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Novel n-type Zintl phase thermoelectric materials: The Ca5−xRExAl2Sb6 (RE = Pr, Sm) system
이준수,서나은,연성범,유태수 대한화학회 2023 Bulletin of the Korean Chemical Society Vol.44 No.8
Two novel n-type Zintl thermoelectric materials of Ca4.97(1)Pr0.03Al2Sb6 and Ca4.94(2)Sm0.06Al2Sb6 were synthesized with the addition of two types of trivalent rare-earth metals dopants and characterized by powder and single crystal x-ray diffraction analyses. Two title compounds adopted the orthorhombic Ca5Ga2As6-type phase and contained seven crystallographically unique atomic positions including one particular Ca/Pr or Ca/Sm mixed-site. The crystal structure can be described as a combination of the one-dimensional (1D) 1 ∞[Al2Sb4Sb4=2] infinite chains and the cationic elements in between the 1D chains. Electrical transport property measurements proved that Ca4.97 (1)Pr0.03Al2Sb6 and Ca4.94(2)Sm0.06Al2Sb6 were indeed novel n-type Zintl phase semiconductors with the maximum electrical conductivities of 69.51 and 75.51 S/cm at 846 K and the Seebeck coefficients of 43.26 and29.00 μV/K at 703 K, respectively. Density functional theory calculations proved that the successful n-type doping should be attributed to a small margin of slight antibonding states near EF on the Sb1 Sb1 crystal orbital Hamilton population (COHP) curve.
이준수,홍영진,연성범,문도현,유태수 대한화학회 2021 Bulletin of the Korean Chemical Society Vol.42 No.4
Two dopants with quinary Zintl phases Ca1.02Yb3.98Al1.48In0.52Sb6 and Ca5Al1.73In0.27Sb5.44Sn0.56 were synthesized by arc melting followed by annealing to evaluate the possibility of exploiting them as p-type thermoelectric materials. The phase purity and crystal structures were carefully determined by powder X-ray diffraction and single-crystal X-ray diffraction analyses, and the refined isotypic Ca5Ga2Sb6-type structures were described as an assembly of the one-dimensional anionic frameworks and the space-filling cationic sites. The newly added cationic Yb and anionic Sn showed specific site-preferences, which was elucidated by either the size-factor or the electronic-factor criterion. Moreover, these dopings were closely related to the phase transition of Ca1.02Yb3.98Al1.48In0.52Sb6 and the possible increase in electrical transport property of Ca5Al1.73In0.27Sb5.44Sn0.56. In particular, the thorough study for band structure of the Sndoped compound proves that the increased band extrema and degeneracies in the valence band can increase Seebeck coefficients, and the introduced atomic mixtures can lower thermal conductivities by increasing phonon scattering of title compounds.
이인범,최병훈,문연성,황정민,In-Bum Lee Candidate,Byung-Hun Choi Candidate,Yeon-Seong Mun,Jeong-Min Hwang 대한안과학회 2005 대한안과학회지 Vol.46 No.6
Purpose: In order to investigate the incidence of relative afferent pupillary defect (RAPD) in normal adolescence and if there is any interocular difference in the case with RAPD. Methods: Fifty-eight adolescence in 14 to 36 years of age who showed normal findings on measurement of visual acuity, intraocular pressure, slit lamp examination, and funduscopic examination except refractive errors underwent swinging flashlight test and infrared pupillography. The case with RAPD further underwent optical coherence tomography, color vision test, Humphrey visual field test, and Bryngelson test (hole-in-the-card test). Results: One out of 58 cases, in whom more pronounced myopic astigmatism and lower mean deviation on Humphrey visual field test within normal limits were found, showed RAPD in the dominant right eye with swinging flashlight test and infrared pupillography. Conclusions: The incidence of RAPD in normal adolescence was 1.7%. Myopic astigmatism was higher in the eye with RAPD.