• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.31 no.5
• /
• pp.313-319
• /
• 2018

This study introduces a new investigation report on the microstructural and electrical property changes of $ZnO-Zn_2BiVO_6-Mn_3O_4$ (ZZMn), where 0.33 mol% of $Mn_3O_4$ and 0.5 mol% of $Zn_2BiVO_6$ were added to ZnO (99.17 mol%) as liquid phase sintering aids. $Zn_2BiVO_6$ contributes to the decrease of sintering temperatures by up to $800^{\circ}C$, and segregates its particles at the grain boundary, while $Mn_3O_4$ enhances ${\alpha}$, the nonlinear coefficient, of varistor properties up to ${\alpha}=62$. In comparison, when the sintering temperature is increased from $800^{\circ}C$ to $1,000^{\circ}C$, the resistivity of ZnO grains decreases from $0.34{\Omega}cm$ to $0.16{\Omega}cm$, and the varistor property degrades. Oxygen vacancy ($V_o^{\bullet}$) (P1, 0.33~0.36 eV) is formed as a dominant defect. Two different kinds of grain boundary activation energies of P2 (0.51~0.70 eV) and P3 (0.70~0.93 eV) are formed according to different sintering temperatures, which are tentatively attributed to be $ZnO/Zn_2BiVO_6$-rich interface and ZnO/ZnO interface, respectively. Accordingly, this study introduces a progressive method of manufacturing ZnO chip varistors by way of sintering ZZMn-based varistor under $900^{\circ}C$. However, to procure a higher reliability, an in-depth study on the multi-component varistors with double-layer grain boundaries should be executed.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2016.02a
• /
• pp.253-253
• /
• 2016

최근 세계적으로 대체 에너지는 중요한 이슈가 되고 있으며 그 중 열전 재료는 유망한 에너지 기술로서 주목 받고 있다. 특히 고 직접화 전자 소자의 발열 문제를 해결하기 위해, 소형화와 정밀 온도 제어가 가능한 박막형 열전 소자에 연구가 주목 받고 있다. 박막형 열전소자 중 산화물 반도체계에 대한 연구가 활발히 진행되고 있으며, 이러한 산화물 반도체계 중 In2O3는 BiTe, PbTe 등의 기존의 재료에 비해 독성이 낮을 뿐만 아니라 내 산화성 및 고온에서 열적 안정성이 우수하여 고온에서 적용 불가능한 금속계 열전 재료의 한계를 극복 할 수 있다는 장점을 가진다. 우수한 성능 가장 낮은 캐리어 밀도를 가지기 때문에 의 열전 재료는 높은 전기 전도도 및 제백 계수 그리고 낮은 열전도도 특성을 가져야만 한다. IZO:Sn(Zn 10 wt.%, Sn 800 ppm) 박막의 경우, 높은 전기 전도성을 가지면서 비정질 구조를 가진다. 이와 같이 비정질 구조를 가지는 박막 열전 재료는 격자에 의한 열 전도도가 낮기 때문에 결정질 구조에 비해 전체 열 전도도 값이 낮을 것으로 기대된다. 따라서 높은 전기 전도도를 가지면서 동시에 낮은 열 전도도를 가지게 되어 우수한 열전 특성을 가질 것이라 예상된다. 이러한 특성을 바탕으로 본 연구에서는 비정질 구조를 갖는 Zn와 미량의 Sn을 동시에 첨가한 In2O3박막의 전기적 특성및 열전 특성을 관찰하고자 한다. 본 연구에서는 magnetron sputtering법으로 IZO:Sn(Zn 10 wt.%, Sn 800 ppm) 타깃을 이용하여 기판 가열없이 DC Power 70 W, 작업 압력 0.7 Pa으로 SiO2 기판 위에 $400{\pm}20nm$ 두께의 박막을 증착하였다. 이러한 공정으로 만들어진 박막은 대기 중 후 열처리를 각각의 200, 300, 400, 500, $600^{\circ}C$ 온도에서 진행하였다. 박막의 미세 구조는 XRD를 통해 관찰하였다. 그리고 박막의 전기적 특성은 Hall effect measurement을 통해 측정하였고, 열전 특성은 Seebeck 상수의 측정을 통하여 평가하였다. XRD 확인 결과 RT에서 증착한 박막과 후 열처리 200, 300, 400, $500^{\circ}C$ 결과 비정질 구조를 보였고, 후열처리 $600^{\circ}C$에서는 결정의 회절 피크를 보였다. 전기적 특성의 경우, 후 열처리 온도가 증가함에 따라 전기 전도도는 감소한다. 이는 공기중의 산소가 박막에 침투하여 oxygen vacancy를 막아 캐리어 밀도가 감소한것에 기인 된 것으로 판단된다. 열전 특성의 경우 제백상수는 후 열처리 $600^{\circ}C$에서 가장 높은 제백상수를 나타낸다. 제백 상수는 수식에 따라 캐리어 밀도의 -2/3승에 비례하게 된다. 수식에 따라 후 열처리 $600^{\circ}C$에서 가장 낮은 캐리어 밀도를 가지기 때문에 가장 높은 제백 상수를 가지게 된다. 열전 성능 척도인 Power factor는 제백 상수의 제곱과 전기전도도의 곱으로 나타내는데, 후 열처리 $200^{\circ}C$에서 가장 높은 Power factor를 보인다. 이는 캐리어 밀도 감소에 따라 전기 전도도는 감소하였지만 이로 인해 제백상수는 증가하였고, 또한 캐리어 밀도 감소에 따라 이온화 불순물 산란의 감소에 의해 이동도의 증가에 의한 것으로 판단된다. 박막의 경우 기판의 영향으로 인해 열 전도도 측정이 어려워 열전 성능 지수(ZT)를 계산을 할 수 없지만, 마그네트론 스퍼터링법으로 증착한 IZO:Sn 박막은 비정질 구조를 가지므로 격자진동에 의한 열 전도도가 낮아 전체 열 전도도가 결정질에 비해 낮을 것이며 이는 높은 열전 성능 지수를 가질 것으로 예상된다.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.43 no.2 s.344
• /
• pp.8-12
• /
• 2006

