• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.24 no.12
• /
• pp.962-968
• /
• 2011

In this study, we investigated the effects of Mn dopant (0.1~3.0 at% $Mn_3O_4$ sintered at 1000$^{\circ}C$ for 1 h in air) on the bulk trap (i.e. defect) and grain boundary properties of ZnO, ZM(0.1~3.0) using admittance spectroscopy (AS), and impedance-modulus spectroscopy (IS & MS). As a result, three kinds of defect were found below the conduction band edge of ZnO as 0.09~0.14 eV (attractive coulombic center), 0.22~25 eV ($Zn^{{\cdot}{\cdot}}_i$), and 0.32~0.33 eV ($V^{\cdot}_o$). The oxygen vacancy increased with Mn doping. In ZM, an electrically single grain boundary as double Schottky barrier was formed with 0.82~1.0 eV of activation energies by IS & MS. We also find out that the barriers of grain boundary of Mn-doped ZnO (${\alpha}$-factor=0.13) were more stabilized and homogenized with temperature compared to pure ZnO.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.6 no.3
• /
• pp.327-340
• /
• 1996

In this study, a series of $LiNbO_{3}$ crystals with different [Li]/[Nb] ratios, congruent $LiNbO_{3}$ crystals with doped Mg and with Mg and codoped with Mn were grown by the Czocharalski method. These were investigated by UV and IR spectrophotometry. Stoichiometry dependences of the UV absorption edge and the $OH^{-}$ absorption spectra were studied with different [Li]/[Nb] ratios. The position of the UV absorption edge adn the shape and peak point of the $OH^{-}$ absorption spectra changed monotonously upto a critical concentration of Mg ions. The mechanism of the incorporation of Mg ions changes at this concentration. The decomposition of the $OH^{-}$ absorption spectra using a Gaussian lineshape function showed that in Li-deficient crystals the absorption spectra consist of five components in contrast to more or less perfect stoichiometric crystals which reveal to three components. On the basis of these results, the intrinsic and the extrinsic defect structure models in $LiNbO_{3}$ crystals were examined. The behaviour of $\nu$ (OH) reflects the defect structure and supports the Li-site vacancy model as the intrinsic defect structure model and the corresponding extrinsic defect model. A brief discussion is also given of the behaviour of $\nu$ (OH) in $LiNbO_{3}$ crystals simultaneously doped with several kinds of impurity.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.24 no.11
• /
• pp.882-889
• /
• 2011

In this study, we have investigated the effects of Co doping on I-V curves, bulk trap levels and grain boundary characteristics of ZnO-$Bi_2O_3$ (ZB) varistor. From I-V characteristics the nonlinear coefficient (a) and the grain boundary resistivity (${\rho}_{gb}$) decreased as 32${\rightarrow}$22 and 18.4${\rightarrow}0.6{\times}10^9{\Omega}cm$ with sintering temperature (900~1,300$^{\circ}C$), respectively. Admittance spectra and dielectric functions show two bulk traps of zinc interstitial, $Zn_i^{{\cdot}{\cdot}}$(0.16~0.18 eV) and oxygen vacancy, $V_o^{{\cdot}}$ (0.28~0.33 eV). The barrier of grain boundaries in ZBCo (ZnO-$Bi_2O_3-Co_3O_4$) could be electrochemically single type. However, its thermal stability was slightly disturbed by ambient oxygen because the apparent activation energy of grain boundaries was changed from 0.93 eV at the 460~580 K to 1.13 eV at the 620~700 K. It is revealed that Co dopant in ZB reduced the heterogeneity of the barrier in grain boundaries and stabilized the barrier against the ambient temperature.

• Bulletin of the Korean Chemical Society
• /
• v.13 no.3
• /
• pp.248-252
• /
• 1992

$ZrO_2-dopedYb_2O_3solid$ solutions containing 1, 3, 5, 7 and 9 mol% $ZrO_2were$ synthesized from spectroscopically pure $Yb_2O_3$ and $ZrO_2$ powders and found to be rare earth C-type structure by XRD technique. Electrical conductivities were measured as a function of temperatures from 700 to $1050^{\circ}C$ and oxygen partial pressures from 1${\times}$$10^-5$ to 2${\times}$ $10^-1$atm. The electrical conductivities depend simply on temperature and the activation energies are determined to be 1.56-1.68 $_eV$. The oxygen partial pressure dependence of the electrical conductivity shows that the conductivity increases with increasing oxygen partial pressure, indicating p-type semiconductor. The $PO_2$ dependence of the system is nearly power of 1/4. It is suggested from the linearity of the temperature dependence of electrical conductivity and only one value of 1/n that the solid solutions of the system have single conduction mechanism. From these results, it is concluded that the main defects of the system are negatively doubly charged oxygen interstitial in low. $ZrO_2doping$ level and negatively triply charged cation vacancy in high doping level and the electrical conduction is due to the electronic hole formed by the defect structure.

• Journal of the Korean Chemical Society
• /
• v.25 no.4
• /
• pp.236-245
• /
• 1981

The electrical conductivities of oxidized pure and Ni-doped $SrTiO_3$ single crystals were measured as a function of the oxygen partial pressure($Po_2$) at temperature from 700 to $1200^{\circ}C$ and $Po_2$ of $10^{-8}$ to $10^{-1}$ atm. Plots of log ${\sigma}$ vs. 1/T at constant $Po_2$ were found to be linear, and the activation energies obtained from the slopes of these plots have an average value of 1.34 eV for oxidized pure and 1.06 eV for oxidized Ni-doped $SrTiO_3$ single crystals at $Po_2$'s between $10^{-8}$ to $10^{-1}$ atm. The log ${\sigma}$ vs. log $Po_2$ curves at constant temperature were found to be linear with an average slope of ${\frac{-1}{5.6}}\;{\sim}\;{\frac{-1}{6.2}}$ in the $Po_2$ ranges. From the agreement between experimental and theoretically predicted values for the electrical conductivity dependences on $Po_2$, an oxygen vacancy defect model was found applicable to oxidized pure and Ni-doped $SrTiO_3$ single crystals over the temperature range, 700~$1200^{\circ}C$. Conduction mechanisms were proposed to explain the dependences of electrical conductivity on temperature and $Po_2$.