• Korean Journal of Materials Research
• /
• v.5 no.2
• /
• pp.251-258
• /
• 1995

In an effort to increase the thermoelectric figure of merit by reducing the thermal conductivity, the unidirectionally solidified n-type (Bi, Pb)-Te based alloys which form a $Bi_{2}Te_{3}-PbBi_{4}Te_{7}$eutectic lamellar structure were investigated with the microstructural control at various solidification conditions. PbBi_{4}Te_{7}$ lamellae were grown on cleavage plane(0001) of $Bi_{2}Te_{3}$ and the interlamellar spacing decreased from 10.4 $\mu \textrm{m}$to 3.2$\mu \textrm{m}$ with growth velocity variation from 1.4 \times 10^{-4}$cm/sec to $8.3 \times 10^{-4}$cm/sec. Seebeck coefficient was constant, $\mid$$\alpha$$\mid$=29 $\mu$ V/K regardless of growth direction, growth velocity and temperature gradient. Electrical conductivity showed a tendency to decrease slightly with growth velocity and it parallel to growth direction was about three times as large as perpendicular direction. The figures of merit were varied differently from Seebeck coefficients and electrical conductivities depending on the growth direction, growth velocity and temperature gradients. They showed the relative increase in case of perpendicular direction compared with parallel to growth direction. It is believed to be due to the reduction of the thermal conductivity according to decrease of the interlamellar spacing.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 1994.05a
• /
• pp.42-43
• /
• 1994

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2010.03a
• /
• pp.11-11
• /
• 2010

In order to design for nano structured materials with enhanced thermoelectric properties, the alloys in the pseudo-binary $Bi_2Te_3$-PbTe system were investigated for their micro structure and thermal properties. For this synthesis the liquid alloys were cooled by water quenching method. The micro structure images were taken by using electron probe micro analyzer (EPMA). Dendritic and lamellar structures were clearly observed with the variation in the composition ratio between $Bi_2Te_3$ and PbTe. It was confirmed that a metastable compounds is $PbBi_2Te_4$ in the The $Bi_2Te_3$-PbTe system. The change in the composition increasing $Bi_2Te_3$ ratio causes to change structure from dendritic to lamellar. Seebeck coefficient of alloys 5 which the mixture rate of $Bi_2Te_3$ is 83% was measured as the highest value. In contrast, the others decreased by increasing $Bi_2Te_3$. n-type characteristics was observed at all condition except alloy 6 which $Bi_2Te_3$ ration is 91%. The power factors of all samples were calculated with Seebeck coefficient and resistivity. Also the thermal conductivity was measured by using laser flash analyzer (LFA). In this work, the microstructures and thermal properties have been measured as a function of ratio of $Bi_2Te_3$ in the $Bi_2Te_3$-PbTe system.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.23 no.6
• /
• pp.502-507
• /
• 2010

In order to design nano structured materials with enhanced thermoelectric properties, the alloys in the pseudo-binary $Bi_2Te_3$-PbTe system are investigated for their micro structure properties. For this synthesis, the liquid alloys are cooled by the water quenching method. Micro structure images are obtained by using an electron probe micro analyzer(EPMA). Dendritic and lamellar structures are clearly observed with the variation in the composition ratio between $Bi_2Te_3$ and PbTe. The increase in the $Bi_2Te_3$ composition ratio causes to change of the structure from dendritic to lamellar. The Seebeck coefficient of sample 5, in which the mixture rate of $Bi_2Te_3$ is 83%, is measured as the highest value. In contrast, the others decrease with the increase of the $Bi_2Te_3$ composition ratio. Meanwhile, p-type characteristics are observed in sample 6, at 91%-$Bi_2Te_3$ mixture rate. The power factors of the all samples are calculated with the Seebeck coefficient and resistivity.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2010.06a
• /
• pp.237-237
• /
• 2010

고효율의 열전특성을 갖는 나노 구조체 열전재료 연구의 일환으로 이종물질인 $Bi_2Te_3$-PbTe계 열전소재의 미세구조와 특성을 조사하였다. 계단식 냉각법(step cooling)를 통하여 시편을 제조 하였고, EPMA를 이용하여 시편의 미세구조를 관찰하였다. 열전소재의 상분리를 유도하기 위하여 $700^{\circ}C$에서 용융 후 3일 동안 $400^{\circ}C$로 유지시킨 후 상온까지 용융로에서 서냉하였다. EPMA를 이용하여 제조된 시편의 미세구조와 정량 분석을 하였고, 각 상의 결정구조 확인을 위하여 XRD 분석법을 이용하여 다결정의 PbTe와 $Bi_2Te_3$ 그리고 준안정상인 $PbBi_2Te_4$가 관찰 되었다. 계단식 냉각법을 통한 시편의 열전특성을 측정하였다. 이를 통하여 제조된 시편은 급속 냉각법으로 제조된 시편과 비교되었으며, 제벡계수는와 열전도도는 상온에서 각각 약 -100mV/K와 0.9W/mK로 약90%, 40%의 열전특성 향상을 확인하였다.

