• Journal of the Korean Ceramic Society
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• v.30 no.11
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• pp.962-966
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• 1993

Effect of Fe content on the electrical properties of Zn2Y (Ba2Zn2Fe12O22) was studied by investigating X-ray diffraction patterns, microstructure and resistivity of samples. When x(Ba2Zn2Fe12＋xO$\delta$) is between ＋1 and -1, Zn2Y single phase was obtained and electrical resistivity was inversely proportional to Fe content. The possible defect model of Zn2Y was proposed based on the observation. When x<-1 or x>1, second phase(ZnFe2O4 for x<-1, ZnFe2O4 and Ba3Zn3Fe24O41 for x>1) were observed and the electrical resistivity was inversely proportional to the sample density. The activation energy of electrical conductivity of the stoichiometric Zn2Y was 0.49eV below 20$0^{\circ}C$ and 0.07eV above 50$0^{\circ}C$.

• Journal of the Korean earth science society
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• v.32 no.6
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• pp.537-547
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• 2011

Electrical resistivity tomography surveys using boreholes were applied to reveal the cause of a catastrophic land subsidence accompanied by the excessive groundwater withdrawal in urban karst area and to map the connectivity of disseminated cavities over the study area. In order to understand the hydrogeological characteristics, resistivity using exsitu core samples, groundwater level for five boreholes, and hydraulic conductivity using slug test were measured. The hydraulic conductivity variation ranging from 0.8 to $9.3{\times}10^{-4}\;cm/s$ for five boreholes and a gentle slope of groundwater level indicated that there is no significant characteristics of hydraulic heterogeneity. Core samples of the lime-silicated rock were classified as three groups including cracked, weathered, and fresh and measured the resistivity values ranged from 103 to 161, 218 to 277, and 597 to 662 ohm-m, respectively. Drilling results that showed the cavity filled with clay materials and tomogram for this region indicated resistivity value lower than 50 ohm-m. From the inverted resistivity results for each section with five boreholes, cavity and fractured layer were distributed along the depth between 10 and 20 m overall area and cavities ranging from 4 to 6 m filled with clay materials.

• Journal of Powder Materials
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• v.17 no.2
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• pp.136-141
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• 2010

Bismuth-telluride based $(Bi_{0.2}Sb_{0.8})_2Te_3$ thermoelectric powders were fabricated by two-step planetary milling process which produces bimodal size distribution ranging $400\;nm\;{\sim}\;2\;{\mu}m$. The powders were reduced in hydrogen atmosphere to minimize oxygen contents which cause degradation of thermoelectric performance by decreasing electrical conductivity. Oxygen contents were decreased from 0.48% to 0.25% by the reduction process. In this study, both the as-synthesized and the reduced powders were consolidated by the spark plasma sintering process at $350^{\circ}C$ for 10 min at the heating rate of $100^{\circ}C/min$ and then their thermoelectric properties were investigated. The sintered samples using the reduced p-type thermoelectric powders show 15% lower specific electrical resistivity ($0.8\;m{\Omega}{\cdot}cm$) than those of the as-synthesized powders while Seebeck coefficient and thermal conductivity do not change a lot. The results confirmed that ZT value of thermoelectric performance at room temperature was improved by 15% due to high electric conductivity caused by the controlled oxygen contents present at bismuth telluride materials.

• Current Photovoltaic Research
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• v.5 no.4
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• pp.109-112
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• 2017

Various wt. ratios of indium were doped to the poly(3,4-ethylenedioxythiophene)-poly(styreneswulfonate) (PEDOT:PSS) to enhance the conductivity and transmittance. The transmittance of the films increased with increasing the amount of indium. The field emission scanning electron microscope (FESEM) image of 2.54 wt. % of indium doped PEDOT:PSS film shows large number of aggregated indium particles. However, more than 2.54 wt. % of indium doped PEDOT:PSS films showed reduced aggregated indium particles. Moreover, 4.47 wt. % of indium doped PEDOT:PSS film showed no aggregated particles. The resistivity of pure PEDOT:PSS film showed $880k{\Omega}{\cdot}cm$. The resistivity of 1.03 wt. % indium doped film reduced approximately 26 times compared with pure PEDOT:PSS film. The resistivity of indium doped film further reduced with increasing the amount of indium, which showed approximately $0.55k{\Omega}{\cdot}cm$ for the PEDOT:PSS film doped 4.47 wt. % of indium.

