Papers by Author: G.S. Choi

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Authors: Il Ho Kim, Jung Il Lee, G.S. Choi, J.S. Kim
Abstract: Thermal, electrical and mechanical properties of high purity niobium and tantalum refractory rare metals were investigated to evaluate the physical purity. Higher purity niobium and tantalum metals showed lower hardness due to smaller solution hardening effect. Temperature dependence of electrical resistivity showed a typical metallic behavior. Remarkable decrease in electrical resistivity was observed for a high purity specimen at low temperature. However, thermal conductivity increased for a high purity specimen, and abrupt increase in thermal conductivity was observed at very low temperature, indicating typical temperature dependence of thermal conductivity for high purity metals. It can be known that reduction of electron-phonon scattering leads to increase in thermal conductivity of high purity niobium and tantalum metals at low temperature.
Authors: K.W. Jang, Il Ho Kim, J.I. Lee, G.S. Choi
Abstract: Te doping effect on the thermoelectric properties of solid solution was investigated. 2at% Te doping was found to be most effective to improve the dimensionless figure of merit, ZT, of pseudo-binary CoSb3-4mol%Zn4Sb3. Maximum ZT of 0.69 was obtained at 450K in CoSb3- 4mol%Zn4Sb3 doped with 2at% Te. Heavy doping of Te above 3at% caused thermal conductivity to increase very high because of the formation of metallic CoSb2 phases and thus did not improve ZT.
Authors: Il Ho Kim, G.S. Choi, M.G. Han, Ji Soon Kim, Jung Il Lee, Soon Chul Ur, Tae Whan Hong, Sung Lim Ryu, Young Geun Lee
Abstract: CoSb3 compounds were prepared by the arc melting and their thermoelectric properties were investigated at 300K-600K. Annealing effects were examined and they were correlated to phase transformation and homogenization. Undoped CoSb3 showed p-type conduction and intrinsic semiconducting behavior at all temperatures examined. Thermoelectric properties were changed with constituent phases because α-CoSb2, β-CoSb and Sb are metallic or semimetallic phases while δ-CoSb3 is semiconducting phase. Thermoelectric properties were remarkably improved by annealing in vacuum and they were closely related to phase transitions. Single phase δ-CoSb3 was successfully obtained by annealing at 400°C for 24hrs.
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