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Satoshi Okajima,Yasuyuki Shimura,Takahiro Onimaru 한국물리학회 2023 새물리 Vol.73 No.12
When spins of s = 1/2 form a triangular lattice and antiferromagnetic interactions work between them, magnetic order is suppressed due to geometrical frustration. Our research is centered on Yb-based semiconductors Yb₂Cu<SUB>2n</SUB>S<SUB>n+3</SUB> (2 ≤ n ≤ 5) which crystallize in a trigonal CaAl₂Si₂-type structure. These semiconductors feature a defective triangular lattice made up of Yb ions. We synthesized two polycrystalline Yb₂Cu<SUB>2n</SUB>S<SUB>n+3</SUB>, with n values of 2.2 and 3.6. The former has a defect rate of 24% for Yb sites, while the latter has a defect rate of 45%. The specific heat and magnetization were measured down to 0.4 and 1.8 K, respectively. For n = 2.2, there was no indication of a phase transition. On the other hand, for n equal to 3.6, the specific heat exhibits a cusp at T₁ = 4.1 K and a peak at T₂ = 2.3 K. It is suggested that the deficiency of Yb sites in the triangular lattice induces phase transitions as a way to release geometrical frustration.
Zhang, Yue-Biao,Furukawa, Hiroyasu,Ko, Nakeun,Nie, Weixuan,Park, Hye Jeong,Okajima, Satoshi,Cordova, Kyle E.,Deng, Hexiang,Kim, Jaheon,Yaghi, Omar M. American Chemical Society 2015 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.137 No.7
<P>Metal-organic framework-177 (MOF-177) is one of the most porous materials whose structure is composed of octahedral Zn4O(-COO)(6) and triangular 1,3,5-benzenetribenzoate (BTB) units to make a three-dimensional extended network based on the qom topology. This topology violates a long-standing thesis where highly symmetric building units are expected to yield highly symmetric networks. In the case of octahedron and triangle combinations, MOFs based on pyrite (pyr) and rutile (rtl) nets were expected instead of qom. In this study, we have made 24 MOF-177 structures with different functional groups on the triangular BTB linker, having one or more functionalities. We find that the position of the functional groups on the BTB unit allows the selection for a specific net (qom, pyr, and rtl), and that mixing of functionalities (-H, -NH2, and -C4H4) is an important strategy for the incorporation of a specific functionality (-NO2) into MOF-177 where otherwise incorporation of such functionality would be difficult. Such mixing of functionalities to make multivariate MOF-177 structures leads to enhancement of hydrogen uptake by 25%.</P>