We have fabricated ZnO thin film on $Pt/TiO-2/SiO_2/Si$ substrate by the sol-gel method and have investigated the effect of annealing temperature on the structural morphology and optical properties of ZnO thin films. The ZnO thin film annealed at $600^{\circ}C$ exhibits the highest c-axis orientation and its FWHM of X-ray peak is $0.4360^{\circ}C$. In the results of surface morphology investigation of ZnO thin film by using Am it is observed that ZnO thin film annealed at $600^{\circ}C$ exhibits the largest UV (ultraviolet) exciton emission at around 378nm and the smallest visible emission at around 510nm among these of ZnO thin films annealed at various temperatures. It is deduced that the ZnO thim film annealed at $600^{\circ}C$ is formed most stoichiometrically since the visible emission at around 510nm comes from oxygen vacancy or impurities.

• Journal of the Korean Ceramic Society
• /
• v.39 no.11
• /
• pp.1055-1062
• /
• 2002

The phase stability and the Low Temperature Degradation(LTD) mechanism of Tetragonal Zirconia Polycrystals(TZP), sintered specimens of $Y_2O_3$-Stabilized Zirconia(2Y-TZP), doped with trivalent cations, were evaluated by investigating meachnical properties, Raman spectra, lattice parameter variation and the oxygen vacancy behavior under applied electric field. XRD observation was put forward on 2Y-TZP doped with trivalent cation whose ionic radii were larger than $Zr^{4+}(Sc^{3+},\;Yb^{3+},\;Y^{3+},\;Sm^{3+},\;Nd^{3+},\;La^{3+})$ up to 2 mol% and sintered at 1500 h for 1h. For $La^{3+}$ doping, the stability of tetragonal phase was degraded due to the formation of the pyrochlore phase $(La_2Zr_2O_7)$ as the dopant content increased above exceeded 0.5 mol%. As the dosage increased, tetragonal phase maintained for the case of $Sc^{3+}$, whose radius was similar to $Zr^{4+}$, on the other hand, the cubic phase was formed for the cases of $Yb^{3+},\;Y^{3+},\;Sm^{3+},\;Nd^{3+}$. As the radii of dopant cation increased, c/a ratio increased and it was experimentally observed that the amount of monoclinic phase decreased when the specimens were annealed at $220{\circ}C$ for 500 h.

