• Bulletin of the Korean Chemical Society
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• v.20 no.9
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• pp.1045-1048
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• 1999

Electronic structures calculated based upon the extended Huckel tight-binding method for Ba1-xKxBiO3 with x = 0, 0.04, and 0.4 are reported. It is noticed that the commensurate ordering of Bi 3+ and Bi 5+ is responsible for the insulating and semiconducting behavior in BaBiO3 and Ba0.96K0.04BiO4. The band gaps of 3.2 eV and 1.4 eV for the former and the latter compounds, respectively, are consistent with the experimental results. Doping in Bi 6s-block band up to x = 0.4 causes the collapse of the ordering of Bi 3+ and Bi 5+, thereby resulting in the superconductivity in the Ba0.6K0.4BiO3 compound. Strikingly, the character of oxygen contributes to the conducting mechanism than that of the bismuth. This is quite different from the cuprate superconductors in which the character of copper dominates that of oxygen.

• Bulletin of the Korean Chemical Society
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• v.19 no.12
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• pp.1283-1293
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• 1998

A solid state chemical approach to discover new mateials with enhanced thermoelectric properties is described. The aim is to construct three-dimensional bismuth chalcogenide framework structures which contain tonically interacting alkali or alkaline earth atoms. The alkali atoms tend to have soft "rattling" type phonon modes which result in very low thermal conductivity in these materials. Another desirable feature in this class of compounds is the low crystal symmetry and narrow band-gaps. Several promising materials such as BaBiTe3, KBi6.33S10, K2Bi8S13, β-K2Bi8Se13, K2.5Bi8.5Se14, Ba4Bi6Se13, Eu2Pb2Bi6Se13, Al1+xPb4-2xSb7+xSe15 (A=K, Rb), and CsBi4Te6 are described.

• Journal of the Semiconductor & Display Technology
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• v.22 no.1
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• pp.64-71
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• 2023

In this study, we investigated the effects of BiAlSiO glass composition on its glass forming range, thermal properties, and plasma resistance. The results showed that increasing the Al2O3 content suppressed the tendency for crystallization and hindered glass formation beyond a certain threshold. Bi2O3 was found to increase the content of non-bridging oxygen, resulting in a decrease in glass transition temperature and an increase in thermal expansion coefficient. Furthermore, the etching rate was found to improve with increasing Al2O3 content but decrease with increasing SiO2 content. It was concluded that the boiling point of fluorinated compounds should be considered to 900℃. Therefore, this study is expected to contribute to the understanding of the properties of BiAlSiO glass and its application to low temperature melting PRG compositions.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2004.02a
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• pp.165-169
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• 2004

It was studied on the reductive extraction between the eutectic salt and Bi metal phases. The solutes were zirconium and the rare earth elements, where zirconium was used as the surrogate for the transuranic(TRU) elements. All the experiments were performed in a glove box filled with argon gas. Two types of experimental conditions were used -high and low initial solute concentrations in salt. Li-Bi alloy was used as a reducing agent to reduce the high chemical activity of Li. The reductive extraction characteristics were examined using ICP, XRD and EPMA analysis. Zirconium was successfully separated from the rare earth elements by the reductive extraction method. The LiF-NaF-KF system was favorable among the fluoride salt systems, whereas the LiCl-KCl system was favorable among the chloride salt systems. When the solute concentrations were high, intermetallic compounds were found near the salt-metal interface.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2002.09a
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• pp.161-163
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• 2002

The BNCT(Boron Neutron Capture Therapy) facility has been developed in Hanaro(High-flux Advanced Neutron Application Reactor), a research reactor of Korea Atomic Energy Research Institute. A typical tangenial beam port is utilized with this BNCT facility. Thermal neutrons can be penetrated within the limits of the possible maximum instead of being filtered fast neutrons and gamma rays as much as possible using the silicon and bismuth single crystals. In addition to, the liquid nitrogen (LN$_2$) is used to cool down the silicon and bismuth single crystals for the increase of the penetrated thermal neutron flux. Neutron beams for BNCT are shielded using the water shutter. The water shutter was designed and manufactured not to interfere with any other subsystem of Hanaro when the BNCT facility is operated. Also, it is replaced with conventional beam port plug in order to cut off helium gas leakage in the beam port. A circular collimator, composed of $\^$6/Li$_2$CO$_3$ and polyethylene compounds, is installed at the irradiation position. The measured neutron flux with 24 MW reactor power using the Au-198 activation analysis method is 8.3${\times}$10$\^$8/ n/cm$^2$ s at the collimator, exit point of neutron beams. Flatness of neutron beams is proven to ${\pm}$ 6.8% at 97 mm collimator. According to the result of acceptance tests of the water shutter, the filling time of water is about 190 seconds and drainage time of it is about 270 seconds. The radiation leakages in the irradiation room are analyzed to near the background level for neutron and 12 mSv/hr in the maximum for gamma by using BF$_3$ proportional counter and GM counter respectively. Therefore, it is verified that the neutron beams from BNCT facility in Hanaro will be enough to utilize for the purpose of clinical and pre-clinical experiment.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.139.1-139.1
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• 2016

