• Journal of Electrical Engineering and Technology
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• 제1권1호
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• pp.120-126
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• 2006

Ferroelectric materials have been widely investigated for high density dynamic random access memories, opto-electrics, and tunable microwave devices due to their properties. In this study, we have investigated the dielectric properties of Ti doped $K(Ta,\;Nb)O_3$ thin films. By doping Ti Into the $K(Ta,Nb)O_3$ system, Ti with a valence value of +4 will substitute Ta or Nb ions with a valence value of +5. This substitution will introduce an acceptor state. Therefore, this introduced acceptor state will reduce dielectric loss by trapping electrons. Using 3% Ti-doped $K(Ta,Nb)O_3\;targets,\;K(Ta,Nb)O_3$:Ti films were grown in MgO(001) crystals using pulsed laser deposition. First, growth conditions were optimized. A reduction in the loss tangent was observed for Ti-doped $K(Ta,Nb)O_3$ relative to undoped films, although a reduction in tunability is also seen. The crystallinity, morphology, and tunability of $K(Ta,Nb)O_3$:Ti films are reported.

• 한국물환경학회지
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• 제29권2호
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• pp.176-183
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• 2013

The variation of the stable region of arsenic compounds in aqueous environment with temperature has been investigated by constructing the Pourbaix diagram of arsenic at different temperatures. The standard potential corresponding to the boundary between arsenic compounds with different charge valence was estimated to be decreased with temperature, which means the stability of arsenic compound with +5 charge valence increases. The distribution diagram of the most highly oxidized arsenic compound showed that arsenic acid is formed at higher pH and arsenate is generated at lower pH as temperature rises. The aquatic toxicity due to arsenic compounds was considered to be decreased with temperature in the neutral pH condition based on the $LD_T$ value defined in this study.

• 한국세라믹학회지
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• 제38권4호
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• pp.360-364
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• 2001

고상반응법(solid-state reaction)으로 산화물 초전도체 Bi$_{2+x}$ Sr$_{1.8}$ $CaCu_2$$O_{8+\delta}$(-0.2$\leq$x$\leq$0.2)을 제조하여 조성변화에 따른 산소량과 Bi 이온의 하전가(valence)가 구조변조의 주기에 미치는 영향을 조사하였다. 2212상의 단일상 고용한계는 -0.1$\leq$x$\leq$0.1 영역이었다. 이 영역에서 x의 증가에 따라 격자상수 c는 감소를 보이며, 온셋 임계온도 Tc$^{on}$ 과 산소량은 증가하는 경향을 보였다. 또한, Bi 이온의 하전기와 구조변조의 주기는 단일상 고용한계 영역 내에서 x의 증가에 따라 감소하는 경향을 보이고 있다. 구조변조의 주기는 산소량이 증가함에 따라 감소하고 Bi 이온의 하전가 증가에 따라 증가함을 보였다. 즉, 산소의 절대량과 Bi 이온의 하전가에 따라 구조변조의 주기가 변화하는 것을 알 수 있었다.

• 한국자기학회지
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• 제20권2호
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• pp.68-74
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• 2010

핵자기공명은 물질 내부의 국소적인 스핀 환경에 대한 정보를 제공하기 때문에 자성체 연구에 대단히 유용하다. 자성체 내 이온의 원자가 혹은 자기모멘트, 스핀들의 기울어짐각, 오비탈 상태 등을 직접 측정할 수 있게 해주며 자성이온들의 위치나 자구와 자구벽의 변화 등에 대한 정보를 제공한다. 이렇게 정보를 제공할 수 있는 단순화된 원리를 적용사례를 들어 설명한다.

• Bulletin of the Korean Chemical Society
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• 제13권4호
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• pp.385-388
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• 1992

The transition probabilities for the thermal intramolecular electron transfer and the optical intervalence transfer band for a symmetric mixed-valence Cu(I)-Cu(II) compound were used to extract the PKS parameters $\varepsilon$ = -1.15, ${\lambda}$ = 2.839, and ${\nu}g$- = 923 $cm^{-1}$. These parameters determine the potential energy surfaces and vibronic energy levels. Three pairs of vibrational levels are below the top of the energy barrier in the lower potential surface. The contribution of each vibrational state to the intramolecular electron transfer was calculated. It is shown that the three pairs of vibrational states below the top of the barrier are responsible for most of the electron transfer at 261-306 K. So the intramolecular electron transfer in this system is a tunneling process. The transition probability exhibits the usual high-temperature Arrhenius behavior, but at lower temperature falls off to a temperature-independent value as tunneling from the lowest levels becomes the limiting process.