• Journal of the Korean Electrochemical Society
• /
• v.11 no.2
• /
• pp.89-94
• /
• 2008

We synthesized and investigated $(La_{0.75}Sr_{0.25})_{1-x}FeO_{3-\delta}$ perovskite oxides having different stoichiomety (x = 0, 0.02, 0.04, 0.06, 0.08) as cathode materials. SEM images and XRD patterns reveal that the synthesized powder has uniform size distribution and high degree of crystallinity. The electrochemical performances of the synthesized powders were investigated by AC impedance spectroscopy. Both the electric conductivity and the electrochemical performance showed the highest properties at the stoichiometry x = 0.02. Finally, we concluded that the variation of A-site deficiency results in the variation of the amount of oxygen vacancy and micro structure, which leads to the variation of electric conductivity and polarization resistance.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.1 no.2
• /
• pp.15-22
• /
• 1991

When $YBa_2Cu_3Ox$ is liquid-phase sintered at $925^{\circ}C$ in $O_2$ for 16h, liquid pockets are entrapped within the grains. The liquid pockets show a thin parallelepiped shape with short edge lengths in the c axis, even after reannealing $925^{\circ}C$ in $O_2$ for 16h. All grains in contact with the liquid matrix show the same shape. However, when liquid-phase sintered at 925^{circ}C in $N_2$ for 16h, the grains dispersed in the liquid matrix show a thicker parallelepiped shape than in $O_2$, and their shape remains intact even after reannealing at $925^{\circ}C$ in $N_2$ for 16h. The effect of atmosphere on the grain shape is expected to be due to the variation of oxygen vacancy concentraion in $CuO_2$ plane of tetragonal unit cell.

• Journal of the Korean Chemical Society
• /
• v.27 no.3
• /
• pp.183-188
• /
• 1983

The catalytic oxidation of $SO_2$ has been investigated in the presence of vacuum-activated 10 mol % Ni-doped ${\alpha}-Fe_2O_3$ under various partial pressures of $SO_2\;and\;O_2$ at temperatures from 320 to $440{\circ}C$. Over the temperature range $320{\sim}440{\circ}C$, the activation energy is 13.8 $kcal{\cdot}mol^{-1}$. The oxidation rates have been correlated with 1.5 order kinetics; first order with respect to $SO_2$ and 0.5 order with respect to $O_2$. From the kinetic data and conductivity measurements, the adsorption, oxidation mechanism of $SO_2$ and the defect structure of vacuum-activated 10 mol % Ni-doped {\alpha}-Fe_2O_3$ are suggested. $O_2\;and\;SO_2$ appear to be adsorbed essentially as ionic species. Two surface sites, probably an $O^{2-}$ lattice and an oxygen vacancy which is induced by Ni-doping, might be required to adsorb $SO_2\;and\;O_2$. The conductivity measurements and kinetic data indicate that the adsorption process of $SO_2\;{(SO_2+O^{2-}}_{(latt)}{\rightleftharpoons}{{SO_3}^-}_{(ads)}+e')$ is the rate-determining step.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.02a
• /
• pp.265-265
• /
• 2012

