La_0.5Sr_0.5CrO₃ 세라믹스의 전기전도특성

정우환,Jung, Woo-Hwan 한국재료학회 2016 한국재료학회지 Vol.26 No.1

The electrical transport properties of $La_{0.5}Sr_{0.5}CrO_3$ below room temperatures were investigated by dielectric, dc resistivity, magnetic properties and thermoelectric power. Below $T_c$, $La_{0.5}Sr_{0.5}CrO_3$ contains a dielectric relaxation process in the tangent loss and electric modulus. The $La_{0.5}Sr_{0.5}CrO_3$ involves the transition from high temperature thermal activated conduction process to low temperature one. The transition temperature corresponds well to the Curie point. The relaxation mechanism has been discussed in the frame of electric modulus spectra. The scaling behavior of the modulus suggests that the relaxation mechanism describes the same mechanism at various temperatures. The low temperature conduction and relaxation takes place in the ferromagnetic phase. The ferromagnetic state in $La_{0.5}Sr_{0.5}CrO_3$ indicates that the electron - magnon interaction occurs, and drives the carriers towards localization in tandem with the electron - lattice interaction even at temperature above the Curie temperature.

La₂NiO₄₊_δ세라믹스의 유전이완 및 전기전도특성

정우환,Jung, Woo-Hwan 한국재료학회 2011 한국재료학회지 Vol.21 No.7

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.

저온에서 La_2/3+xTiO_3-_δ (x = 0, 0.13)세라믹스의 전자전도특성

정우환,Jung, Woo-Hwan 한국재료학회 2014 한국재료학회지 Vol.24 No.11

The thermoelectric power and dc conductivity of $La_{2/3+x}TiO_{3-{\delta}}$ (x = 0, 0.13) were investigated. The thermoelectric power was negative between 80K and 300K. The measured thermoelectric power of x = 0.13 increased linearly with increased temperatures and was represented by $S_0+BT$. The x = 0 sample exhibited insulating behavior, while the x = 0.13 sample showed metallic behavior. The electric resistivity of x = 0.13 had a linear temperature dependence at high temperatures and a T3/2 dependence below about 100K. On the other hand, the electric resistivity of x = 0 has a linear relation between $ln{\rho}/T$ and 1/T in the range of 200 to 300K, and the activation energy for small polaron hopping was 0.23 eV. The temperature dependence of thermoelectric power and the resistivity of x = 0 suggests that the charge carriers responsible for conduction are strongly localized. This temperature dependence indicates that the charge carrier (x = 0) is an adiabatic small polaron. These experimental results are interpreted in terms of spin (x = 0.13) and small polaron (x = 0) hopping of almost localized Ti 3d electrons.

Gd0.33Sr0.67FeO3 세라믹스의 전기전도특성

정우환 한국세라믹학회 2006 한국세라믹학회지 Vol.43 No.2

In this study, the dielectric, magnetic and transport properties of Gd0.33Sr0.67FeO3 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 0.17eV. 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 Fe3+ and Fe4+ ions. The electrical resistivity displayed thermally activated temperature dependence above 200 K with an activation energy of 0.16eV. In addition, the temperature dependence of thermoelectric power and resistivity suggests that the charge carrier responsible for conduction is strongly localized.

La0.7Sr0.3FeO3 세라믹스의 교류 전도특성

정우환 한국세라믹학회 2007 한국세라믹학회지 Vol.44 No.11

We have studied the ac conductivity of insulating La0.7Sr0.3FeO3 80-300 K. We have analyzed experimental results in the frame works of the quantum-mechanical tunneling mechanism (QMT) andthe hopping of barrier mechanism (HOB). We observed that small polaron QMT model is the most suitable mechanism for the lowtemperature ac conductivity of La0.7Sr0.3FeO3.

Gd_0.33Sr_0.67FeO₃ 세라믹스의 전기전도 특성

정우환,Jung, Woo-Hwan 한국세라믹학회 2006 한국세라믹학회지 Vol.43 No.2

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.

$Pb(Co_{1/3}Nb_{2/3})O_3-PbTiO_3-PbZrO_3$계 압전세라믹의 조성에 따른 압전 착화 소자의 특성 및 경시변화특성

정우환,박인철,김진호,조상희 한국전기전자재료학회 1992 電氣電子材料學會誌 Vol.5 No.1

본 연구는 Pb( $Co_{1}$3/Nb$_{2}$3/) $O_{3}$-PbTi $O_{3}$-PbZr $O_{3}$계 압전세라믹스의 조성에 따른 착화소자특성과 기계적응력 인가시의 압전열화현상에 대하여 조사하였다. 그 결과 상경계 조성에서 소결밀도, $K_{33}$ 및 출력전압이 최고치를 나타내었으며 능방정계조성에서는 조성의 변화에 따른 소결 및 전기적특성의 변화는 정방정계조성에 비하여 작았다. 기계적 응력 인가시의 압전퇴화현상은 분역의 재배열로 설명할 수 있었다.

LaNi_1-xTi_xO₃(x∼0.5) 세라믹스의 전기전도 특성

정우환,Jung, Woo-Hwan 한국재료학회 2009 한국재료학회지 Vol.19 No.4

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.

이중 층 La_1.4(Sr_0.2Ca_1.4)Mn₂O₇ 세라믹스의 저온에서의 Small Polaron Hopping 전도

정우환,Jung, Woo-Hwan 한국재료학회 2008 한국재료학회지 Vol.18 No.1

The dc resistivity and thermoelectric power of bilayered perovskite $La_{1.4}(Sr_{0.2}Ca_{1.4})Mn_2O_7$ were measured as a function of the temperature. In the ferromagnetic phase, ${\rho}(T)$ was accurately predicted by $a_0+a_2T^2+a_{4.5}T^{4.5}$ with and without an applied field. At high temperatures, a significant difference between the activation energy deduced from the electrical resistivity and thermoelectric power, a characteristic of small polarons, was observed. All of the experimental data can be feasibly explained on the basis of the small polaron.

고온에서의 La_0.75Ba_0.25MnO₃ 세라믹스의 전기전도 및 열전특성

정우환,Jung, Woo-Hwan 한국재료학회 2008 한국재료학회지 Vol.18 No.4

In this study, the thermoelectric power and resistivity of the perovskite manganite $La_{0.75}Ba_{0.25}MnO_3$ were investigated in the temperature range 300K-1200K. The electrical resistivity and thermoelectric power indicate a transport mechanism dominated by adiabatic small-polaron hopping. The power factor increases from $2{\times}10^{-6}W/mK^2$ to $1{\times}10^{-5}W/mK^2$ as to the temperature increases from 400K to 1200K, which indicates that the compound is highly feasible as a thermoelectric material at high temperatures.