Multiferroic materials are of great interest because of its potential applications in the design of devices combining magnetic, electronic and optical functionalities. Among various multiferroic materials, $BiFeO_3$(BFO) is known to be one of the intensively focused mainly due to the possibility of multiferroism at device working temperature (> $200^{\circ}C$). However, leakage current and weak polarization resulting from oxygen deficiency and crystalline defect should be resolved. Furthermore the magnetic ordering of pure BFO mainly prefers to have antiferromagnetic coupling. Up to now many attempts have been performed to improve the ferromagnetic and the ferroelectric properties of BFO by doping. In this work, we investigated the effects of Ni substitution on the multiferroism of bulk BFO. Four BFO samples (a pure BFO and three Ni-doped BFO's; $BiFe_{0.99}Ni_{0.01}O_3$, $BiFe_{0.98}Ni_{0.02}O_3$ and $BiFe_{0.97}Ni_{0.03}O_3$) were synthesized by the standard solid-state reaction and rapid sintering technique. The XRD results reveal that Ni atoms are substituted into Fe-sites and give rise to phase transition of cubic to rhombohedal. By using vibrating sample magnetometer and standard ferroelectric tester, the multiferroic properties at room temperature were characterized. We found that the magnetic moment of Ni-doped BFO turned out to be maximized for 3% of Ni dopant.

• Journal of Powder Materials
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• v.22 no.4
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• pp.254-259
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• 2015

$Bi_2Te_3$ related compounds show the best thermoelectric properties at room temperature. However, n-type $Bi_2Te_{2.7}Se_{0.3}$ showed no improvement on ZT values. To improve the thermolectric propterties of n-type $Bi_2Te_{2.7}Se_{0.3}$, this research has Cu-doped n-type powder. This study focused on effects of Cu-doping method on the thermoelectric properties of n-type materials, and evaluated the comparison between the Cu chemical and mechanical doping. The synthesized powder was manufactured by the spark plasma sintering(SPS). The thermoelectric properties of the sintered body were evaluated by measuring their Seebeck coefficient, electrical resistivity, thermal conductivity, and hall coefficient. An introduction of a small amount of Cu reduced the thermal conductivity and improved the electrical properties with Seebeck coefficient. The authors provided the optimal concentration of $Cu_{0.1}Bi_{1.99}Se_{0.3}Te_{2.7}$. A figure of merit (ZT) value of 1.22 was obtained for $Cu_{0.1}Bi_{1.9}Se_{0.3}Te_{2.7}$ at 373K by Cu chemical doping, which was obviously higher than those of $Cu_{0.1}Bi_{1.9}Se_{0.3}Te_{2.7}$ at 373K by Cu mechanical doping (ZT=0.56) and Cu-free $Bi_2Se_{0.3}Te_{2.7}$ (ZT=0.51).

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.128.1-128.1
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• 2013

We investigated the correlation between electrical transport and mechanical stress in $Bi_2Te_2Se$ by using a conductive probe atomic force microscopy in an ultra-high vacuum environment. Uniform distribution of measured friction and current were observed over a single quintuple layer terrace, which is an indication of the uniform chemical composition of the surface. By measuring the charge transport of $Bi_2Te_2Se$ surface as a function of the load applied by a tip to the sample, we found that the current density varies with applied load. The variation of current density was explained in light of the combined effect of the changes in the in-plane conductance and spin-orbit coupling that were theoretically predicted. We suppose that the local density of states is modified by tip-induced strain, but topological phase still remains. We exposed a clean topological insulator surface by tip-induced indentation. The surface conductance on the indented $Bi_2Te_2Se$ surface was studied, and the role of surface oxide on the surface conductance is discussed.

• Electronic Materials Letters
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• v.14 no.6
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• pp.689-699
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• 2018

Nanostructured Ni doped $Bi_2S_3$ ($Bi_{2-x}Ni_xS_3$, $0{\leq}x{\leq}0.07$) is explored as a candidate for telluride free thermoelectric material, through a combination process of mechanical alloying with subsequent consolidation by cold pressing followed with a sintering process. The cold pressing method was found to impact the thermoelectric properties in two ways: (1) introduction of the dopant atom in the interstitial sites of the crystal lattice which results in an increase in carrier concentration, and (2) introduction of a porous structure which reduces the thermal conductivity. The electrical resistivity of $Bi_2S_3$ was decreased by adding Ni atoms, which shows a minimum value of $2.35{\times}10^{-3}{\Omega}m$ at $300^{\circ}C$ for $Bi_{1.99}Ni_{0.01}S_3$ sample. The presence of porous structures gives a significant effect on reduction of thermal conductivity, by a reduction of ~ 59.6% compared to a high density $Bi_2S_3$. The thermal conductivity of $Bi_{2-x}Ni_xS_3$ ranges from 0.31 to 0.52 W/m K in the temperature range of $27^{\circ}C$ (RT) to $300^{\circ}C$ with the lowest ${\kappa}$ values of $Bi_2S_3$ compared to the previous works. A maximum ZT value of 0.13 at $300^{\circ}C$ was achieved for $Bi_{1.99}Ni_{0.01}S_3$ sample, which is about 2.6 times higher than (0.05) of $Bi_2S_3$ sample. This work show an optimization pathway to improve thermoelectric performance of $Bi_2S_3$ through Ni doping and introduction of porosity.