Figure 3. Complex oxides for emerging energy applications [2].
Mainly due to the simplicity of the governing physics, physics has not been playing a major role in recent energy-related materials researches. However, as the importance of the sustainable energy is ever more increasing, we believe that a fundamental breakthrough mechanism or novel energy material should be proposed, based on the viewpoint of physics. We intend to investigate oxide heterostructures in terms of (1) solar energy application and (2) cathode materials for batteries and solid oxide fuel cells. In particular, we intend to continue our efforts in studying ferroelectric photovoltaics or optical band gap tuning in transition metal oxides (Fig. 3) [2,3]. On the other hand, we will also study cathode materials for battery and fuel cell applications, with an emphasis on multivalency of transition metal elements. Transition metal oxides are already one of the best materials for the cathode applications, as the valence state of the transition metal elements can be easily modified by introducing or extracting oxygen ions [9]. Based on our recent studies in multivalent cobalt oxides [6,10], we aim at understanding the valence state of different transition metals in complex oxides and their influence on energy and environment related performances.
References
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[2] W. S. Choi, M. F. Chisholm, D. J. Singh, T. Choi, G. E. Jellison Jr. and H. N. Lee, “Wide bandgap tunability in complex transition metal oxides by site-specific substitution” Nat. Commun. 3, 689 (2012).
[3] W. S. Choi and H. N. Lee “Band gap tuning in ferroelectric Bi4Ti3O12 by alloying with LaTMO3 (TM = Ti, V, Cr, Mn, Co, Ni, and Al)” Appl. Phys. Lett. 100, 132903 (2012).
[4] W. S. Choi, S. Lee, V. R. Cooper, and H. N. Lee “Fractionally delta-doped oxide superlattices for higher carrier mobilities” Nano Lett. 12, 4590 (2012).
[5] A. Ohtomo & H. Y. Hwang, “A high-mobility electron gas at LaAlO3/SrTiO3” Nature 427, 423 (2004).
[6] W. S. Choi, J.-H. Kwon, H. Jeen, J. E. Hamann-Borrero, A. Radi, S. Macke, R. Sutarto, F. He, G. A. Sawatzky, V. Hinkov, M. Kim, and H. N. Lee “Strain-induced spin-states in atomically ordered cobaltites” Nano Lett. 12, 4966 (2012).
[7] W. S. Choi, D. W. Jeong, S. S. A. Seo, Y. S. Lee, T. H. Kim, S. Y. Jang, H. N. Lee, and K. Myung-Whun “Charge states and magnetic ordering in LaMnO3/SrTiO3 superlattices” Phys. Rev. B 83, 195113 (2011).
[8] S. J. Moon, H. Jin, K. W. Kim, W. S. Choi, Y. S. Lee, J. Yu, G. Cao, A. Sumi, H. Funakubo, C. Bernhard, and T. W. Noh “Dimensionality-Controlled Insulator-Metal Transition and Correlated Metallic State in 5d Transition Metal Oxides Srn+1IrnO3n+1 (n=1, 2, and ∞)” Phys. Rev. Lett. 101, 226402 (2008).
[9] M. Hibino, T. Kimura, Y. Suga, T. Kudo, and N. Misuno “Oxygen rocking aqueous batteries utilizing reversible topotactic oxygen insertion/extraction in iron-based perovskite oxides Ca1-xLaxFeO3-δ” Sci. Rep. 2, 601 (2012).
[10] H. Jeen, W. S. Choi, M. D. Biegalski, C. M. Folkman, I. C. Tung, D. D. Fong, J. W. Freeland, D. Shin, H. Ohta, M. F. Chisholm, and H. N. Lee “Epitaxial oxygen sponges: Reversible redox reaction in epitaxial strontium cobalitites” under review (2013).