The adsorption of molecular $NH_3$ on rutile $TiO_2(110)-1{\times}1$ surfaces was investigated using a temperature-programmed desorption (TPD) technique combined with a molecular beam apparatus. A quantitative investigation into the TPD spectra of $NH_3$ was made for $NH_3$ adsorbed on two kinds of rutile $TiO_2(110)-1{\times}1$ surfaces with the oxygen vacancy ($V_O$) concentration of ~0% (p-$TiO_2(110)$) and ~5% (r-$TiO_2(110)$), respectively. On both surfaces, non-dissociative adsorption of $NH_3$ was inferred from a quantitative analysis on the amount of adsorbed $NH_3$ and those desorbed. With increasing coverage, the monolayer desorption feature shifted from 400 K toward lower temperatures until it saturates at 160 K, suggesting a repulsive nature in the interaction between $NH_3$ molecules. At the very low coverage regime, the desorption features were found to extend up to 430 K and 400 K on p-$TiO_2(110)$ and p-TiO(110), respectively. As a result, the saturation coverage of monolayer of $NH_3$ was higher on the p-$TiO_2(110)$ surface than on the p-TiO(110) by about 10%. The desorption energy ($E_d$) of $NH_3$ obtained by inversion of the Polanyi-Wigner equation indicated that the difference between the $E_d$'s of $NH_3$ (that is, $E_d(on\;p-TiO_2(110)$) - $E_d$(on p-TiO(110)) was 14 kJ/mol at ${\theta}(NH_3)=0$ and decreased to 0 as the coverage approached to a monolayer. The observed adsorption behavior of $NH_3$ was interpreted using an interaction model between $NH_3$ and surface defects on $TiO_2$ such as VO's and $Ti^{3+}$ interstitials.

• Applied Chemistry for Engineering
• /
• v.8 no.6
• /
• pp.954-959
• /
• 1997

The solid solutions of the $Sr_{1-X}M_XFeO_{3-y}$ (x=0.1, 0.2, 0.3, 0.4, 0.5, M=Ca) system having perovskite structures were prepared in air by heat treatment at 1473 K for 18hr. X-ray diffraction assigns cubic system for all the samples and shows that the lattice volume of each system decreases with increasing x value until x=0.3, but increases abruptly from x=0.4. The mole fractions of $Fe^{4+}$ ion($\tau$ value), the amounts of oxygen vacancy (y value) and finally nonstoichiometric chemical formulas for each composition were determined from Mohr salt analysis. TG/DTA thermal analysis (temperature range: 300~1173K) exhibits that 3-y values of the samples having x=0.1 and 0.2, decrease with temperature and increase almost reversibly with decreasing temperature. The samples of $x{\geq}0.3$, however, didn't show the reversible weight change and the 3-y values of them were nearly 2.5 in cooling process. Conductivities of each sample were varied within the semiconductivity range at relatively low temperature. And the conductivity at constant temperature decreases steadily with x value. The conduction mechanism of this ferrite system may be proposed as a hopping model of conducting electrons between the mixed valence states. At high temperature semiconductivity of each sample changed into metallic property.

• Journal of the Korean Chemical Society
• /
• v.30 no.1
• /
• pp.27-32
• /
• 1986

Electrical conductivities of NiO-$Y_2O_3$ systems containing 0.8, 1.6, and 3.2 mol% NiO have been measured in the temperature range of 400 to 1100$^{\circ}$C at $PO_2$'s of 1 ${\times}10^{-5}$ to 2 ${\times}10^{-1}$ atm. Plots of $log\sigma$ vs 1/T at constant $PO_2$'s are found to be linear with an inflection at temperature around 650$^{\circ}$C. The slopes are steeper in the high temperature region above 650$^{\circ}$C than in the low temperature region below 650$^{\circ}$C. The average activation energies are 41.8kcal/mol in the high temperature region and 12.5kcal/mol in the low temperature region. $PO_2$'s dependence value, 1/n, is 1/5.1~1/5.4 in the high temperature region and 1/5.9~1/6.2 in the low temperature region. The NiO-$Y_2O_3$ systems are found to be an electronic p-type semiconductor. The predominant defects in the systems are believed to be triply ionized yttrium vacancy in the high temperature region and doubly ionized oxygen interstitial in the low temperature region. Ionic contribution to the total conductivity is found from ${\sigma}^{\propto}PO_2$ in the temperatures below 650$^{\circ}$C.