Lee Hsun Lecture Series
Topic: Development of functional green materials based on metal complexes and metal oxides
Speaker: Prof. Shin-ichi Ohkoshi
Department of Chemistry, School of Science, University of Tokyo
Time: 10:00-12:00, (Mon.) Sept. 22nd, 2025
Venue: Room 403, Shi Changxu Building, IMR CAS
Abstract:
Functional materials utilizing phase transition phenomena are highly attractive for the control of physical properties. We have developed a variety of phase transition materials based on cyanido-bridged metal
complexes, including photo-switchable superionic conductors1 and light-induced spin-crossover ferromagnets.2,3 Additionally, we have explored functional metal oxides such as epsilon iron oxide (ε-Fe2O3) 4,5and lambda-trititanium pentoxide (λ-Ti3O5). 6-8 In the present lecture, I will introduce our recent research progress on such novel functional materials contributing to green transformation.
Giant barocaloric ef ect in Prussian blue analogue: We developed a rubidium cyanido-bridged manganese–iron–cobalt complex (RbMn{[Fe(CN)6]0.92[Co(CN)6]0.08}·0.3H2O) that shows a charge-transfer phase transition with thermal hysteresis. The transition from the high-temperature to low-temperature phase can also be induced by pressure. This compound exhibits a large barocaloric effect, with adiabatic temperature changes of 74 K at 340 MPa and 85 K at 560 MPa. Direct temperature measurements revealed changes of +44 K upon pressure application and −31 K upon pressure release, with excellent reversibility over 100 cycles.9
Hard magnetic ferrite, ε-Fe2O3: We succeeded in obtaining pure ε-Fe2O3 and found that it shows a huge coercive field of over 20 kOe at room temperature and high-frequency millimeter wave absorption at 182 GHz. The physical properties can be controlled by substituting Fe3+ with other transition metal ions.4 ε-Fe2O3 can also be downsized to sub-ten nanometer size maintaining its magnetic properties due to its strong magnetic anisotropy, which opens the possibility of the present material to be used for high-density magnetic recording. A novel magnetic recording method of using millimeter wave for assisting magnetic pole flip has also been demonstrated.5
Heat-storage ceramic, λ-Ti3O5: λ-Ti3O5 was discovered by nanoparticle synthesis of Ti3O5. Thermodynamic analysis suggests that λ-Ti3O5 is a trapped phase at a local energy minimum. Light irradiation causes a
reversible switching between this trapped state (λ-Ti3O5) and the other energy minimum state (β-Ti3O5).6 Furthermore, we have reported that the reversible switching is also induced by other external stimulation such as pressure, and have found that this material exhibits high performance heat-storage properties.7,8
Time evolution dynamics of phase transition materials: Pump-probe spectroscopy measurements have been conducted to investigate the dynamics of the phase transition in materials such as λ-Ti3O5 and RbMn[Fe(CN)6].10-12
References (1) S. Ohkoshi et al., Nature Chemistry, 12, 338 (2020). (2) S. Ohkoshi et al., Nature Chemistry, 3, 564 (2011). (3) S. Ohkoshi et al., Nature Photonics, 8, 65 (2014). (4) A. Namai, et al., Nature Communications, 3, 1035 (2012). (5) S. Ohkoshi, et al., Adv. Mater., 32, 2004897 (2020). (6) S. Ohkoshi et al., Nature Chemistry, 2, 539 (2010). (7) Y. Nakamura et al., Science Advances, 6, 5264 (2020). (8) H. Tokoro, et al., Nature Communications, 6, 7037 (2015). (9) S. Ohkoshi, et al., Nature Communications, 14, 8466 (2023). (10) C. Mariette, et al., Nature Communications, 12, 1239 (2021). (11) M. Hervé, et al., Nature Communications, 15, 267 (2024). (12) K. Nakamura, et. al., Nature Communications, 16, 5012 (2025).
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