawa and M. Adachi for collecting TEM images, S. Ohtsuka and T. Moroyama for collecting SEM images, and T. Takasaki, Y. Namatame, M. Saigo and M. Yasaka (Rigaku Corporation) for measuring the XRD patterns. We are thankful for a Grant-in-Aid for the Global COE Program, ‘Chemistry Innovation through Cooperation of Science and Engineering’ from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan, and the Center for Nano Lithography & Analysis, The University of Tokyo, supported by MEXT, Japan.

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S.O. designed and coordinated this study and contributed to all measurements and calculations, and wrote the paper. Y.T. carried out synthesis, DSC and first-principle band calculation. T.M. carried out synthesis. A.N. performed XRD measurements, Rietveld analysis and ICP-MS. F.H. carried out synthesis and TEM, SEM and SQUID measurements. K.H. contributed to the discussion. H.T. carried out synthesis and thermodynamic analysis, and carried out the photoirradiation and pressure-effect experiments. All authors commented on the manuscript.

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Correspondence to Shin-ichi Ohkoshi.

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The authors declare no competing financial interests.

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Ohkoshi, Si., Tsunobuchi, Y., Matsuda, T. et al. Synthesis of a metal oxide with a room-temperature photoreversible phase transition. Nature Chem 2, 539–545 (2010).

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