• Coupled systems mechanics
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• v.11 no.2
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• pp.151-166
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• 2022

Peltier cells have low efficiency, but they are becoming attractive alternatives for affordable and environmentally clean cooling. In this line, the current article develops closed-form and semianalytical solutions to improve the temperature distribution of Bi₂Te₃ thermoelements. From the distribution, the main objective of the current work-the optimal electric intensity to maximize cooling-is inferred. The general one-dimensional differential coupled equation is integrated for linear and quadratic geometry of thermoelements, under temperature constant properties. For a general shape, a piece-wise solution based on heat flux continuity among virtual layers gives accurate analytical solutions. For variable properties, another piece-wise solution is developed but solved iteratively. Taking advantage of the formulae, the optimal intensity is directly derived with a minimal computational cost; its value will be of utility for more advanced designs. Finally, a parametric study including straight, two linear, barrel, hourglass and vase geometries is presented, drawing conclusions on how the shape of the thermoelement affects the coupled phenomena. A specially developed coupled and non-linear finite element research code is run taking into account all the materials of the cell and using symmetries and repetitions. These accurate results are used to validate the analytical ones.

• Proceedings of the Korean Magnestics Society Conference
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• 2017.05a
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• pp.165-166
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• 2017

• Proceedings of the Materials Research Society of Korea Conference
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• 1992.05a
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• pp.1-1
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• 1992

Shape Memory Alloys have attracted the interest of a great number of researchers in the world, and Mexico is not the exception. Research in this field started ten years ago, and is actually an active line covering the classical Cu-based and Ti-Ni alloys, but also the new Fe-based alloys. Although more basic studies have been performed at the present time, interest for applied research and technological goals is increasing. In this work we present a series of studies carried on these Shape Memory Alloys by the groups in Mexico, and explain what the interest of our groups are in the next future in this are of the Materials Science. Interdisciplinary work has been necessary in the characterization of the different alloys, and multiple techniques have been used, like Mossbauer spectroscopy, thermoelectric power, electron microscopy, ultrasound techniques, neutron and x-ray diffraction, calorimetry, among others. Collaboration With other groups in Europe and in the United States have become highly useful and productive, and some examples of such activities are also reported.

• Korean Journal of Materials Research
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• v.7 no.5
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• pp.374-380
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• 1997

열전재료 분말을 AI관에 진공봉입하고 형틀가입한 후 소결하는 새로운 방법으로 n형 B $i_{2}$T $e_{2.4}$S $e_{0.6}$를 제조하여 소결조건에 따른 소결성과 열전특성을 조사.분석하였다. AI은 소결시 열전재료와 반응하지 않아 보호 용기로 적합하였으며, 평균입도 195$\mu\textrm{m}$의 분말을 사용하여 성형압 280 MPa, 온도 400에서 50$0^{\circ}C$에서 소결할 경우 성능지수는 1.9x $10^{-3}$K였다.다.

• Korean Journal of Metals and Materials
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• v.48 no.2
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• pp.175-179
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• 2010

We investigated the thermal conductivity of individual single-crystalline PbTe nanowires grown by chemical vapor transport method. Suspended MEMS was utilized to precisely measure the thermal conductivity of an individual nanowire. The thermal conductivity of a PbTe nanowire with diameter of 292 nm was measured to be $1.8W/m{\cdot}K$ at 300 K, which is about two thirds of that of bulk PbTe. This result indicates that the thermal conduction through a PbTe nanowire is effectively suppressed by the enhanced phonon boundary scattering. As the diameter of a PbTe nanowire decreases, the corresponding thermal conductivity linearly decreases.

• Applied Chemistry for Engineering
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• v.1 no.1
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• pp.83-90
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• 1990

The semiconducting $(Pb_1\;_xSn_x)_1$ $_yTe_y$, one of the low - temperature thermoelectric materials, has been prepared and its chemical composition and nonstoichiometry has been analyzed. The content of Pb in the specimens was determined by the complexometric back - titration method with EDTA and Pb(II) standard solutions. Te - content was analyzed with the redox titration method. The electrical conductivity and the thermoelectric power have also been measured by the DC 4 - probe and the heat-pulse technique, respectively. All of the specimens showed a nonstoichiometric behavior in their chemical compositions (Te excess), thus gave rise to a p - type semiconducting property, and the nonstoichoimetry became bigger as the Sn - content increased. The thermoelectric power vs. temperature results have been analyzed upon the basis of the Fermi level vs. temperature profiles in the saturation regime. The specimen of x=0.1 evolved a transition from p - to n - type property at about 670K, which has been explained by the fact that the mobility of electrons is bigger than that of holes in the temperature range of the intrinsic regime.

