| 研究実績の概要 |
During the last year, 6 new oxyhydrides compounds have been prepared through topochemical exchange with CaH2 for the first time: LnHO with Ln = Sm, Gd, Tb, Dy, Ho, and Er. While cation order-disorder transitions have been achieved in a wide range of materials and provide crucial effects in various physical and chemical properties, anion analogues are scarce. Here we have expanded the number of known lanthanide oxyhydrides, LnHO (Ln = La, Ce, Pr, Nd), to include Ln = Sm, Gd, Tb, Dy, Ho, and Er, which has allowed the observation of an anion order-disorder transition from the anion-ordered fluorite structure (P4/nmm) for larger Ln3+ ions (La-Nd) to a disordered arrangement (Fm3m) for smaller Ln3+ (Sm-Er). The presence or absence of cation order in complex oxides can have a decisive impact on their chemical and physical properties. However, unlike the cation case, examples of “controlling” anion order and disorder (i.e., inducing anion order-disorder transitions) are scarce, aside from anion vacancy order-disorder transitions, and therefore constitute an important challenge.
So far, one paper has been submitted and accepted in the Journal of American Chemical Society.
T. Broux, et al., Chemical pressure-induced anion order-disorder transition in LnHO enabled by hydride size flexibility, J. Am. Chem. Soc. 2018, 140, 11170-11173
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
2: おおむね順調に進展している
理由
Their ionic conductivities and the ammonia synthesis catalytic activity will be estimated for potential application. The discovery of a new series of oxyhydrides is interesting in terms of catalysis. Recently, a number of novel catalyst supports for the Haber-Bosch synthesis of NH3 have been reported, centering on hydrides and electrides. Thanks to unique Kageyama-sensei laboratory facilities, we have been able to make progression in the search for new materials.
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| 今後の研究の推進方策 |
Structural analysis of LnHO series reveals that with the increase of Ln3+ radius (application of negative chemical pressure), the oxide anion in the disordered phase becomes too under-bonded, which drives a change to an anion-ordered structure, with smaller OLn4 and larger HLn4 tetrahedra, demonstrating that the size flexibility of hydride anions drives this transition. Such anion ordering control is crucial regarding applications that involve hydride diffusion such as catalysis and electrochemical solid devices. In the future, we want to search for high-pressure polymorphs related to the LnHO composition, as the chemical pressure is already responsible for unique features in this material.
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