• Journal of the Korean Magnetics Society
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• v.18 no.2
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• pp.75-78
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• 2008

$AB_2X_4$(A, B=Transition Metal, X=O, S, Se) are cubic spinel normal ferrimagnets, in which M ions occupy the tetrahedral sites and Cr ions occupy the octahedral sites. Recently, they have been investigated for behaviour of B site ions and A-B interaction. Polycrystalline $[Co_{0.9}Zn_{0.1}]_A[Cr_{1.98}{^{57}Fe_{0.02}}]_BO_4$ compound was prepared by wet-chemical process. The ferrimagnetic transition was observed around 90K. $M\"{o}ssbauer$ absorption spectra at 4.2K show that the well-developed two sextets are superposed with small difference in hyperfine fields($H_{hf}$). The hyperfine fields of $CoCr_{1.98}{^{57}Fe_{0.02}}O_4$ and $Co_{0.9}Zn_{0.1}Cr_{1.98}{^{57}Fe_{0.02}}O_4$ were determined to be 488, 478 kOe and 486, 468 kOe, respectively. We notice that the one of the magnetic hyperfine field values changes with Zn ion substitution. These results suggest the incommensurate states and spin-reorientation temperature($T_S=18K$) changes with Zn ions substitution below spin-reorientation temperature($T_S=28K$) of $CoCr_{1.98}{^{57}Fe_{0.02}}O_4$

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.16-16
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• 2009

ZnO($Zn_{1+x}O$)는 n-type 반도성 세라믹스로 우수한 전기적, 광학적, 화학적 특성을 갖고 있어 바리스터, 투명 전도막, 화학 및 바이오 센서, UV light emitter 등 다양한 용도로 사용되고 있다. 또한 ZnO에 각종 천이 금속 산화물을 일정량 첨가함에 따라 발생하는 결함준위와 입계 특성의 변화에 대한 연구가 활발히 진행되고 있다. 다양한 천이 금속 산화물의 첨가에 따른 전기적 광학적 특성의 변화에 대한 결과들이 많이 보고되고 있지만 서로 상충되거나 해석상 다소 어려운 것으로 알려져 있다. 따라서 본 연구에서는 ZnO에 $Cr_2O_3$를 2.0 at% 첨가하여 Cr 첨가에 따른 ZnO의 결함준위와 입계 특성 변화에 대하여 각종 유전함수($Z^*$, $Y^*$, $M^*$, $\varepsilon^*$, and $tan{\delta}$)를 이용하여 고찰하였다 ZnO에 Cr을 첨가할 경우 결함 중 장범위 쿨롱 인력에 의한 결함(0.13~0.18 eV)이 ~100K 영역에서 나타났으며, ZnO 내 결함 중 대표적인 $Zn_j$와 $V_o$는 서로 겹쳐서 나타났다. 이들 중첩된 결함에 대하여 각종 유전함수를 이용할 경우 서로 분리해 낼 수 있는 강점이 있음을 논하였다. 또한 각 결함준위가 강는 정전용랑(C)과 저항(R)을 impedance-modulus spectroscopy를 이용하여 구한 결과, 소결온도가 높아질수록 정전용량은 증가하였으며, 측정온도가 놓아질수록 높아지는 경향을 나타내었다. 입계의 정전용량은 소결온도가 높아질수록 높아 지지만 측정온도가 높아질수록 낮아지는 경향을 나타내었다. 각 저항값은 소결온도 및 측정온도가 높아질수록 지수적으로 감소하였다. 또한 분포함수를 이용하여 입계 안정성에 대하여 고찰하였다.

• Korean Journal of Materials Research
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• v.1 no.2
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• pp.65-70
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• 1991

The effect of inclusion particles on the microstructure development and electrical characteristics in the systems $ZnO-Bi_2O_3-CoO-Sb_2O_3\;and\;ZnO-Bi_2O_3-CoO-Sb_2O_3-Cr_2O_3 were investigated. The growth of ZnO grains, which was controlled by the spinel particles during sintering, decreased with increasing amount of spinel particles. Addition of $Cr_2O_3(0.5mol\%) increased the breakdown voltage without affecting the non-linear characteristics. The calculated barrier voltage of the $ZnO-Bi_2O_3-CoO-Sb_2O_3\;-and\;ZnO-Bi_2O_3-CoO-Sb_2O_3-Cr_2O_3$ systems were about 3.1V and 2.9V, respectively.