• Journal of the Microelectronics and Packaging Society
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• v.15 no.3
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• pp.1-8
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• 2008

Effects of annealing process in a reduction ambient on thermoelectric properties of the $(Bi,Sb)_{2}Te_3$ thin films prepared by thermal evaporation have been investigated. With annealing at $300^{\circ}C$ for 2 hrs in a reduction ambient(50% $H_2$+50% Ar), the crystallinity of the $(Bi,Sb)_{2}Te_3$ thin films were substantially improved with remarkable increase in the grain size. Seebeck coefficients of the $(Bi,Sb)_{2}Te_3$ thin films increased from$\sim90{\mu}V/K$ to $\sim180{\mu}V/K$ with annealing in the reduction ambient due to decrease in the hole concentration. Power factors of the $(Bi,Sb)_{2}Te_3$ thin films were remarkably improved for $5\sim16$ times with annealing in the reduction atmosphere. After annealing in the reduction ambient, a $(Bi,Sb)_{2}Te_3$ evaporated film exhibited a maximum power factor of $18.6\times10^{-4}W/K^{2}-m$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.11
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• pp.1133-1137
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• 2011

A novel technique for the fabrication of a glass micropipette-based thermal sensor was developed utilizing inexpensive thermocouple materials. Thermal fluctuation with a resolution of ${\pm}0.002$ K was measured using the fabricated thermal probe. The sensors comprise unleaded low-melting point solder alloy (Sn) as a core metal inside a borosilicate glass pipette coated with a thin film of Ni, creating a thermocouple junction at the tip. The sensor was calibrated using a thermally insulated calibration chamber, the temperature of which can be controlled with a precision of ${\pm}0.1$ K and the thermoelectric power (Seebeck coefficient) of the sensor was recorded from 8.46 to $8.86{\mu}V$/K. The sensor we have produced is both cost-effective and reliable for thermal conductivity measurements of micro-electromechanical systems (MEMS) and biological temperature sensing at the micron level.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.3
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• pp.135-141
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• 2013

Mechanical alloying was carried out to produce $CrSi_2$ thermoelectric compound using a mixture of elemental $Cr_{33}Si_{67}$ powders. An optimal milling and heat treatment conditions to obtain the single phase of $CrSi_2$ compound with fine microstructure were investigated by X-ray diffraction and differential scanning calorimetry measurement. $CrSi_2$ intermetallic compound with a grain size of 70 nm could be obtained by MA of $Cr_{33}Si_{67}$ powders for 70 hours and subsequently annealed at $650^{\circ}C$. Consolidation of the MA powders was performed in a spark plasma sintering (SPS) machine using graphite dies at $600{\sim}1000^{\circ}C$ under 60 MPa. The shrinkage of MA samples during SPS consolidation process increased gradually with increasing temperature up to $1000^{\circ}C$ and relatively significant at about $600^{\circ}C$. We tend to believe that these behaviors are deeply related to form a $CrSi_2$ compound during heating process, as can be realized from the DSC measurement. Electrical conductivity and Seebeck coefficient of sintered bodies were measured up to $900^{\circ}C$. Seebeck coefficient and power factor of $Cr_{33}Si_{67}$ compact prepared by MA and SPS at $1000^{\circ}C$ showed the maximum value of $125{\mu}V/K$ at $400^{\circ}C$ and $4.3{\times}10^{-4}W/mK^2$ at $350^{\circ}C$, respectively.

• Korean Journal of Materials Research
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• v.8 no.11
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• pp.1055-1060
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• 1998

Thermoelectric properties of ($Pb_{1-x}Sn_x$)Te ($0\leq{x}\leq{0.4}$) alloys, fabricated by mechanical alloying and hot pressing, were investigated with variation of the SnTe content. For the hot-pressed PbTe and ($Pb_{0.9}Sn_{0.1}$)Te. transition from p-type to n-type occurred at $200^{\circ}C$ and $300^{\circ}C$, respectively. However, the specimens containing SnTe more than 0.2mole exhibited p-type conduction up to 450'C. In extrinsic conduction region, the Seebeck coefficient and electrical resistivity of the hot-pressed ($Pb_{1-x}Sn_x$)Te decreased with increasing the SnTe content. The temperature at which the hot-pressed (Pbl-,Sn,)Te exhibited a maximum figure-of-merit was shifted to higher temperature with increasing the SnTe content The hot-pressed (Pbo ,Sno dTe exhibited a maximum figure-of-merit of $0.68\times10_{-3}/K$ at $200^{\circ}C$.