• 한국재료학회지
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• 제21권7호
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• pp.377-383
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• 2011

Thermoelectric power, dc conductivity, and the dielectric relaxation properties of $La_2NiO_{4.03}$ are reported in the temperature range of 77 K - 300 K and in a frequency range of 20 Hz - 1 MHz. Thermoelectric power was positive below 300K. The measured thermoelectric power of $La_2NiO_{4.03}$ decreased linearly with temperature. The dc conductivity showed a temperature variation consistent with the variable range hopping mechanism at low temperatures and the adiabatic polaron hopping mechanism at high temperatures. The low temperature dc conductivity mechanism in $La_2NiO_{4.03}$ was analyzed using Mott's approach. The temperature dependence of thermoelectric power and dc conductivity suggests that the charge carriers responsible for conduction are strongly localized. The relaxation mechanism has been discussed in the frame of the electric modulus and loss spectra. The scaling behavior of the modulus and loss tangent suggests that the relaxation describes the same mechanism at various temperatures. The logarithmic angular frequency dependence of the loss peak is found to obey the Arrhenius law with activation energy of ~ 0.106eV. At low temperature, variable range hopping and large dielectric relaxation behavior for $La_2NiO_{4.03}$ are consistent with the polaronic nature of the charge carriers.

• 한국재료학회지
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• 제19권4호
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• pp.186-191
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• 2009

Thermoelectric power and resistivity are measured for the perovskite $LaNi_{1-x}Ti_xO_3$ ($x{\leq}0.5$) in the temperature range 77 K - 300 K. The measured thermoelectric power of $LaNi_{1-x}Ti_xO_3$ ($x{\leq}0.5$) increases linearly with temperature and is represented by A + BT. The x = 0.1 sample showed metallic behavior, the x = 0.3 showed metal and insulating transition around 150 K, and x = 0.5 showed insulating behavior the over the whole temperature range. The electrical resistivity of x = 0.1 shows linear temperature dependence over the whole temperature range and $T^2$ dependence. On the other hand, the electrical resistivity of x = 0.3 shows a linear relation between $ln{\rho}$ and $T^{-1/4}$ (variable range hopping mechanism) in the range of 77 K to 150 K. For x = 0.5, the temperature dependence of resistivity is characteristic of insulating materials; the resistivity data was fitted to an exponential law, such as ln(${\rho}/T$) and $T^{-1}$, which is usually attributed to a small polaron hopping mechanism. These experimental results are interpreted in terms of the spin polaron (x = 0.1) and variable range hopping (x = 0.3) or small polaron hopping (x = 0.5) of an almost localized $Ni^{3+}$ 3d polaron.

• 한국세라믹학회지
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• 제41권11호
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• pp.858-863
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• 2004

본 연구는 입방정 L $a_{2}$ 3/Ti $O_{2.84}$ 세라믹스의 전기전도율, 열기전력 그리고 자기적 특성에 대하여 조사하였다. 350 K 이하의 은도영역에서의 입방정 L $a_{2}$ 3/Ti $O_{2.84}$ 세라믹스의 열기전력은 음으로 나타났다 열기전력은 온도의 증가와 더불어 선형적으로 증가하여 A+BT의 형태로 표현가능 하였으며, Emin과 Wood가 제안한 모델과 잘 일치하였다. 이와 같은 열기전력의 온도의존성은 L $a_{2}$ 3/Ti $O_{2.84}$ 세라믹스의 전도 carrier가 small polaron임을 의미한다. L $a_{2}$ 3/Ti $O_{2.84}$ 세라믹스는 실온 이하의 특정온도에서 variable range hopping에서 small polaron hopping으로 변화하였다. 저온영역에서는 직류전도 기구해석은 Mott의 접근방식을 이용하였다. Mott의 보조변수 해석결과 Fermi면에서의 상태밀도 [N( $E_{F}$)]는 3.18${\times}$$10^{20}$ $cm^{-3}$e $V^{-1}$이었으며, 무질서에너지 $W_{d}$는 0.93로 고온에서의 활성화 에너지 보다 매우 크다. 200K와 300K온도 범위에서 log($\sigma$T)와 1/T의 직선 관계가 존재 하였으며, small polaron의 hopping energy는 0.15 eV였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1989년도 추계학술대회 논문집 학회본부
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• pp.65-67
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• 1989

To study hopping conducting mechanism in PAN(polyacrylonitrile) carbon fiber, the temperature and frequency dependence of electrical conductivity and magnetoresistance characteristics were investigated. Electrical conductivity in the range of $60^{\circ}K-300^{\circ}K$ show VRH(variable range hopping) properties which introduced by Mott's theory, and also such properties can be explained by the frequency dependence of electrical conductivity below $5{\times}10^6$ Hz. The negative magnetoresistance observed below 35KG magnetic field, and the properties difference between M40 and T300 with increasing magnetic field is supposed due to on effect connected with crystalline state and orientation of structure.

• 한국세라믹학회지
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• 제43권2호
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• pp.131-135
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• 2006

In this study, the dielectric, magnetic and transport properties of $Gd_{0.33}Sr_{0.67}FeO_3$ have been analyzed. The dielectric loss anomaly was found to be around 170 K. The activation energy corresponding to relaxation process of this dielectric anomaly was 0.17 eV. From the temperature dependence of the characteristic frequency, we concluded that the elementary process of the dielectric relaxation peak observed is correlated with polaron hopping between $Fe^{3+}\;and\;Fe^{4+}$ ions. The electrical resistivity displayed thermally activated temperature dependence above 200 K with an activation energy of 0.16 eV. In addition, the temperature dependence of thermoelectric power and resistivity suggests that the charge carrier responsible for conduction is strongly localized.