• Journal of the Korean Ceramic Society
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• v.38 no.8
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• pp.732-739
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• 2001

산업부산자원으로부터 유입되는 중금속이 시멘트 수화반응에 미치는 영향에 대하여 연구하였다. 출발물질은 순수시약을 사용하여 $C_3$S와 $C_2$S 조성으로 배합하고 여기에 Zn, Cu, Cr의 중금속 산화물을 1000ppm, 2000ppm, 3000ppm 첨가하여 150$0^{\circ}C$에서 1시간 소결하여 중금속의 고용분배, 결정구조, 용출상태 그리고 수화열을 관찰하였다. 중금속중 Zn는 $C_3$S와 간극질에 집중 고용되고 Cu는 간극물질에 집중 고용되며 Cr은 $C_3$S와 $C_2$S에 집중 고용되었다. 광학현미경 및 XRD 관찰결과 중금속 함량별로 $C_3$S와 $C_2$S의 결정상에는 큰 영향이 없는 것으로 나타났다. 그리고 7일간 수화시 Zn는 40~50%, Cu와 Cr은 전량 용출되었다. Conduction calorimeter 분석결과 중금속 함량별 변화에도 $C_3$S와 $C_2$S 수화열에는 차이가 없었다.

• Korean Journal of Materials Research
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• v.22 no.12
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• pp.675-681
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• 2012

We aimed to examine the co-doping effects of 1/6 mol% $Mn_3O_4$ and 1/4 mol% $Cr_2O_3$ (Mn:Cr = 1:1) on the reaction, microstructure, and electrical properties, such as the bulk defects and grain boundary properties, of ZnO-$Bi_2O_3-Sb_2O_3$ (ZBS; Sb/Bi = 0.5, 1.0, and 2.0) varistors. The sintering and electrical properties of Mn,Cr-doped ZBS, ZBS(MnCr) varistors were controlled using the Sb/Bi ratio. Pyrochlore ($Zn_2Bi_3Sb_3O_{14}$), ${\alpha}$-spinel ($Zn_7Sb_2O_{12}$), and ${\delta}-Bi_2O_3$ (also ${\beta}-Bi_2O_3$ at Sb/Bi ${\leq}$ 1.0) were detected for all of the systems. Mn and Cr are involved in the development of each phase. Pyrochlore was decomposed and promoted densification at lower temperature on heating in Sb/Bi = 1.0 system by Mn rather than Cr doping. A more homogeneous microstructure was obtained in all systems affected by ${\alpha}$-spinel. In ZBS(MnCr), the varistor characteristics were improved dramatically (non-linear coefficient, ${\alpha}$ = 40~78), and seemed to form ${V_o}^{\cdot}$(0.33 eV) as a dominant defect. From impedance and modulus spectroscopy, the grain boundaries can be seen to have divided into two types, i.e. one is tentatively assigned to ZnO/$Bi_2O_3$ (Mn,Cr)/ZnO (0.64~1.1 eV) and the other is assigned to the ZnO/ZnO (1.0~1.3 eV) homojunction.

• 한국해양학회지
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• v.18 no.1
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• pp.49-54
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• 1983

sediments were collected from 23 ststions in Jinhae Bay and Cd, Cr, Cu, Fe, Ni, Mn, Pb and Zn were determined by atomic absorption spectrohotometry. The concentrations of Cd, Cr, Cu, Pb and Zn in the sediments decreased gradusally with increasing distance from the gead of Masan Bay, indicating pollutant transport from industrial and municipal wastewaters. But the levels of Co, Fe, Ni and Mn showed no difference througout the bay. analysis of correlation coefficients showed that Cd, Cr, Cu, Pb and Zn in the sediments were [losely associated to one another, whereas co, Fe and Ni were so associated.