• Economic and Environmental Geology
• /
• v.39 no.6 s.181
• /
• pp.643-651
• /
• 2006

The Pb-Ag-Bi-S system minerals such as galena-matildite solid solutions, cosalite and heyrovskyite occur in the Nakdong As-Bi deposits. Galena-matildite solid solutions commonly coexisting with native bismuth fill in microfractures of pyrite grains and form irregular shapes. Cosalite forms composite grains including native bismuth, heyrovskyite and Bi-Te-S system minerals in the matrix of quartz vein. Matildite from the Nakdong deposits has an end member composition, $Ag_{1.07-1.11}Bi_{1.12-1.20}S_2$, and an excess concentration of $0.3{\sim}2.4$ mole % $Bi_2S_3$ compared to the stoichiomeoic value. PbS concentrations in $PbS-AgBiS_2$ solid solutions do not exceed 54 mole %. The average chemical composition of cosalite in the study area is $Pb_{1.79}Bi_{2.29}Ag_{0.12}S_5$. Pb is slightly depleted compared to the ideal composition, but the concentrations of Ag and Cu reach as much as 1.47 wt.% and 0.27 wt.%, respectively. Heyrovskyite has the chemical formula of $Pb_{5.01}Ag_{0.26}Bi_{2.70}S_9$ suggesting that there occurs the coupled substitution of $2Bi^{3+}$ for $3Pb^{2+}$ as well as that of $Ag^++Bi^{3+}$ for $2Pb^{2+}$. The genetic condition of Pb-Ag-Bi-S system minerals can be confined to the temperature of $220{\sim}270^{\circ}C$ and the pressure below 200 bars.

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

• Economic and Environmental Geology
• /
• v.21 no.4
• /
• pp.389-400
• /
• 1988

Minor elements such as Ag, As, Au, Bi, Cd, Cu, Co, Ni, Pb, Rb, Sb, Sr and Te were analyzed by atomic absorption spectrophotometry and induced coupled plasma spectrophotometry in order to investigate pathfinders for gold in quartz porphyry, granite porphyry and vein materials in Jeonjuil gold - silver mine, and in altered biotite granites and vein materials in Dukum gold - silver mine. In Dukum gold - silver mine, it is observed that Au contents have positive relation with As, Co, and Rb contents, but negative relation with Bi contents in altered biotite granites. Au contents have positive relation with Ag, As, Co and Te contents in vein materials. In Jeonjuil gold - silver mine, it is observed that Cd, Rb, Sr and Te are enriched near ore vein in quartz porphyry and granite porphyry. Au contents have positive relation with As, Cd, Cu, $Fe_2O_3$ and $K_2O$ in vein materials.

• Journal of the Korean earth science society
• /
• v.22 no.3
• /
• pp.208-222
• /
• 2001

Geochemical investigations on suspended amorphous iron oxide material from the Kwangyang gold mine and its surrounding area, Cheonnam, Korea have been carried out. The sediments samples were collected from 11 location along Kwangyang mine area and were air dried and sieved to -80 mesh. These samples consist mainly of iron, silicon and alumina. The Fe$_2$O$_3$ contents ranges from 17.9 wt.% to 72.3 wt.%. The content of Fe$_2$O$_3$ increase with decreasing Si, Al, Mg, Na, K, Mn, and Ti, whereas the contents of Te, Au, Ga, Bi, Cd, Hg, Sb, and Se increase in the amorphous stream sediments. Amorphous stream sediments have been severely enriched for As (up to 54.9 ppm), Bi (up to 3.77 ppm), Cd (up to 3.65 ppm), Hg (up to 64 ppm), Sb (up to 10.1 ppm), Cu (up to 37.1 ppm), Mo (up to 8.86 ppm), Pb (up to 9.45 ppm) and Zn (up to 29.7 ppm). At the upstream site, the Au content (up to 4.4 ppm) in the amorphous stream sediments are relatively high but those contents decrease with distance of mine location. The content of Ag (up to 0.24 ppm) were low in upstream site but those contents increase significantly in the downstream sites. The X-ray diffraction patterns of the samples have virtually no sharp and discrete peaks, indicating that some samples are amorphous or poorly-ordered. The quartz, goethite, kaolinite and illite were associated in amorphous stream sediments. The infrared spectra for amorphous stream sediments show major absorption bands due to OH stretching, adsorbed molecular water, sulfate and Fe-O stretching, respectively.

• Korean Journal of Materials Research
• /
• v.4 no.3
• /
• pp.268-279
• /
• 1994

The x-ray powtler pattern of single phase $Bi_2S_2CaCu_2O_{8+x}$ has been identified and fullyindexed using a pseudotetragonal subcell with a= 5.408, c = 30.83 $\AA$ and an incommensurate supercellwith reciprocal lattice vector, X$q^*$, given by $q^*=0.211b^*-c^*$. The x -ray powder pattern of the Pb-free110K superconductor phase "$Bi_2S_2CaCu_2O_{10+x}$" has many lines which belong t.o an incommensuratesupercell. Using elect.ron d~ffraction pImt.ographs as a indexing guide, an indexing scheme for the powderpattern has been obtained. The unit cell has a geometrically orthorhombic subcell a=5.411, b= 5.420, c=37.29(2) $\AA$. Supercell reflections have indices that are derived from the subcell k, 1 indices by addition uf$\pm q^*$, where $\pm q^*=0.211b^*-0.78c^*$The incommensurate con~ponent In the b dwection, $\delta$, is the same for both phases but on going from2212 to 2223 phase, the superlattic component in the c direction changes from commensurate($\varepsilon$=1) toincommensurate($\varepsilon$=0.78).X>$\varepsilon$=0.78).