• Bulletin of the Korean Chemical Society
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• 제34권6호
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• pp.1679-1683
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• 2013

Intergrowth perovskite type complex oxides $La_{0.8}Ln_{0.2}Sr_2MnCrO_{7-{\delta}}$ (Ln=La, Nd, Gd, and Dy) have been synthesized by sol-gel method. Rietveld profile analysis shows that the phases crystallize with tetragonal unit cell in the space group I4/mmm. The unit cell parameters a and c decrease with decreasing effective ionic radius of the lanthanide ion. The magnetic studies suggest that the ferromagnetic interactions are dominant due to $Mn^{3+}$-O-$Mn^{4+}$ and $Mn^{3+}$-O-$Cr^{3+}$ double exchange interactions. Both Weiss constant (${\theta}$) and Curie temperature ($T_C$) increase with decreasing ionic radius of lanthanide ion. It was found that the transport mechanism is dominated by Mott's variable range hopping (VRH) model with an increase of Mott localization energy.

• 폴리머
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• 제27권4호
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• pp.323-329
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• 2003

기능성 도핑제인 di(2-ethylhexyl) sulffsuccinate sodium salt (NaDEHS)을 사용하여 화학적, 전기화학적 방법에 의한 연신성 폴리피롤을 합성하였다. 화학적, 전기화학적 방법에 의해 제조된 폴리피를 필름은 구역 연신 방법을 사용하여 1.0∼2.5배 연신시킬 수 있었으며, 연신된 폴리피를 필름의 전기 전도도를 측정하였다. 연신율이 증가함에 따라 필름의 전기 전도도는 증가함을 볼 수 있었다. 이러한 현상은 연신율에 따른 결정성 증가로 설명할 수 있었다. 온도변화에 따른 전하 이동 경로는 1.0-2.0배 연신된 폴리피롤의 경우 3차원 variable range hopping모델, 2.5배 연신된 폴리피롤의 경우 1차원 VHR모델에 적합함을 볼 수 있었다.

• 한국재료학회지
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• 제7권1호
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• pp.81-88
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• 1997

유리 형성제로 $B_{2}O_{3}$를 사용하고 CuO를 첨가한 vanadate계 3성분계 유리의 전기적 특성을 조사하였다. 각 조성별 결정화온도에서 열처리 시간을 다르게 하여 생성되는 결정상을 조사 하였으며, 결정화 특성에 따른 직류 전기 전도도의 변화를 분헉하였다. 생성 결정물은 XRD 분석결과 $V_{2}O_{5},\;{\alpha}-CuV_{2}O_{6}$로 판명 되었으며, 열처리 시간에 따라 $V_{2}O_{5}\;와\;{\beta}-CuV_{2}O_6$의 결정화도는 별다른 변화가 없었으나 ${\alpha}-CuV_{2}O_{6}$의 결정화도는 크게 변화하였고 ${\alpha}-CuV_{2}O_{6}$의 결정화도 증가에 따라 전기 전도도가 증가 하였다. 전기 전도도는 상온(303K)에서 유리 조성을 변화시켜 $10^{-2}~-10^{-4}{\Omega}^{-1}cm^{-1}$ 범위로 조절될수 있었다. $V_{2}O_{5}$ 함량이 증가할수록, 염기도($CuO/B_{2}O_{3}$)가 감소할수록 전기 전도도가 증가 하였다. 이 유리의 charge carrier는 전자인 n-type 반도체임이 seebeck coefficient 측정결과 판명되었으며, 전자 전도에 대한 활성화 에너지는 0.098-0.124eV로 계산되어졌다. 측정 온도인 $30~200^{\circ}C$에서 small polaron hopping conduction이 발생함이 관찰되었고, variable range hopping은 보이지 않았다.

• 한국전기전자재료학회논문지
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• 제15권3호
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• pp.220-226
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• 2002

Amorphous $Sb_{2-x}Bi_xTe_3$ (x = 0.0, 0.5 and 1.0) thin films were prepared by vacuum evaporation. The resistivity of 7he films decreases from 1.4{\times}10^{-2}$ to $8.84{\times}10^{-5}\Omega cm$ and the type of conductivity changes from p to n with the increase of the x value of the films. D.C. conduction studies on these films ate performed at various electric fields in the temperature range of 303-403 K. At low electric fields, two types of conduction mechanisms, i.e. the variable range hopping and the phonon assisted hopping are found to be responsible for the conduction, depending upon the temperature. The activation energy decreases from 0.082 to 0.076 eV in the temperature range of 303-363 K and from 0.47-0.456 eV in the second range of 363-403 K, indicating the shift of the Fermi level towards the conduction band edge and hence the change of the conduction from P to n type with the increase of the Bi concentration. Poole-Frankel emission dominates at high fields. The shape of the potential well of the localized centre is deduced and the mean free path of the charge carriers is also calculated.

• Bulletin of the Korean Chemical Society
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• 제30권11호
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• pp.2701-2706
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• 2009

The polymer blends containing polypyrrole (PPy) and the sulphonic acids such as β-naphthalene sulfonic acid (NSA), camphor sulfonic acid (CSA), and dodecylbenzenesulfonic acid (DBSA) were synthesized by in situ deposition technique in an aqueous media using ammonium per sulfate (APS) as an initiator. The obtained films were characterized by scanning electron microscopy (SEM), and the thermal behavior of these polymer blends was analyzed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The temperature-dependent (DC) conductivity of the obtained films shows a semiconducting behavior with a negative temperature coefficient of resistivity (TCR). The conductivity data were also analyzed through Mott’s equation, which provides the variable range hopping model in three dimensions. The parameters such as density of states at the Fermi energy, hopping energy, and hopping distance were calculated for PPy, PPy-NSA, PPy-CSA, and PPy-DBSA films, and the data were compared.