• Advances in environmental research
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• v.3 no.4
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• pp.321-335
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• 2014

Eight trace metals, Cd, Co, Cr, Cu, Mn, Ni, Pb and Zn, were measured in the urban soil of Guwahati City, Assam, India from 31 sites representing five different types of land use, residential, commercial, industrial, public utilities, and roadside. Cd and Co occurred in very low concentrations (Cd << Co) in all types of land use without any significant variation from one type of land use to another. Ni concentrations were more than those of Co, and the concentrations depended on land use pattern. Average Cr and Cu concentrations were ${\geq}100mg/kg$, but Cr had a significantly higher presence in industrial land use. Pb concentrations showed similar trends. The two metals, Mn and Zn, were present in much larger amounts compared to the others with values ${\geq}300mg/kg$. Industrial and roadside soil contained much more Mn while commercial soil was enriched with Zn. Toxicity Characteristic Leaching Procedure (TCLP) was used for elucidating the mobility characteristics of the eight heavy metals. Mn suffered the highest leaching from commercial land (9.9 mg/kg on average) and also from other types of land. Co, Cu and Pb showed higher leachability from commercial soils but the leached concentrations were less than those of Mn. The two metals, Zn and Ni, were leached from residential land in considerable amounts. The TCLP showed Mn to be the most leachable metal and Cr the least.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.947-950
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• 2004

[ $ZnCr_2O_4$ ]에 $Li_2CO_3$를 $5{\sim}30wt%$ 범위에서 정량적으로 첨가한 감습재료에서 screen printing법으로 알루미나 기판 위에 후막으로 인쇄하고 $650\sim750^{\circ}C$에서 소결하여 후막 습도센서를 제작하였으며, $30\sim90%RH$ 범위에서 상대습도에 따른 저항 및 정전용량 특성을 조사하였다. $ZnCr_2O_4$에 $Li_2CO_3$가 5wt%가 첨가된 조성의 센서는 70%RH이상에서, 25wt%이상 첨가된 조성의 센서는 40%RH이하에서 저항 및 정전용량이 급격히 변화하는 switching 현상을 나타내었다. 반면, $ZnCr_2O_4$에 $Li_2CO_3$가 15wt%가 첨가된 조성의 센서는 선형적으로 저항은 감소하였고, 정전용량은 증가하였다.

• Journal of the Korean Chemical Society
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• v.43 no.2
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• pp.206-212
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• 1999

The main objective of the present investigation is to improve the photoluminescent performance of existing $Zn_2SiO_4:Mn$ phosphors by introducing a new co-dopant. The co-doping effect of Mg and/or Cr upon emission intensity and decay time was studied in the present investigation. The co-dopants incorporated into the $Zn_2SiO_4:Mn$ phosphors are believed to alter the internal energy state so that the change in emission intensity and decay time can be expected. Both Mg and Cr ions have a favourable influence on photoluminescence prpperties, for example, the Mg ion enhances the intensity of manganese green emission and the Cr ion shortens the decay time. The enhancement in emission intensity of $Zn_2SiO_4:Mn,\;Mg$ phosphors was interpreted by taking into account the result from the DV-X${\alpha}$ embedded cluster calculation. On the other hand, the energy transfer between Mn and Cr ions was found to be responsible for the shortening of decay time in$Zn_2SiO_4:Mn,\;Cr$ phosphors.

• Journal of Soil and Groundwater Environment
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• v.6 no.4
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• pp.25-40
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• 2001

In order to investigate the degree of heavy metal pollution, 280 urban gully-pot sediments were collected from 13 localities in eastern part of Seoul. The uncontaminated stream sediments were also studied for comparison. A series of studies have carried out concerning the physicochemical characteristics of the sediments and the distribution of Cd, Co, Cr, Cu, Ni, Pb, and Zn. Total metal concentrations of gully-pot sediments and uncontaminated stream sediments were analyzed using acid extraction. After predigestion with $NHO_3$, the sample was digested with mixed acid ($NHO_3$-$HClO_4$). The gully-pot sediments were characterized by very high concentrations of Zn, Cu, Pb and Cr, indicating an anthropogenic contribution of these metals to the sediment chemistry Heavy metal concentrations in the gully-pot sediments were 1-329 times higher than the mean content of metals in the uncontaminated stream sediments, depending on the metals. In particular, the highest mean concentrations of Zn, Cu, Pb and Cr were noticed in the gully-pot sediments from Yeouido, Junggu, Junggu, and Dongdaemungu, respectively. The mean value of total Zn concentration in the business and commercial areas is 2-3.5 times higher than that in industrial areas. This suggests that Zn is mainly derived from automobiles (rubber of automobile tires). The mean concentrations of Cu and Cr are significantly high in the commercial and industrial areas, indicating that industrial activities may cause the accumulation of Cu and Cr in the sediments. The Pb level in gully-pot sediments is comparatively low, due to the use of unleaded gasoline in automobiles since 1987.