• Smart Structures and Systems
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• v.7 no.1
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• pp.27-40
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• 2011

Geopolymer concrete is finding a growing number of niche applications in the field of civil engineering due to its high compressive strength and strength gain rate, retainage of structural properties in elevated temperature environments, chemical stability in highly acidic conditions and environmental benefits. Combining the above mentioned characteristics with induced electrical conductivity, could enable geopolymer cement to serve as a smart and sustainable cementitious material suitable for health monitoring of civil structures. Carbon fibers were added to fresh geopolymer and OPC (ordinary Portland cement) mixes to enhance their electrical conductivities. AC-impedance spectroscopy analysis was performed on the specimens with fiber fraction ranging from 0.008 to 0.8 with respect to the weight of cementitious binder, to measure their electrical resistivity values and to determine the maximum beneficial fiber content required to attain electrical percolation. Experimental observations suggest that CFR-geopolymer cement exhibits superior performance to CFR-OPC in terms of conducting electrical current.

• Korean Journal of Materials Research
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• v.25 no.12
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• pp.678-682
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• 2015

The electrical property of polymer matrix composites with added carbon powder is studied based on the temperature dependency of the conduction mechanism. The temperature coefficient of the resistance of the polymer matrix composites below the percolation threshold (x) changed from negative to positive at 0.20 < x < 0.21; this trend decreased with increasing of the percolation threshold. The temperature dependence of the electrical property(resistivity) of the polymer matrix composites below the percolation threshold can be explained by using a tunneling conduction model that incorporates the effect of the thermal expansion of the polymer matrix composites into the tunneling gap. The temperature coefficient of the resistance of the polymer matrix composites above the percolation threshold has a positive value; its absolute value increased with increasing volume fraction of carbon powder. By assuming that the electrical conduction through the percolating paths is a thermally activated process and by incorporating the effect of thermal expansion into the volume fraction of the carbon power, the temperature dependency of the resistivity above the percolation threshold can be well explained without violating the universal law of conductivity.

• Applied Microscopy
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• v.47 no.3
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• pp.121-125
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• 2017

This study deals the prediction of temperature effect on low-frequency dispersion of alternating current (AC) conductivity spectra of composite materials based on copolymer reinforced with carbon black (CB) particles. A sample of ethylene butylacrylate loaded with 13% of CB particles were prepared and investigated using the impedance spectroscopy representation in the frequency range from 40 Hz to 0.1 MHz and temperature range from $20^{\circ}C$ to $125^{\circ}C$. The dielectric constant, ${\varepsilon}^{\prime}$, and dielectric losses, ${\varepsilon}^{{\prime}{\prime}}$, were found to decrease with increasing frequency. The frequency dependence of the AC conductivity follows the universal power law with a large deviation in the high frequency region, the positive temperature coefficient in resistivity effect has been observed below the melting temperature which makes this composite potentially remarkable for industrial applications.

• Journal of the Korean institute of surface engineering
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• v.44 no.6
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• pp.264-268
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• 2011

The Molybedenium thin film is generally used on back contact material of CIGS solar cell due to low electrical resistivity and stable thermal expansion coefficient. The Mo thin films deposited on si wafer by the magnetron sputtering method. The research focused on the variation of electrical resistivity of films which deposited with various working pressure at the target power of 2.0 kW(8.4 W/). The lowest resistivity of Mo thin film showed $9.0{\mu}O$-cm at pressure of 1.5 mTorr. However, working pressure increasing up to 50 mTorr, resistivities were highly increased. The results showed that the conductivity of Mo films depended on growing structures and defects in deposition process. Surface morphology, porosity, grain size, oxidation, and bonding structures were analysed by SEM, AFM, spectroscopic ellipsometry (SE), XRD, and XPS.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2004.09a
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• pp.262-265
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• 2004

The purpose of this study is to investigate environmental characteristics and in-situ hydraulic conductivity by eco cone penetration system. The underground environments and permeability of site was investigated and analyzed by this eco cone system. The electrical resistivity, pH, ORP, temperature and hydraulic conductivity were measured by eco cone penetration system. This eco cone penetration system provides a continuous environment and permeability profiles in underground, and provides reliable results for investigation of normal and contaminated ground.

• Explosives and Blasting
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• v.34 no.4
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• pp.19-27
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• 2016

Much care should be taken when electric caps are used in blast site than when non-electric initiation systems are used. This is because electric caps can cause premature firing or misfires if stray currents of high magnitude flow into the blasting circuit. If the rock has higher electrical conductivity or lower electrical resistivity, such risks will be increased because the rock will provide more passages for the stray currents to flow into the blasting circuit. In this study, several rock samples obtained at a blast site were tested for electrical resistivity to decide whether electric caps could be used or not in the site. The measured electrical resistivity was $39{\sim}47{\Omega}{\cdot}m$ for the rock samples that had a higher content of metal sulfides. Contrary, the resistivity was $15000{\sim}21000{\Omega}{\cdot}m$ for ordinary rocks. Especially, in the case of the rock of electric resistivity of $39{\Omega}{\cdot}m$, only 2-V electric potential enables a stray current to flow through the rock of 1-m length, which can cause the premature firing of a detonator whose initiation current is 0.4 A. This result shows that electric initiation system should not be used in the site because rocks containing much amount of metal sulfides are widely distributed there.