• Asia Marketing Journal
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• 제26권1호
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• pp.23-30
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• 2024

Firms often engage in manipulating online reviews as a promotional activity to influence consumers' evaluation on their products. With the prevalence of the promotional activities, consumers may notice and discount the reviews generated by the promotional activities. Discounting the firm-generating reviews may cause systematic measurement errors in the valence variable and lead to a negative bias when estimating the effect of consumers' organic reviews on demand. To correct the bias, this study proposes including product-specific bias-correction terms representing the proportion of extreme reviews in analysis. For illustration, the proposed method is applied to a demand model for data of movies released in South Korea. The results confirm a negative bias in the estimate of the valence sensitivity of demand. The negative bias potentially leads to an underestimation of the magnitude of the contagion effect through social interactions, a key component of evaluating the value of a satisfied consumer.

• Bulletin of the Korean Chemical Society
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• 제24권6호
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• pp.712-716
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• 2003

The semi-diabatic potential energy surfaces (PESs) of the excited states of polyatomic molecules can be constructed for use in ab initio molecular dynamics (AIMD) studies by relying on the continuity of the electronic energy, oscillator strength, and spherical extent of an excited state along with first derivatives of these quantities as computed by using the equation-of-motion coupled-cluster (EOM-CC) method. The semidiabatic PESs of both the π → $π^*$ valence excited state and the 3s-type Rydberg state of ethylene are presented and discussed in this paper, in conjunction with some of the AIMD results we obtained for these states.

• 공업화학
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• 제28권1호
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• pp.64-72
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• 2017

본 연구에서는 다양한 증진제에 따른 $CH_4-SCR$ 반응특성을 확인하기 위하여 $Pt/Al_2O_3$를 기본으로 한 촉매에 알칼리, 알칼리 토류 금속을 담지하여 습식함침법으로 제조한다. 본 연구를 통해 $Pt/Al_2O_3$ 촉매에 Na를 담지시킬 경우 Pt와 Na 원자간 electronegative gap의 발생으로 Pt의 valence state 변화를 일으키며, 금속상 Pt의 비율이 증가됨을 확인할 수 있다. 또한 Na 첨가를 최적화시켜 제조한 촉매의 금속상 Pt종은 촉매표면에서 NO species 흡착 증진과 환원제로 사용되는 $CH_4$의 $CO_2$로의 산화를 억제시킨다. 이때, Na/Pt의 mole ratio는 4.0이 최적화이며, $CH_4-SCR$ 효율이 가장 우수하다.

• 대한화학회지
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• 제57권6호
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• pp.697-702
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• 2013

The addition reaction of cyclopropane with $MgH_2$ has been investigated using the B3LYP density functional method employing several split-valence basis sets. Both along the and perpendicular to the cyclopropane ring approach has been reported. It is shown that the reaction proceeds via a four-centered transition state. Calculations at higher levels of theory were also performed at the geometries optimized at the B3LYP level, but only slight changes in the barriers were observed. Structural parameters for the transition state are also reported.

• 한국재료학회지
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• 제18권3호
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• pp.143-147
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• 2008

Fe compounds in scoria as distributed in the south-western area of Jeju Island were investigated using X-ray fluorescence spectroscopy, X-ray diffractometry, and $^{57}Fe$ $M{\ddot{o}}ssbauer$ spectroscopy. The samples were prepared from four parasite volcanoes. It was found that these samples are typical basalt comprised of $SiO_2$, $Al_2O_3$, Fe, and silicate minerals. The $M{\ddot{o}}ssbauer$ spectra showed doublets for olivine, pyroxene, and ilmenite as well as sextets for hematite and magnetite. The valence state of Fe is chiefly a 3+ charge state with a slight 2+ charge state. It is expected that these results will add to the body of information related to the formation mechanisms of Jeju Island.